Assessment MICRO Flashcards

Question

Bacteria are: A. Unicellular, prokaryotic organisms B. Multicellular, prokaryotic organisms C. Unicellular, eukaryotic organisms D. Multicellular, eukaryotic organisms

Answer 1

A. Unicellular, prokaryotic organisms ## Footnote Bacteria are single-cell prokaryotic microorganisms. Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals. Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.

Answer 2

D. Viruses ## Footnote Among clinically relevant organisms, bacteria are single-cell prokaryotic microorganisms. Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals. Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.

Answer 3

D. Flagella ## Footnote The flagellins of different bacterial species presumably differ from one another in primary structure. They are highly antigenic (H antigens), and some of the immune responses to infection are directed against these proteins.

Answer 4

C. N-glycolylmuramic acid and an increase in lipid content ## Footnote Mycobacterium spp. have an unusual cell wall structure. The cell wall contains N-glycolylmuramic acid instead of N-acetylmuramic acid, and it has a very high lipid content, which creates a hydrophobic permeability barrier.

Answer 5

C. Calcium dipicolinate ## Footnote The heat resistance of spores is partly attributable to their dehydrated state and in part to the presence in the core of large amounts (5–15% of the spore dry weight) of calcium dipicolinate, which is formed from an intermediate of the lysine biosynthetic pathway.

Answer 6

C. Peptidoglycan ## Footnote Microorganisms that lack cell walls (commonly called mycoplasmas and making up the class Mollicutes) and do not synthesize the precursors of peptidoglycan

Answer 7

D. H2S production ## Footnote Erysipelothrix rhusiopathiae is the only gram-positive bacillus that produces hydrogen sulfide when inoculated into triple sugar iron agar.

Answer 8

D. Stationary phase

Answer 9

C. Legionella ## Footnote Because of their faint staining, Legionella spp. are not usually detectable directly in clinical material by Gram stain. The use of 0.1% fuchsin substituted for safranin in the Gram-stain procedure may enhance the visibility of the organisms.

Answer 10

A. The slide was inadequately decolorized with acetone/alcohol ## Footnote Problems with analysis of Gram staining generally result from errors including interpretation of the slide (smear prepared too thick), excessive heat fixing, and improper decolorization. Inadequate decolorization with acetone alcohol results in a smear in which the host cells (neutrophils and squamous cells) as well as bacteria all appear blue

Answer 11

D. 300 oil immersion fields ## Footnote Bailey and Scott's: Before an AFB smear is reported as negative, it should be examined carefully by scanning at least 300 oil immersion fields (magnification ×1000), equivalent to three full horizontal sweeps of a smear that is 2 cm long and 1 cm wide. (DOH 2 cm x 3 cm)

Answer 12

D. Spores ## Footnote The Schaeffer–Fulton stain is a technique designed to isolate endospores by staining any present endospores green, and any other bacterial bodies red.

Answer 13

B. Flagella

Answer 14

D. Catalysts that have become inactivated after repeated use ## Footnote The 2 most common causes of failure of GasPak system are a defective gasket in the jar lid that allows escape of gas from inside the jar and inactivated catalyst pellets.

Answer 15

B. Sheep ## Footnote Sheep RBCs are used in blood agar plates because they are readily available and less inhibitory than cells of other species. The type of hemolysis is determined by the source of RBCs. Sheep RBCs are chosen because of the characteristically clear hemolysis produced by β-hemolytic streptococci, Staphylococcus, and other pathogens producing β-hemolysins. Sheep blood does not support the growth of Haemophilus haemolyticus, eliminating the possibility of confusing it with β-hemolytic streptococci in throat cultures.

Answer 16

C. The organism can sustain high salt concentrations and ferment mannitol

Answer 17

D. Trimethoprim lactate

Answer 18

B. Nystatin inhibits fungi and molds ## Footnote MTM: Modified Thayer-Martin Medium 1. Vancomycin inhibits the growth of gram-positive bacteria 2. Colistin inhibits the growth of gram-negative bacteria except N. gonorrhoeae 3. Nystatin inhibits the growth of fungi 4. Trimethoprim lactate prevents swarming of Proteus

Answer 19

B. Chocolate agar

Answer 20

B. Cefsulodin–Irgasan–Novobiocin (CIN) agar ## Footnote CIN agar inhibits the growth of many other organisms from the family Enterobacteriaceae. Yersinia spp. are also recovered from MacConkey and Salmonella-Shigella agars

Answer 21

B. Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth ## Footnote TCBS agar is used to grow Vibrio cholerae, which appear as yellow colonies as a result of the use of both citrate and sucrose. APW is used as an enrichment broth and should be subcultured to TCBS agar for further evaluation of Vibrio colonies

Answer 22

A. Inoculate cycloheximide-treated McCoy cells ## Footnote Chlamydiae are strict intracellular organisms and must be cultured using living cells

Answer 23

C. Salmonella typhimurium ## Footnote Salmonella is the only distractor that produces H2S. Also, Klebsiella and E. coli produce acid/acid reactions in TSI.

Answer 24

D. Buffered charcoal yeast extract agar

Answer 25

A. Uses 15 lbs of pressure for 15 minutes ## Footnote The traditional gravity displacement of steam sterilization cycle is 121˚C for 15 minutes at 15 pounds per square inch. Ethylene dioxide is an alternative sterilization method.

Answer 26

B. BSC Class II, A1

Answer 27

D. BSC Class II, B1

Answer 28

C. 1:10 ## Footnote Human blood contains substance that may inhibit microbial growth. Diluting blood in culture broth reduces the concentration of these substances as well as any antibiotics that may be present. The recommended blood-broth ratio is 1:5 to 1:10. Dilutions less than this may cause blood to clot, trapping microorganisms in the clot. Greater dilutions may increase the time of detection.

Answer 29

C. Inactivates neutrophils and components of serum complement ## Footnote Most commercially available blood culture media contain sodium polyanethol sulfonate (SPS) in concentration between 0.025 and 0.050%. SPS has anticoagulant activity and inactivates neutrophils as well as some antibiotics including gentamicin and polymyxin. It also precipitates components of serum complement.

Answer 30

D. Aspirate urine aseptically from the catheter tubing ## Footnote Indwelling catheters are closed systems, and should not be disconnected for specimen collection. Urine samples should not be collected from catheter bags, and Foley catheter tips are unsuitable for culture because they are contaminated with colonizing organisms. Urine from indwelling catheters should be collected by aseptically puncturing the tubing (collection port).

Answer 31

D. Urine for culture of acid-fast bacilli ## Footnote Urine is an appropriate specimen for the detection of renal tuberculosis. Since feces contain anaerobic organisms as part of the indigenous flora, it is an unacceptable specimen for anaerobic culture. Foley catheter tips are also not acceptable for culture because they are contaminated with colonizing organisms. Gram stain smears of rectal swabs for N. gonorrhoeae should also not be performed, since the presence of organisms with similar morphologies may lead to over interpretation of smears.

Answer 32

B. Cary-Blair

Answer 33

D. Sterile saline or 70% alcohol

Answer 34

C. Pleural fluid, brain abscess ## Footnote Materials collected from sites not harboring indigenous normal flora (sterile body fluids, abscesses, exudates and tissue) should be culture for anaerobic bacteria, however, since anaerobes normally inhabit the skin and mucus membrane as part of indigenous normal flora, specimens such as urine, sputum and vaginal, eye and ear swabs are not acceptable for culture.

Answer 35

C. A syringe filled with pus, obtained before administration of antibiotics ## Footnote The use of swabs for collection of specimens for anaerobic culture is discouraged. Aspiration with a needle and syringe is recommended. Whenever possible cultures should be obtained before the administration of antibiotics to optimize organism recovery

Answer 36

A. In less than 15 mins

Answer 37

C. Chocolate agar plate ## Footnote Enriched media such as chocolate agar has no inhibitory effects on bacterial growth and contains additional nutrients that support the growth of fastidious organisms such as H. influenzae and Neisseria.

Answer 38

C. -20C ## Footnote Urine, stool, viral specimens, sputa, swabs, and foreign devices such as catheters should be stored at 4°C. Serum for serologic studies may be frozen for up to 1 week at –20°C, and tissues or specimens for long-term storage should be frozen at –70°C.

Answer 39

C. Cation content of media ## Footnote Variations in the concentrations of divalent cations, primarily calcium and magnesium affect the results of aminoglycoside, tetracycline and colistin test with Pseudomonas aeruginosa isolates. A cation concentration that is too high results in smaller zone sized and a concentration that is too low increase zone sizes.

Answer 40

C. The depth of the media was too thin ## Footnote All Mueller Hinton Agar used for disk diffusion susceptibility testing should be poured to a depth of 4mm. If the depth of the media is <4mm, this may be associated with excessively large zones and false positive susceptibility results. Agar that is >4mm in depth may cause excessively small zone sizes.

Answer 41

B. Every week ## Footnote Daily disk diffusion quality control can be converted to weekly testing when 30 days of consecutive testing demonstrated no more than 3 antibiotic/ organism combinations outside the acceptable limits.

Answer 42

B. Decreased ## Footnote The amount of antibiotic used in disk diffusion susceptibility testing is standardized and constant. Once the disk is placed on the inoculated plate and makes contact with the agar, the antibiotic in the disk begins to diffuse out. As it diffuses into the media, the concentration of antibiotic gets lower the further it diffuses from the disk.

Answer 43

C. Zones of larger diameter would result ## Footnote A delay of more than 15 minutes between placing the disks on an inoculated plate and incubation permits excess prediffusion of the antimicrobial agent from the disk. This would result in a larger than expected zone diameter.

Answer 44

B. Too many organisms in the inoclum ## Footnote To ensure the reproducibility of disk diffusion testing, the inoculum must be standardized. If the inoculum is too dense (too many organisms) zone sizes would be smaller than expected and appear falsely resistant.

Answer 45

A. The swarming area should be ignored ## Footnote A thin film of growth appearing in the zone area of inhibition around the susceptibility disk should be ignored when swarming Proteus or other organisms are encountered. Discontinuous, poor growth or tiny colonies near the end of the zone should also be ignored.

Answer 46

B. Penicillin ## Footnote Penicillin inhibits penicillin-binding proteins that are essential to peptidoglycan (cell wall) synthesis. Chloramphenicol inhibits protein synthesis, colistin increases cell membrane permeability and sulfamethoxazole inhibits folate metabolism.

Answer 47

A. Catalase production and coagulase test ## Footnote The gram stain and culture growth describe a Staphylococcus species. Catalase production confi rms that the organism belong to the genus Staphylococcus and coagulase is used to differentiate S. aureus from coagulase negative staphylococci.

Answer 48

A. Produces only free coagulase and is most likely S. aureus ## Footnote Slide coagulase - cell-bound coagulase or clumping factor Tube coagulase - free coagulase

Answer 49

B. Novobiocin susceptibility ## Footnote The organism in this urine culture is a Staphylococcus species. Coagulase will differentiate S. aureus from coagulase negative staphylococci (CoNS) and novobiocin susceptibility will differentiate S. saprophyticus from other CoNS. S. saprophyticus is a common cause of urinary tract infections in young females

Answer 50

A. S. intermedius ## Footnote S. intermedius infects mammals and certain birds but not usually humans. Cases involving humans result from animal bites and are most often seen in persons who work closely with animals.

Answer 51

A. Acetoin ## Footnote The production of acetoin by S. aureus from glucose or pyruvate differentiates it from S. intermedius, which is also coagulase positive. This test is also called the VP test. Acetoin production is detected by addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation. A distinct pink color within 10 minutes denotes a positive test.

Answer 52

D. Staphylococcus aureus

Answer 53

B. S. epidermidis ## Footnote S. epidermidis produces an extracellular slime that enhances the adhesion of these organisms to indwelling plastic catheters. The slime production is considered a virulence factor and is associated with infections from prostheses.

Answer 54

B. The organism is most likely a contaminant ## Footnote Coagulase-negative staphylococci are commonly associated with contaminated blood cultures; however, they are also increasing as a cause of true bacteremia. Significant bacteremia in a patient with endocarditis is usually continuous and low grade. In most cases, all blood cultures drawn will yield positive results. The facts that only 1 bottle of 1 set was positive, and that the bottle did not become positive until day 5 of incubation indicate that this isolate is most likely a contaminant.

Answer 55

B. Fails to grow on mannitol salt agar

Answer 56

B. Streptococcus

Answer 57

D. Sodium chloride

Answer 58

B. Phenol red

Answer 59

B. D-zone test ## Footnote By using a 15-μg erythromycin disk adjacent to a 2-μg clindamycin disk in a disk diffusionprocedure, a flattening of the clindamycin zone occurs in inducible clindamycin resistance, causing the zone to look like the letter D. This is referred to as being D-zone positive. CLSI recommends that inducible clindamycin resistant strains be reported as resistant with a comment that clindamycin may still be effective in some patients.

Answer 60

B. Erythromycin resistant, clindamycin sensitive

Answer 61

A. Alpha hemolysis

Answer 62

B. Streptococcus pyogenes ## Footnote Streptococcus pyogenes Not considered normal flora Inhabits skin and upper respiratory tract of humans, carried on nasal, pharyngeal, and, sometimes, anal mucosa; presence in specimens is almost always considered clinically significant

Answer 63

B. Antigenic

Answer 64

A. Bile esculin, PYR, bacitracin, and hippurate ## Footnote Bile esculin, PYR, bacitracin and hippurate are biochemical test for the presumptive or definitive identifi cation of beta hemolytic streptococci. Such as S. pyogenes, S. aggalactiae and Enterococcus.

Answer 65

B. LIM broth (Todd-Hewitt broth with colistin and nalidixic acid) ## Footnote Detection of group B streptococcus (GBS) in the genital and gastrointestinal tracts of pregnant women can identify infants at risk for GBS infection. The CDC recommends the collection of vaginal and rectal swab or a single swab inserted first into the vagina and then the rectum at 35 to 37 weeks of gestation. The swab(s) should be inoculated into a selective broth medium such as LIM broth (Todd-Hewitt broth with colistin and nalidixic acid). The use of vaginal/rectal swabs and selective broth medium greatly increases the recovery of GBS.

Answer 66

B. Streptococcus agalactiae

Answer 67

D. Bile solubility ## Footnote Bile solubility testing of alpha hemolytic streptococci differentiates S. pneumoniae (soluble) from other alpha-hemolytic streptococci such as viridans streptococci (insoluble).

Answer 68

C. Streptococcus pneumoniae ## Footnote Optochin susceptibility is used to differentiate S. pneumoniae, which are susceptible from other alpha hemolytic streptococci which are resistant.

Answer 69

C. ≥ 14 mm

Answer 70

B. Glomerulonephritis, rheumatic fever ## Footnote Non-infectious sequelae associated with infection with Streptococcus pyogenes are glomerulonephritis and rheumatic fever.

Answer 71

D. PYR negative

Answer 72

D. Streptococcus pneumoniae

Answer 73

C. Streptococcus pyogenes

Answer 74

C. Streptolysin O ## Footnote Streptolysin O - subsurface hemolysis Streptolysin S - surface hemolysis

Answer 75

B. Streptococcus pneumoniae colonies on a blood agar plate ## Footnote The bile solubility test can be performed directly by dropping 2% sodium deoxycholate onto a few well-isolated colonies of S. pneumoniae. The bile salts speed up the autolysis observed in pneumococcal cultures. The colonies lyse and disappear when incubated at 35°C for 30 min, leaving a partially hemolyzed area on the plate.

Answer 76

B. Group B streptococci ## Footnote Approximately 80% of group B streptococci are capable of growing in 6.5% salt broth; however, they do not hydrolyze esculin or grow in media containing 4% bile salts.

Answer 77

A. Group A and D (enterococcus) streptococci ## Footnote The PYR hydrolysis test is highly specifi c for group A streptococci and group D enterococci. The test detects the pyrrolidonylarylamidase enzyme, which hydrolyzes PYR.

Answer 78

B. 240 Todd units

Answer 79

C. 320 Todd units

Answer 80

D. Culture specimens in ambient oxygen at 37°C ## Footnote MTM, New York City, and Martin–Lewis agars contain blood factors needed to support the growth of N. gonorrhoeae as well as antibiotics that prevent growth of normal genital flora. Cultures must be incubated in 3%–7% CO2 at 35°C. Cultures should be held a minimum of 48 hours before being considered negative.

Answer 81

A. Neisseria gonorrhoeae ## Footnote Specimens for culture of N. gonorrhoeae are best if plated immediately or transported in a medium containing activated charcoal to absorb inhibitory substances that hinder their recovery.

Answer 82

A. Neisseria gonorrhoeae

Answer 83

B. Neisseria elongata

Answer 84

D. Moraxella catarrhalis

Answer 85

B. Beta-lactamase ## Footnote Antimicrobial resistance in Neisseria gonorrhea is widespread. The production of betalactamase (penicillinase) breaks open the beta lactam ring of penicillin, destroying its activity. Thus, N. gonorrhoeae that produces beta lactamase are resistant to penicillin.

Answer 86

B. Oxidase positive and glucose positive, maltose negative ## Footnote Neisseria gonorrhoeae is oxidase positive and ferments glucose but not maltose

Answer 87

C. Enterobacteriaceae from gastrointestinal specimens ## Footnote XLD agar is selective for gram-negative coliforms because of a high concentration (0.25%) of deoxycholate, which inhibits gram-positive bacteria. In addition, XLD is differential for Shigella and Salmonella spp. The medium contains xylose, lactose, and sucrose, which are fermented by most normal intestinal coliforms producing yellow colonies. Shigella does not ferment the sugars and produces red (or clear) colonies. Salmonella spp. ferment xylose; however, they also decarboxylate lysine in the medium, causing production of ammonia. Therefore, Salmonella first appear yellow but become red. Some Salmonella produce hydrogen sulfi de (H2S) from sodium thiosulfate and therefore appear as red colonies with black centers.

Answer 88

C. MacConkey agar with sorbitol ## Footnote E. coli 0157:H7 ferments lactose, and therefore, appears as dark pink colonies on MacConkey agar. To differentiate E. coli 0157:H7 from normal fecal flora, MacConkey agar with sorbitol is used. E. coli 0157:H7 does not ferment sorbitol, and usually are colorless colonies.

Answer 89

A. Ferment glucose, reduce nitrate to nitrite, and are oxidase negative ## Footnote All Enterobacteriaceae ferment glucose and are oxidase negative and nonsporulating. Most Enterobacteriaceae are motile, but the genera Shigella and Klebsiella are not.

Answer 90

A. Acetoin ## Footnote Acetoin or acetylcarbinol, an end product of glucose fermentation, is converted to diacetyl after the addition of the VP reagents (α-naphthol and 40% potassium hydroxide [KOH]). Diacetyl is seen as a red- to pink-colored complex

Answer 91

D. 4.5 ## Footnote Both MR and VP tests detect acid production from the fermentation of glucose. However, a positive MR test denotes a more complete catabolism of glucose to highly acidic end products such as formate and acetate than occurs with organisms that are VP positive only (e.g., Klebsiella pneumoniae).

Answer 92

A. Blue color in the medium after 24 hours of incubation at 35°C ## Footnote The Simmons citrate test determines if an organism can utilize citrate as the sole source of carbon. The medium turns blue, indicating the presence of alkaline products such as carbonate. Tubes are incubated a minimum of 24 hours at 35°C with a loose cap before reading.

Answer 93

A. p Dimethylamino benzaldehyde ## Footnote The indole test detects the conversion of tryptophan (present in the media) to indole by the enzyme tryptophanase. Indole is detected by the reaction with the aldehyde group of pdimethylaminobenzaldehyde (the active reagent in Kovac’s and Ehrlich’s reagents) in acid, forming a red complex.

Answer 94

C. Ornithine decarboxylase ## Footnote Putrescine is the amine product of the decarboxylation of ornithine.

Answer 95

B. Morganella, Providencia, and Proteus ## Footnote Phenylalanine deaminase oxidatively deaminates phenylalanine, forming phenylpyruvic acid. When a solution of ferric chloride is added, the iron reacts with phenylpyruvic acid, forming a green-colored complex. Phenylalanine deaminase is found in the genera Morganella, Providencia, and Proteus and is an excellent test to determine if an organism belongs to this group. Rarely, isolates of Enterobacter may be phenylalanine deaminase positive as well.

Answer 96

B. Escherichia, Salmonella, Shigella, and Yersinia ## Footnote Escherichia, Salmonella, Shigella, and Yersinia are responsible for the majority of enteric diarrhea cases attributable to the Enterobacteriaceae family.

Answer 97

A. Shigella, Klebsiella, and Yersinia ## Footnote Shigella spp. and Klebsiella spp. are for the most part nonmotile. Yersinia can be motile at 22°C but is nonmotile at 36°C.

Answer 98

A. Campylobacter spp. ## Footnote Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.

Answer 99

B. Examined for the presence of Campylobacter sp. ## Footnote Campylobacter continues to be the most common enteric pathogen isolated from patients with diarrhea. Routinely fecal specimens should be cultured for Salmonella, Shigella and Campylobacter. Fecal specimens are not routinely cultured for enterotoxaemia E. coli or C. outline. E. Hartman is a non-pathogenic parasite and does not cause diarrhea.

Answer 100

D. Yersinia enterocolitica ## Footnote Cold enrichment is especially useful when specimens contain large numbers of normal flora that are sensitive to prolonged exposure to near-freezing temperature. In addition to Yersinia, the technique has been used to enhance recovery of Listeria monocytogenes from specimens containing other bacteria.

Answer 101

B. Escherichia coli ## Footnote More than 80% of uncomplicated UTIs are caused by Escherichia coli

Answer 102

D. Shigella ## Footnote Shigella is lactose negative, most species do not produce gas, are VP, urea, lysine decarboxylase and citrate negative, and they are non motile.

Answer 103

B. Escherichia coli ## Footnote E. coli can produce several different types of toxins that result in different gastroenteritis and manifestations.

Answer 104

D. Yersinia pestis ## Footnote Yersinia pestis is classically described as having a “safety pin” appearance on Wayson’s stain. This patient’s presentation is classic for bubonic plague.

Answer 105

A. Yellow pigmentation and negative sorbitol fermentation ## Footnote E. sakazakii is called a yellow-pigmented E. cloacae and is best differentiated from E. cloacae by sorbitol fermentation (95% positive for E. cloacae and 0% for E. sakazakii). In addition, E. cloacae is usually positive for urease and malonate (65% and 75%, respectively) and E. sakazakii is usually negative (1% and <20%, respectively). Both species are usually motile and arginine dihydrolase positive.

Answer 106

D. Indole ## Footnote K. oxytoca and K. pneumoniae are almost identical biochemically except for the ability to produce indole. Both organisms are usually positive for urease, sucrose, and citrate. However, K. oxytoca is indole positive and K. pneumoniae is indole negative.

Answer 107

B. Escherichia coli ## Footnote Strains of E. coli that produce one or both of the Shiga-like toxins (SLT I and SLT II) can cause bloody diarrhea (hemorrhagic colitis). In the United States, E. coli strain O157:H7 is the serotype most often associated with hemorrhagic colitis.

Answer 108

B. Serratia marcescens ## Footnote S. marcescens has been implicated in numerous nosocomial infections and is recognized as an important pathogen with invasive properties. Gelatin hydrolysis and DNase are positive for both the Proteus spp. and Serratia, but the negative urease and phenylalanine deaminase are differential.

Answer 109

A. Proteus vulgaris ## Footnote Although P. mirabilis is more frequently recovered from patients with urinary tract infections, P. vulgaris is commonly recovered from immunosuppressed patients. P. mirabilis is indole negative and ornithine decarboxylase positive but otherwise is very similar to P. vulgaris.

Answer 110

A. It is oxidase positive ## Footnote Enterobacteriaceae ferments glucose and are oxidase negative. . Pleisomonas was a member of the Vibrio family in part because it is oxidase positive. However it was moved to the Enterobacteriaceae despite its positive oxidase reaction.

Answer 111

D. Mannitol, nitrate reduction, growth at 42°C ## Footnote Pseudomonas aeruginosa: Positive for mannitol, nitrate reduction and growth at 42C Pseudomonas putida: Negative for mannitol, nitrate reduction and growth at 42C

Answer 112

B. P. aeruginosa ## Footnote P. aeruginosa is often recovered from the respiratory secretions of cystic fibrosis patients. If the patient is chronically infected with the mucoid strain of P. aeruginosa, the biochemical identifi cation is very diffi cult. The mucoid strain results from production of large amounts of alginate, a polysaccharide that surrounds the cell.

Answer 113

D. P. aeruginosa ## Footnote P. aeruginosa is highly resistant to many antimicrobial drugs as well as being one of the most often cultured opportunistic organisms. This virulence factor allows for many nosocomial infections such as those of the urinary tract, wounds (burn patients), bacteremia, respiratory tract, and CNS.

Answer 114

D. Burkholderia pseudomallei ## Footnote B. pseudomallei produces wrinkled colonies resembling P. stutzeri. Infections are usually asymptomatic and can be diagnosed only by serological methods. The organism exists in soil and water in an area of latitude 20° north and south of the equator (mainly in Thailand and Vietnam). Thousands of U.S. military personnel were infected with these bacteria during the 1960s and 1970s. The disease may reactivate many years after exposure and has been called the “Vietnamese time bomb.”

Answer 115

B. Pseudomonas aeruginosa ## Footnote Cetrimide (acetyl trimethyl ammonium bromide) agar is used for the isolation and identification of P. aeruginosa. With the exception of P. fluorescens, the other pseudomonads are inhibited along with related nonfermentative bacteria.

Answer 116

D. Thiosulfate citrate bile salts sucrose for Vibrio species ## Footnote Thiosulfate citrate bile salts agar is a selective media for Vibrio and it also differentiates sucrose fermenting species such as V. cholerae and V. alginolyticus.

Answer 117

A. Pure culture of Vibrio cholerae

Answer 118

A. Subculture the bottle, and incubate in microaerophilic conditions ## Footnote Campylobacter are gram negative, curved bacilli that require microaerophilic conditions for growth.

Answer 119

A. 5% O2, 10% CO2, and 85% N2

Answer 120

A. Urea broth ## Footnote Helicobacter pylori produce large amounts of extracellular urease and are positive for urea within 2 hours.

Answer 121

D. Urease, nitrate, and hippurate hydrolysis ## Footnote H. pylori: positive for urease; negative for nitrate reduction and hippurate hydrolysis C. jejuni: negative for urease; positive for nitrate reduction and hippurate hydrolysis

Answer 122

B. Pasteurella spp. ## Footnote Pasteurella multocida (P. canis) is part of the normal mouth flora of cats and dogs and is frequently recovered from wounds infl icted by them. It produces large amounts of indole and therefore an odor resembling colonies of E. coli. Pseudomonas spp. are also catalase and oxidase positive but can be ruled out because they grow on MacConkey agar and do not produce indole.

Answer 123

C. Cysteine and cystine ## Footnote F. tularensis is a fastidious gram-negative rod that is best recovered from lymph node aspirates and tissue biopsies. It is oxidase negative, nonmotile, and inert biochemically. Cysteine blood agar is the medium of choice, but F. tularensis will grow on commercially prepared chocolate agar because it contains X factor and is supplemented with a growth enrichment (IsoVitaleX) that contains cysteine. F. tularensis may not grow well on MacConkey agar.

Answer 124

B. Horse blood agar and Mueller–Hinton agar with X and V strips ## Footnote Production of β-hemolysis is used to distinguish these two species from other Haemophilus with the same X and V requirements. Horse blood agar furnishes X factor and, when supplemented with yeast extract, supports the growth of Haemophilus spp. Sheep blood agar is not used because it contains growth inhibitors for some Haemophilus spp.

Answer 125

B. H. ducreyi ## Footnote H. ducreyi requires exogenous X factor and causes genital lesions referred to as “soft chancres.”

Answer 126

D. H. influenzae

Answer 127

C. Gardnerella vaginalis

Answer 128

C. Legionella pneumophila

Answer 129

A. Legionella pneumophila ## Footnote L. pneumophila is the cause of pneumonia and can occur as part of an epidemic sporadically or nosocomially, or may be community acquired. The appearance of mottled, cut-glass colonies on buffered CYE agar under low power and the use of a direct immunofluorescence technique on sputum samples determine the presence of L. pneumophila. The most common environmental sites for recovery are shower heads, faucets, water tanks, and air-conditioning systems.

Answer 130

C. Proteus spp.

Answer 131

D. Pseudomonas aeruginosa

Answer 132

B. Pasteurella multocida

Answer 133

B. Chromobacterium violaceum

Answer 134

A. B. pertussis

Answer 135

C. B. bronchiseptica

Answer 136

B. B. parapertussis

Answer 137

B. Bacillus spp. ## Footnote The only spore former listed is the Bacillus spp., which grow as large, spreading colonies on blood agar plates. Pseudomonas spp. are gram-negative rods; Corynebacterium spp. appear as small, very dry colonies on BAP; Listeria spp. appear as very small β-hemolytic colonies on BAP, resembling Streptococcus species.

Answer 138

A. Motility and β-hemolysis on a blood agar plate ## Footnote Both species of Bacillus are catalase and lecithinase positive and produce acid from glucose. B. cereus is β-hemolytic and motile, but B. anthracis is neither.

Answer 139

A. Penicillin (10-unit) susceptibility test ## Footnote The best differentiating test to perform on a suspected B. anthracis culture is the 10-unit penicillin disk test. B. anthracis is susceptible but other Bacillus spp. are not.

Answer 140

D. Food ## Footnote The best specimen is the suspected food itself. Stool cultures are not useful because B. cereus is part of the normal fecal flora. The suspected food can be the source of food poisoning by B. cereus if 100,000 or greater organisms per gram of infected food are demonstrated.

Answer 141

D. C. perfringens ## Footnote Wounds infected with clostridia are characterized by invasion and liquefactive necrosis of muscle tissue with gas formation. The most frequent isolate is C. perfringens followed by C. novyi and C. septicum.

Answer 142

C. Clostridium perfringens ## Footnote C. perfringens produces a double zone of β-hemolysis on blood agar, which makes identification relatively easy. The inner zone of complete hemolysis is caused by a θ-toxin and the outer zone of incomplete hemolysis is caused by an α-toxin (lecithinase activity). The Bacteroides spp. are gram-negative bacilli, and C. diffi cile is lecithinase negative and does not produce a double zone of β-hemolysis.

Answer 143

A. Lecithinase ## Footnote Egg yolk agar (modifi ed McClung’s or neomycin egg yolk agar) is used to determine the presence of lecithinase activity, which causes an insoluble, opaque, whitish precipitate within the agar. Lipase activity is indicated by an iridescent sheen or pearly layer on the surface of the agar.

Answer 144

D. All of these options ## Footnote LIPASE + C. botulinum, C. sporogenes and C. novyi. Lipase is produced by some Clostridium spp. and is seen as an iridescent pearly layer on the surface of the colonies that extends onto the surface of the egg yolk agar medium surrounding them. C. perfringens, the most frequently isolated Clostridium species, is negative for lipase production.

Answer 145

B. Preformed toxin in food ## Footnote Foodborne botulism in adults and children is caused by ingestion of the preformed toxin (botulinum toxins A, B, E, and F) in food. The neurotoxins of C. botulinum are protoplastic proteins made during the growing phase and released during lysis of the organisms. Confirmation of botulism is made by demonstration of the toxin in serum, gastric, or stool specimens.

Answer 146

A. Ingestion of spores in food or liquid ## Footnote Epidemiological studies have demonstrated that infant botulism results from the ingestion of spores via breastfeeding or exposure to honey. Preformed toxin has not been detected in food or liquids taken by the infants. C. botulinum multiplies in the gut of the infant and produces the neurotoxin in situ.

Answer 147

A. Toxin neutralization ## Footnote Definitive identification of C. botulinum is made by the toxin neutralization test for its neurotoxins in serum or feces.

Answer 148

A. Round, terminal spores ## Footnote Spore appearance and location, along with Gram stain morphology, aids in distinguishing the Clostridium spp. Round, terminal spores are demonstrated when C. tetani is grown in chopped meat with glucose broth. Recognition of spores is particularly important because C. tetani sometimes appears as gram negative.

Answer 149

D. Clinical findings ## Footnote The culture and Gram stain of the puncture wound site usually does not produce any evidence of C. tetani. The diagnosis is usually based upon clinical findings, which are characterized by spastic muscle contractions, lockjaw, and backward arching of the back caused by muscle contraction.

Answer 150

B. C. difficile ## Footnote C. diffi cile is also implicated in hospital acquired diarrhea and colitis. Clinical testing for C. difficile includes culture and cytotoxin testing. Because culture takes 3 days and will detect nontoxigenic strains that do not cause diarrheal disease, immunoassays using antibodies against either the A toxin or both the A and B toxins are most frequently employed.

Answer 151

D. Clostridium difficile ## Footnote CCFA is used for recovery of C. diffi cile from stool cultures. Cycloserine and cefoxitin inhibit growth of gram-negative coliforms in the stool specimen. C. difficile ferments fructose, forming acid that, in the presence of neutral red, causes the colonies to become yellow.

Answer 152

B. Gas–liquid chromatography (GLC) ## Footnote Anaerobic bacteria can be identified by analysis of metabolic products using gas–liquid chromatography. Results are evaluated along with Gram staining characteristics, spore formation, and cellular morphology in order to make the identification

Answer 153

C. Corynebacterium diphtheriae ## Footnote C. diphtheriae must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area. A flexible calcium alginate nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.

Answer 154

A. Corynebacterium spp. ## Footnote Corynebacterium spp. are part of the normal upper respiratory tract flora. Organisms display typical pleomorphic shapes often resembling letters such as Y or L, and metachromatic granules. Identification of C. diphtheriae, however, requires selective culture media and biochemical testing.

Answer 155

C. Tinsdale medium ## Footnote Corynebacterium will grow on blood and chocolate agars, but Tinsdale agar is the preferred culture medium because the potassium tellurite in the agar causes C. diphtheriae to produce brown colonies surrounded by a brown halo. The halo effect is seen with C. diphtheriae, C. ulcerans, and C. pseudotuberculosis but not with other Corynebacterium or with other pigmented colonies growing on Tinsdale agar.

Answer 156

C. A positive toxigenicity test ## Footnote In order to determine if an isolate of Corynebacterium diphtheriae produces toxin, testing for the presence of diphtheria toxin must be performed using methods such as Elek test or PCR.

Answer 157

A. Gram stain, motility at room temperature, catalase ## Footnote *Streptococci Gram positive cocci in chains Nonmotile Catalase negative *Listeria Gram positive bacilli Motile Catalase positive

Answer 158

C. Erysipelothrix rhusiopathiae ## Footnote E. rhusiopathiae is catalase negative, whereas the other three organisms are catalase positive. E. rhusiopathiae is seen primarily as a skin infection on the fingers of meat and poultry workers. Colonies growing on blood agar are small and transparent, may be either smooth or rough, and are often surrounded by a green tinge. E. rhusiopathiae is characterized by H2S production in the butt of a TSI slant, which differentiates it from other catalase-negative, gram-positive rods.

Answer 159

A. Lactobacillus spp. ## Footnote Lactobacillus spp. produce both long, slender rods or short coccobacilli that form chains. Lactobacillus spp. are part of the normal flora of the vagina (are not considered a pathogen) and are sometimes confused with the streptococci.

Answer 160

A. Actinomyces israelii ## Footnote A. israelii is part of the normal flora of the mouth and tonsils but may cause upper or lower respiratory tract infections. The sulfur granules are granular microcolonies with a purulent exudate

Answer 161

B. Nocardia spp. ## Footnote Nocardia spp. should be suspected if colonies that are partially acid fast by the traditional method are positive with the modifi ed acid-fast method using Kinyoun stain and 1% sulfuric acid as the decolorizing agent. The other organisms listed are negative for acid fast stain.

Answer 162

D. Nocardia spp. ## Footnote All of the listed organisms produce mycelium (aerial or substrate), causing them to appear branched when Gram stained, but only the Nocardia spp. are positive for modified acid fast stain. Nocardia is an opportunistic pathogen, and cultures typically have a musty basement odor.

Answer 163

D. Nocardia asteroides ## Footnote Nocarida asteroides are partially acid fast and do not hydrolyze the substrates casein, tyrosine or xanthine.

Answer 164

A. Bright red rods against a blue background ## Footnote The carbolfuchsin (fuchsin with phenol) stains the mycobacteria red and does not decolorize after the acid–alcohol is added. The background and any other bacterial elements will decolorize and are counterstained blue by the methylene blue.

Answer 165

C. Petragnani’s agar ## Footnote All four media contain malachite green as an inhibitory agent of nonmycobacteria, but Petragnani’s medium contains a higher concentration (0.052 g/dL) than Löwenstein– Jensen (0.025 g/dL), Middlebrook 7H10 (0.0025 g/dL), or American Thoracic Society medium (0.02 g/dL). The last is used for normally sterile specimens, such as from CSF and bone marrow.

Answer 166

B. Rejected ## Footnote Specimens submitted for culture and recovery of any bacteria should be submitted without fixatives.

Answer 167

B. M. tuberculosis ## Footnote Niacin production is common to all mycobacteria. However, the niacin accumulates as a water-soluble metabolite in the culture medium when the organism cannot form niacin ribonucleotide. M. tuberculosis, M. simiae, and some strains of M. marinum, M. chelonae, and M. bovis lack the enzyme and therefore are called niacin positive because of the accumulation of niacin detected in the test medium.

Answer 168

A. Mycobacterium tuberculosis ## Footnote M. tuberculosis is positive for niacin accumulation, while the other three species are niacin negative. A serpentine pattern of growth indicates production of cording factor, a virulence factor for M. tuberculosis.

Answer 169

D. Mycobacterium bovis ## Footnote M. bovis is also called the bovine tubercle bacillus. A nonvirulent strain, bacillus Calmette– Guérin (BCG), is used as a tuberculosis vaccine throughout the world. Infections with M. bovis resemble infections caused by M. tuberculosis and are seen in circumstances where there is close contact between humans and cattle.

Answer 170

A. M. bovis ## Footnote M. bovis and M. tuberculosis are very similar biochemically, and some strains of M. bovis also accumulate niacin. The T2H test differentiates M. tuberculosis from M. bovis. M. tuberculosis is not inhibited by T2H

Answer 171

C. M. kansasii ## Footnote M. kansasii hydrolyses Tween 80 more rapidly than the other species (within 3–6 hours).

Answer 172

A. M. avium ## Footnote More than 90% of MAC organisms that are isolated from AIDS patients are M. avium. These are distinguished from M. intraceulluare by NATs.

Answer 173

D. M. gordonae ## Footnote M. gordonae is a nonpathogen, scotochromogen, and rapid grower (7 days at 37°C). Rarely, it is implicated in opportunistic infections in patients with shunts, prosthetic heart values, or hepatoperitoneal disease. The other three species are pathogenic mycobacteria.

Answer 174

B. M. paratuberculosis ## Footnote M. paratuberculosis is known to cause an ulcerative intestinal disease with chronic diarrhea in cattle known as Johne’s disease. While M. paratuberculosis has been isolated from the intestines of humans with Crohn’s disease, the organism has not yet been proven to cause ileitis in humans.

Answer 175

A. M. leprae ## Footnote M. leprae and M. microti are different from all other mycobacteria because they cannot be cultured in vitro. Biopsies from nodules and plaques of skin that show numerous AFB are presumptively diagnosed as positive for M. leprae. Confirmatory identification is made by nucleic acid testing (NAT) using PCR.

Answer 176

A. M. chelonae–fortuitum complex ## Footnote Mycobacteria growing on MacConkey agar are usually nonpathogens. M. chelonae and M. fortuitum are both nonpathogenic rapid growers that will grow on MacConkey agar (with no crystal violet) within 5 days.

Answer 177

A. Borrelia spp. ## Footnote Borrelia spp. are often seen on Wright’s-stained smears of peripheral blood as helical bacteria with 3–10 loose coils. They are gram negative but stain well with Giemsa’s stain.

Answer 178

D. Borrelia burgdorferi ## Footnote Lyme disease may result in acute arthritis and meningitis and is caused by B. burgdorferi.

Answer 179

A. Serology ## Footnote Serological analysis using immunofluorescence or an enzyme immunoassay is the method of choice for diagnosis of Lyme disease.

Answer 180

B. Serological analysis ## Footnote Serological tests of the patient’s serum for evidence of syphilis are routinely performed, but culturing is not because research animals must be used for inoculation of the suspected spirochete. T. pallidum does not stain by either the Gram or acid-fast technique.

Answer 181

A. Inoculate cycloheximide-treated McCoy cells ## Footnote Chlamydiae are strict intracellular organisms and must be cultured using living cells. Direct smears can also be made at the time of culture. Staining cells with iodine may reveal the characteristic reddish-brown inclusions sometimes seen in Chlamydia infections. Fluorescein-conjugated monoclonal antibodies may be used to identify the organisms in infected cells.

Answer 182

B. PCR molecular testing ## Footnote PCR is both sensitive and specific and may be performed on urine.

Answer 183

B. Mycoplasma pneumoniae ## Footnote A common cause of respiratory tract illness, M. pneumoniae, generally causes a self limited infection (3–10 days) and usually does not require antibiotic therapy. M. pneumoniae can be cultured from the upper and lower respiratory tracts onto specially enriched (diphasic) media, but is most frequently diagnosed by the change in antibody titer from acute to convalescent serum using enzyme immunoassay or other serological methods.

Answer 184

A. Mycoplasma hominis ## Footnote Genital mycoplasmas (M. hominis and Ureaplasma urealyticum) are grown on specific agars. M. hominis is grown on “M” agar containing arginine and phenol red. Colonies of mycoplasma are 50–300 μm in diameter and display a “fried-egg” appearance with red holes.

Answer 185

A. EIA testing and direct antigen testing ## Footnote Adults may fail to produce an IgM response especially in recurrent infections, so the best confirmatory approach is a combination of EIA and direct antigen testing.

Answer 186

B. Ureaplasma urealyticum ## Footnote U. urealyticum is the only human mycoplasma that hydrolyzes urea. The manganous chloride–urea test utilizes manganous chloride (MnCl2) in the presence of urea. Urease produced by the organism hydrolyzes the urea to ammonia. This reacts with MnCl2 forming manganese oxide, which is insoluble and forms a dark brown precipitate around the colonies. The reaction is observed under a dissecting microscope and is a rapid test for the identifi cation of U. urealyticum.

Answer 187

D. Ehrlichia and Anaplasma spp. ## Footnote Ehrlichia and Anaplasma spp. are intracellular bacteria and are the causative agents of human monocytotropic ehrlichiosis (HME) and human granulocytotropic anaplasmosis (HGA). The organisms infect humans, dogs, and cattle through the bite of an infected Ixodes tick which also transmits Borrelia spp., causing Lyme disease.

Answer 188

A. Skin ## Footnote A solution of 10% KOH is used for contaminated specimens such as skin, nail scrapings, hair, and sputum to clear away background debris that may resemble fungal elements. Normally sterile specimens (CSF, blood, and bone marrow) do not require KOH for clearing.

Answer 189

A. Sepedonium spp. ## Footnote Sepedonium spp. are saprophytic molds that do not have a yeast phase and produce large spherical tuberculate macroconidia like H. capsulatum. Histoplasmosis is a chronic granulomatous infection primarily found in the lungs that invades the reticuloendothelial system. Infection occurs via spores released from decaying bird or chicken droppings that are inhaled when disturbed.

Answer 190

D. Production of germ tubes ## Footnote Essentially all strains of Candida albicans produce germ tubes within 2 hours of incubation at 37°C in serum.

Answer 191

D. C. albicans, C. dubliniensis

Answer 192

D. Sporothrix ## Footnote Sporothrix is the sole member of the list that does not produce arthroconidia.

Answer 193

B. Phenol oxidase ## Footnote Phenol oxidase breaks down the substrate found in niger seeds producing melanin. This result is characteristic of C. neoformans.

Answer 194

C. 30°C; 21 days

Answer 195

B. Zygomycetes

Answer 196

A. Malassezia furfur ## Footnote M. furfur has a worldwide distribution and causes a superficial, brownish, dry, scaly patch on the skin of light-skinned persons and lighter patches on persons with dark skin.

Answer 197

A. Dermatophytes (tinea)

Answer 198

C. Microsporum audouinii ## Footnote Historically, the differentiation of dermatophytes was accomplished using a variety of morphologic characteristics and growth characteristics. The characteristics listed support the identification of Microsporum audouinii. The most suggestive of these characteristics is the rare distorted macroco- nidia and rare microconidia.

Answer 199

A. T. mentagrophytes and T. rubrum ## Footnote T. mentagrophytes may produce a deep red pigment seen through the reverse side of the agar plate that resembles the cherry-red pigment produced by T. rubrum. However, T. mentagrophytes can be differentiated by its ability to invade the hair shaft. T. rubrum grows on the surface of the hair but does not penetrate the shaft.

Answer 200

A. Chromoblastomycosis

Answer 201

A. Histoplasma capsulatum

Answer 202

B. Blastomyces dermatitidis ## Footnote Blastomyces dermatitidis is endemic to North America, specifi cally the Mississippi river valley. When seen in tissue samples it appears as large, spherical, thick-walled yeast cells 8 to 15 um in diameter, usually with a single bud that is connected to the parent cell by a broad base.

Answer 203

A. Paracoccidioides brasiliensis ## Footnote P. brasiliensis yeast forms are sometimes seen as a “mariner’s wheel” because multiple budding cells completely surround the periphery of the parent cell.

Answer 204

C. Produces endosporulating spherules in tissue ## Footnote Coccidioides immitis is endemic in hot, semi-arid climates such as the southwestern United States and northern Mexico. It is a saprobe in mold form (desert soil). It is the most virulent of all agents of human mycoses. Coccidioides causes mild infection in everyone who inhales it, but is usually asymptomatic and self-limiting. Dissemination in the immunocompromised population is much higher than found for other fungal agents. The part of its life cycle in the mammalian host is highlighted by the endosporulating spherules in tissue.

Answer 205

B. Candida albicans

Answer 206

B. Cryptococcus neoformans ## Footnote Immunocompromised patients are at risk for invasion of Cryptococcus neoformans. The polysaccharide capsule of C. neoformans is not recognized by phagocytes, which allow patients with impaired cell-mediated immunity to become readily infected with C. neoformans.

Answer 207

D. Positive niger seed agar test ## Footnote Cryptococcus neoformans can be differentiated from other Cryptococcus species through the use of the Niger seed test; C. neoformans is Niger seed–positive (dark colonies).

Answer 208

C. Nucleic acid composition ## Footnote True viruses have nucleic acid that is either RNA or DNA, and this serves as the basis for initial classification. Members of these classes are further divided into groups that cause human disease based upon the mode of transmission, tissues invaded, diseases produced, and antigenic characteristics.

Answer 209

A. Respiratory syncytial virus (RSV) ## Footnote RSV is the cause of croup, bronchitis, bronchiolitis, and interstitial pneumonia. Children under 1 year old who are hospitalized are the most susceptible group.

Answer 210

D. Coxsackie B virus ## Footnote Coxsackie A virus, Coxsackie B virus, and the echoviruses are most commonly implicated in myocarditis and other syndromes, including acute cerebellar ataxia and hepatitis. Like poliovirus, infections are more common in the summer and fall and gain entry through the gastrointestinal tract.

Answer 211

A. Cytomegalovirus (CMV) ## Footnote CMV infection in a previously healthy individual causes a self-limited mononucleosis syndrome. CMV is an opportunistic pathogen that may produce lifelong infections and can cause a variety of diseases, including congenital and neonatal infection, hepatitis, pneumonia, and disseminated infection in immunocompromised patients.

Answer 212

B. Rotavirus ## Footnote Rotaviruses have been implicated in both nosocomial infections and epidemic gastroenteritis. Children 3–24 months old are most commonly affected. Diarrhea begins after an incubation period of 3 days, lasts for 2–10 days, and is associated with vomiting and dehydration. In immunosuppressed children, rotavirus causes a chronic infection.

Answer 213

D. Parvovirus B19 ## Footnote Parvovirus causes a fever and characteristic “slapped cheek” rash in young children. Adults are usually immune, but immunocompromised persons may exhibit an arthritis or anemia (the virus infects immature RBCs in the bone marrow).

Answer 214

D. All of these options

Answer 215

A. HBs Ag ## Footnote Hepatitis B surface antigen (HBsAg) is the first marker to appear in hepatitis B virus infection. It is usually detected within 4 weeks of exposure (prior to the rise in transaminases) and persists for about 3 months after serum enzyme levels return to normal.

Answer 216

B. Anti-HBc IgM ## Footnote Antibody to the hepatitis B core antigen (anti-HBc) is the first detectable hepatitis B antibody. It persists in the serum for 1–2 years postinfection and is found in the serum of asymptomatic carriers of HBV. Because levels of total anti-HBc are high after recovery, IgM anti-HBc is a more useful marker for acute infection. Both anti-HBc and anti-HBs can persist for life, but only anti-HBs is considered protective.

Answer 217

D. Anti-HBs ## Footnote Anti-HBs appears later in infection than anti-HBc and is used as a marker for immunity following infection or vaccination rather than for diagnosis of current infection.

Answer 218

B. Varicella-zoster virus ## Footnote Varicella-zoster virus is the cause of an infection with chickenpox. As an adult, the father is experiencing shingles, a reactivation of the virus. The virus lies dormant in the sensory (dorsal root) ganglia of the spinal nerves, and its reactivation produces a nonweeping blisterlike rash on an inflamed skin base that follows the path of the underlying nerves.

Answer 219

A. BK virus—urine ## Footnote The BK virus, a polyoma virus, is transmitted by direct contact with infected respiratory secretions. It has tropism for the urinary system, and often causes a latent, asymptomatic infection in the kidney. However, in immunocompromised patients, the virus is often implicated in renal and bladder infections. Kidney failure caused by BK virus is a significant concern in bone marrow and renal transplant recipients.

Answer 220

B. Measles ## Footnote Koplik spots are diagnostic for measles infection and represent necrotic vesicles with a white center surrounded by erythema.

Answer 221

D. Human herpes virus 8 ## Footnote Kaposi sarcoma, a relatively common cancer in patients with AIDS, has been linked to human herpes virus 8.

Answer 222

D. Rabies virus ## Footnote Rabies is a neurotropic virus that causes extensive destruction in the brain. Negri bodies are seen in the cytoplasm of large ganglion cells and are demonstrated by Seller's stain. Rabies in humans or lower animals can be diagnosed by demonstration of these characteristic inclusions.

Answer 223

D. Papillomavirus ## Footnote The etiologic agents for the numerous benign cutaneous and mucosal lesions known as warts are the human papillomaviruses (HPVs).

Answer 224

B. HSV and VZV

Answer 225

A. Parvovirus B19

Answer 226

D. Marburg virus

Answer 227

A. Measles virus ## Footnote Subacute sclerosing panencephalitis (defective measles virus infection of CNS).

Answer 228

C. Enterovirus

Answer 229

A. Cytomegalovirus (CMV) ## Footnote CMV infection in a previously healthy individual causes a self-limited mononucleosis syndrome.

Answer 230

D. Parvovirus B19 ## Footnote Parvovirus causes a fever and characteristic “slapped cheek” rash in young children. Adults are usually immune, but immunocompromised persons may exhibit an arthritis or anemia (the virus infects immature RBCs in the bone marrow).

Answer 231

C. Noroviruses ## Footnote Norovirus is an important cause of gastroenteritis in several settings, including closed environments such as cruise ships and long-term care facilities. None of the other viruses listed are associated with gastroenteritis as a major symptom.

Answer 232

B. Coronavirus ## Footnote The severe acute respiratory syndrome (SARS) virus arose as a previously unrecognized organism causing serious respiratory tract infections. This virus has been shown to be part of the coronavirus group.

Answer 233

C. Coronaviruses ## Footnote This is the description of the coronavirus group.

Answer 234

D. Feces sample ## Footnote Rotaviruses are responsible for significant out- breaks of gastroenteritis and are an enteric virus. The specimen of choice for detecting this virus is stool.

Answer 235

B. PCR ## Footnote Nucleic amplification assays such as polymerase chain reaction are the most sensitive method for the detection of many/most viruses and patient samples, including cerebrospinal fluid for the diagnosis of meningitis.

Answer 236

A. #0.5 McFarland standard

Answer 237

C. 1% sulfuric acid and 1.175% barium chloride

Answer 238

B. BSC Class II, A1

Answer 239

C. BSC Class II, B1

Answer 240

D. BSC Class II, B2

Answer 241

E. Elimination

Answer 242

Grow toward the top of the broth

Answer 243

Microareophilic organisms

Answer 244

Vancomycin

Answer 245

Erythromycin

Answer 246

Proteus mirabilis

Answer 247

Nylon ## Footnote NYLON STRANDS ARE SPRAYED OR FLOCKED ONTO THE TIP.

Answer 248

Uses 15 lbs of pressure for 15 minutes ## Footnote he traditional gravity displacement of steam sterilization cycle is 121˚C for 15 minutes at 15 pounds per square inch. Ethylene dioxide is an alternative sterilization method.

Answer 249

Gram stain

Answer 250

Motility and H2S ## Footnote These 4 IMViC tests (actually 6 tests if you include motility and H2S) constitute, perhaps, the most critical tests used for identification of bacteria after the gram stain. The test results from these 6 tests should carry more weight than almost any other tests, certainly higher priority than sugar results since they are more stable reactions.

Answer 251

DCA ## Footnote Salmonella Shigella (SS) Agar is a modification of the Deoxycholate Citrate Agar

Answer 252

Buffering capacity was overcomed ## Footnote Some stool specimens may be highly acidic and will overcome the buffering capacity of the medium. This will cause the red indicator to shift to a yellow color. Discard the medium if it has turned yellow and request another specimen.

Answer 253

Microaerophilic organisms ## Footnote In addition to amount of growth present, the location of growth within thioglycollate broth indicates the type of organism present based on oxygen requirements. Strict anaerobes will grow at the bottom of the broth tube, whereas aerobes will grow near the surface. Microaerophilic organisms will grow slightly below the surface where oxygen concentrations are lower than atmospheric concentrations. In addition, facultative anaerobes and aerotolerant organisms will grow throughout the medium, as they are unaffected by the variation in oxygen content.

Answer 254

Urine for culture of acid-fast bacilli ## Footnote Urine is an appropriate specimen for the detection of renal tuberculosis. Since feces contain anaerobic organisms as part of the indigenous flora, it is an unacceptable specimen for anaerobic culture. Foley catheter tips are also not acceptable for culture because they are contaminated with colonizing organisms. Gram stain smears of rectal swabs for N. gonorrhoeae should also not be performed, since the presence of organisms with similar morphologies may lead to over interpretation of smears.

Answer 255

Aspirate urine aseptically from the catheter tubing ## Footnote Indwelling catheters are closed systems, and should not be disconnected for specimen collection. Urine samples should not be collected from catheter bags, and Foley catheter tips are unsuitable for culture because they are contaminated with colonizing organisms. Urine from indwelling catheters should be collected by aseptically puncturing the tubing (collection port).

Answer 256

1% sulfuric acid and 1.175% barium chloride

Answer 257

3 to 5 mm ## Footnote (average of 4 mm.)

Answer 258

The depth of the media was too thin

Answer 259

pH of Mueller-Hinton agar being too low ## Footnote Mueller-Hinton Agar used for disk diffusion is standardized at pH 7.2 to 7.4. Penicillin function better in an acidic environment, so zone sizes would become larger if the media pH is too low. Aminoglycosides, on the other hand are less effective in an acidic environment, so zone sizes would become smaller if the pH of the media is too low.

Answer 260

Decreased ## Footnote As it diffuses into the media, the concentration of antibiotic gets lower the further it diffuses from the disk.

Answer 261

Every week ## Footnote Daily disk diffusion quality control can be converted to weekly testing when 30 days of consecutive testing demonstrated no more than 3 antibiotic/ organism combinations outside the acceptable limits.

Answer 262

Pulsed-field gel electrophoresis ## Footnote The most commonly used method to determine the relatedness of 2 or more bacterial strains is pulsed-field gel electrophoresis.

Answer 263

S. agalactiae ## Footnote All of the organisms listed are potential causes of meningitis. Group B streptococcus is also associated with neonatal meningitis and meningitis of the elderly.

Answer 264

Vibrio cholerae ## Footnote The toxin produced by enterotoxigenic E. coli is similar in action and amino acid sequence to cholera toxin.

Answer 265

KCN, malonate, beta-galactosidase, lysine decarboxylase ## Footnote Salmonella are positive for lysine decarboxylase and most are negative for KCN, malonate and ONPG. Citrobacter are negative for lysine decarboxylase and positive for growth in KCN.

Answer 266

Yersinia pestis

Answer 267

Bordetella pertussis

Answer 268

Bordetella bronchiseptica ## Footnote Bordetella bronchiseptica are normal flora in the respiratory tract of various animals. A key reaction is that it is rapidly urea positive (within 4 hours). Brucella is also urea positive, but does not grow in MacConkey agar.

Answer 269

Aeromonas hydrophila ## Footnote Enterobacteriaceae, such as E. coli, Serratia and Enterobacter are oxidase negative. The only selection that is oxidase positive is Aeromonas. It is associated with wounds contaminated with water.

Answer 270

Thiosulfate citrate bile salts sucrose for Vibrio species ## Footnote Thiosulfate citrate bile salts agar is a selective media for Vibrio and it also differentiates sucrose fermenting species such as V. cholerae and V. alginolyticus.

Answer 271

Cary-Blair medium ## Footnote Stool specimens suspected of containing Vibrio spp. should be collected and transported only in Cary-Blair medium.

Answer 272

Haemophilus influenzae

Answer 273

Motility at 25C ## Footnote Corynebacterium and Listeria are catalase positive and gram positive bacilli. Listeria demonstrate “tumbling motility” that is best demonstrated following growth at 25˚C. A few species of Corynebacterium are motile when grown at 35˚C.

Answer 274

Catalase and spot indole ## Footnote Propionibacterium acnes is part of the normal flora on the skin and is a common blood culture contaminant. The gram stain given is typical for P. acnes, and it is catalase and indole positive.

Answer 275

Cryptococcus neoformans

Answer 276

Sporothrix schenckii

Answer 277

Aspergillus spp.

Answer 278

Humans ## Footnote Most often, humans are “dead-end” hosts, meaning that there is no subsequent human-tohuman transmission.

Answer 279

1: 2 to 1:5

Answer 280

Chromogenic cephalosporin

Answer 281

The swarming area should be ignored

Answer 282

Microtube broth dilution ## Footnote The anaerobes are not suited for the broth disk elution or disk agar diffusion tests because of their slow rate of growth. Kirby–Bauer method reference charts are not designed to be used as a reference of susceptibility for anaerobes.

Answer 283

Incubated at 37°C and cultured as soon as possible

Answer 284

Needle aspirate after surface decontamination

Answer 285

Urinary tract infections ## Footnote The incidence of anaerobic bacteria recovered from the urine is approximately 1% of isolates. The other three types of infection are associated with a 60%–93% incidence of anaerobic recovery. Urine is not cultured routinely under anaerobic conditions unless obtained surgically (e.g., suprapubic aspiration).

Answer 286

Bacteroides, Peptostreptococcus, and Clostridium spp. ## Footnote Anaerobic culture media can be prereduced before sterilization by boiling, saturation with oxygen-free gas, and addition of cysteine or other thiol compounds. The final oxidation reduction potential (Eh) of the medium should be approximately –150 mV to minimize the effects of exposure of organisms to oxygen during inoculation.

Answer 287

Kanamycin–vancomycin (KV) agar

Answer 288

Gas–liquid chromatography (GLC) ## Footnote Anaerobic bacteria can be identified by analysis of metabolic products using gas–liquid chromatography. Results are evaluated along with Gram staining characteristics, spore formation, and cellular morphology in order to make the identification.

Answer 289

Neisseria gonorrhoeae

Answer 290

Staphylococcus aureus

Answer 291

Staphylococcus aureus

Answer 292

S. intermedius

Answer 293

Vancomycin ## Footnote MRSA isolates are usually tested for susceptibility or resistance to vancomycin, a glycopeptide.

Answer 294

Oxacillin ## Footnote Oxacillin is the drug used to screen staphylococci for resistance to antibiotics having the β-lactam ring. Included in this group are penicillin, cephalosporin, monobactam, and carbapenem. MRSA defines strains of staph that are resistant to all of these antibiotic groups. MRSA strains are treated with vancomycin or oxazolidinone.

Answer 295

D-zone test

Answer 296

Mannitol salt agar

Answer 297

Facultative anaerobe, oxidase negative, catalase negative

Answer 298

Bacitracin, CAMP, PYR ## Footnote Group B streptococci (S. agalactiae) are important pathogens and can cause serious neonatal infections. Women who are found to be heavily colonized vaginally with S. agalactiae pose a threat to the newborn, especially within the first few days after delivery. The infection acquired by the infant is associated with pneumonia.

Answer 299

Streptococcus pneumoniae colonies on a blood agar plate

Answer 300

Staphylococcal cross-streak test

Answer 301

Culture specimens in ambient oxygen at 37°C ## Footnote Cultures must be incubated in 3%–7% CO2 at 35°C.

Answer 302

Neisseria gonorrhoeae

Answer 303

N. lactamica

Answer 304

Enterobacteriaceae

Answer 305

Enterobacteriaceae from gastrointestinal specimens

Answer 306

Shigella spp. from some strains of Escherichia coli

Answer 307

Ammonium carbonate ## Footnote The test for urease production is based on the ability of the colonies to hydrolyze urea in Stuart broth or Christensen agar to form CO2 and ammonia. These products form ammonium carbonate, resulting in alkalinization. This turns the pH indicator (phenol red) pink at pH 8.0.

Answer 308

p-Dimethylaminobenzaldehyde

Answer 309

Ornithine decarboxylase

Answer 310

Morganella, Providencia, and Proteus

Answer 311

Ferment glucose, reduce nitrate to nitrite, and are oxidase negative

Answer 312

Lactose, indole, ONPG, and motility ## Footnote E. coli, positive for lactose, indole, and ONPG are usually motile. Shigella species do not ferment lactose or produce indole, lack β-galactosidase, and are nonmotile.

Answer 313

Campylobacter spp. ## Footnote Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.

Answer 314

Morganella spp.

Answer 315

Yersinia pestis

Answer 316

E. coli O157:H7, Salmonella spp., Shigella spp.

Answer 317

Aminoglycosides, trimethoprim–sulfamethoxazole, third-generation cephalosporins

Answer 318

E. coli and Klebsiella pneumoniae

Answer 319

Oxidase, motility, NO3 reduction ## Footnote Acinetobacter spp. are nonmotile rods that appear as coccobacillary forms from clinical specimens. All are oxidase negative and catalase positive. P. aeruginosa reduces NO3 to NO2, while A. baumannii does not.

Answer 320

Burkholderia pseudomalleii

Answer 321

Pigment on blood agar, oxidase, DNase ## Footnote Both organisms produce yellowish pigment and have polar tuft flagella, but the oxidase and DNase tests are differential.

Answer 322

Urease (rapid) ## Footnote Alcaligenes and Bordetella are genera belonging to the Alcaligenaceae family. The two organisms are very similar biochemically, but B. bronchiseptica is urease positive. Both organisms are oxidase positive, grow on MacConkey agar, and are motile by peritrichous flagella. B. bronchiseptica grows well on MacConkey agar but other species of Bordetella are fastidious gram-negative rods.

Answer 323

Pseudomonas aeruginosa

Answer 324

P. aeruginosa

Answer 325

Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth

Answer 326

Aeromonas hydrophilia ## Footnote The oxidase positive test result rules out the members of the Enterobacteriaceae family.

Answer 327

Mannitol fermentation, Na+ requirement ## Footnote All three organisms are positive for oxidase production and are motile. Plesiomonas spp. do not grow on TCBS agar. Clear colonies on MacConkey agar and yellow colonies on TCBS agar indicate Vibrio or Aeromonas spp. However, only Vibrio spp. require Na+ (1% NaCl) in the medium for growth.

Answer 328

Oxidase ## Footnote Aeromonas growing on enteric media are differentiated from the Enterobacteriaceae by demonstrating that colonies are oxidase positive.

Answer 329

5% O2, 10% CO2, and 85% N2

Answer 330

Urease, nitrate, and hippurate hydrolysis

Answer 331

Pasteurella spp.

Answer 332

Francisella tularensis

Answer 333

Bartonella spp.

Answer 334

Chryseobacterium meningosepticum

Answer 335

Capnocytophaga canimorsus ## Footnote C. canimorsus are part of the oral flora of dogs. The organisms require at least 5% CO2 for growth and grow slowly on blood and chocolate agars. Colonies can grow in 48 hours if cultured in high CO2 on BHI agar with 5% sheep blood.

Answer 336

Direct immunofluorescent microscopy ## Footnote Since culture can take up to 10 days, rapid diagnosis by direct immunofluorescence and DNA amplification are preferred. Direct fluorescent antibody tests are not as sensitive as culture or PCR, but are specific and can be used to rapidly confirm a positive serological test, which may be positive in the absence of disease.

Answer 337

All of these options

Answer 338

Clinical findings ## Footnote The culture and Gram stain of the puncture wound site usually does not produce any evidence of C. tetani. The diagnosis is usually based upon clinical findings, which are characterized by spastic muscle contractions, lockjaw, and backward arching of the back caused by muscle contraction.

Answer 339

Clostridium difficile

Answer 340

Propionibacterium acnes ## Footnote P. acnes is a nonspore former and is described as a diphtheroid-shaped rod. It is part of the normal skin, nasopharynx, genitourinary, and gastrointestinal tract flora but is implicated as an occasional cause of endocarditis.

Answer 341

Corynebacterium diphtheriae

Answer 342

Mycobacterium tuberculosis ## Footnote M. tuberculosis is positive for niacin accumulation, while the other three species are niacin negative. A serpentine pattern of growth indicates production of cording factor, a virulence factor for M. tuberculosis.

Answer 343

Latently infected ## Footnote A positive PPD test indicates a person who is latently infected with M. tuberculosis. Such persons are asymptomatic and not infectious, but have a 10% risk of developing tuberculosis during their lifetime.

Answer 344

M. paratuberculosis

Answer 345

Serological analysis ## Footnote Serological tests of the patient’s serum for evidence of syphilis are routinely performed, but culturing is not because research animals must be used for inoculation of the suspected spirochete.

Answer 346

Mycoplasma hominis

Answer 347

Inoculate cycloheximide-treated McCoy cells

Answer 348

Ehrlichia and Anaplasma spp.

Answer 349

Germ tube test

Answer 350

T. mentagrophytes and T. rubrum

Answer 351

Cryptococcus neoformans

Answer 352

Coccidioides immitis

Answer 353

Antibiotics and nutrient ## Footnote Media used for transporting specimens for viral culture are similar to those for bacteria with the addition of a nutrient such as fetal calf serum or albumin and antibiotics.

Answer 354

Molecular technique and cell culture

Answer 355

Ribosomes ## Footnote Ribosomes, which are compact nucleoproteins, are composed of rRNA and proteins. They are central to translation, assisting with coupling of all required components and controlling the translational process.

Answer 356

Transformation ## Footnote Transformation involves recipient cell uptake of naked (free) DNA released into the environment when another bacterial cell (i.e., donor) dies and undergoes lysis. This genomic DNA exists as fragments in the environment. Certain bacteria are able to take up naked DNA from their surroundings; that is, they are able to undergo transformation. Such bacteria are said to be competent. Among the bacteria that cause human infections, competence is a characteristic commonly associated with members of the genera Haemophilus, Streptococcus, and Neisseria.

Answer 357

Transduction ## Footnote Transduction is mediated through viruses capable of infecting bacteria (i.e., bacteriophages).

Answer 358

Conjugation ## Footnote Conjugation occurs between two living cells, involves cell-to-cell contact, and requires mobilization of the donor bacterium’s chromosome.

Answer 359

Conjugation ## Footnote In addition to chromosomal DNA, genes encoded in extrachromosomal genetic elements, such as plasmids and transposons, may be transferred by conjugation. Not all plasmids are capable of conjugative transfer, but for those that are, the donor plasmid usually is replicated so that the donor retains a copy of the plasmid transferred to the recipient.

Answer 360

Single-celled prokaryotes ## Footnote Among clinically relevant organisms, bacteria are single-cell prokaryotic microorganisms. Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals. Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.

Answer 361

Not considered cellular organisms but rather infectious agents ## Footnote Among clinically relevant organisms, bacteria are single-cell prokaryotic microorganisms. Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals. Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.

Answer 362

Gram-positive bacteria ## Footnote The cell wall of gram-positive bacteria contains teichoic acids (i.e., glycerol or ribitol phosphate polymers combined with various sugars, amino acids, and amino sugars).

Answer 363

Gram-negative bacteria ## Footnote The periplasmic space typically is found only in gram-negative bacteria (whether it is present in gram-positive organisms is the subject of debate). The periplasmic space is bounded by the internal surface of the outer membrane and the external surface of the cellular membrane. This area, which contains the murein layer, consists of gel-like substances that assist in the capture of nutrients from the environment. This space also contains several enzymes involved in the degradation of macromolecules and detoxification of environmental solutes, including antibiotics that enter through the outer membrane.

Answer 364

Sterilization ## Footnote Sterilization is a process that kills all forms of microbial life, including bacterial spores. Disinfection is a process that destroys pathogenic organisms, but not necessarily all microorganisms or spores.

Answer 365

Disinfection ## Footnote Sterilization is a process that kills all forms of microbial life, including bacterial spores. Disinfection is a process that destroys pathogenic organisms, but not necessarily all microorganisms or spores.

Answer 366

Incineration ## Footnote Incineration is the most common method of treating infectious waste. Hazardous material is literally burned to ashes at temperatures of 870° to 980°C. Incineration is the safest method to ensure that no infective materials remain in samples or containers when disposed. Prions, infective proteins, are not eliminated using conventional methods. Therefore incineration is recommended.

Answer 367

Larger than 0.3 um ## Footnote Filtration of air is accomplished using high-efficiency particulate air (HEPA) filters designed to remove organisms larger than 0.3 μm from isolation rooms, operating rooms, and biologic safety cabinets (BSCs).

Answer 368

Neisseria gonorrhoeae ## Footnote Credé's prophylaxis: eye drop solution containing 1% silver nitrate is still placed in the eyes of newborns to prevent infections with Neisseria gonorrhoeae.

Answer 369

RACE ## Footnote The important actions in case of fire and the order in which to perform tasks can be remembered with the acronym RACE: 1. Rescue any injured individuals. 2. Activate the fire alarm. 3. Contain (smother) the fire, if feasible (close fire doors). 4. Extinguish the fire, if possible.

Answer 370

Type A fire extinguisher ## Footnote Type A fire extinguishers are used for trash, wood, and paper; type B extinguishers are used for chemical fires; and type C extinguishers are used for electrical fires. Combination type ABC extinguishers are found in most laboratories so that personnel need not worry about which extinguisher to reach for in case of a fire.

Answer 371

Type C fire extinguisher ## Footnote Type A fire extinguishers are used for trash, wood, and paper; type B extinguishers are used for chemical fires; and type C extinguishers are used for electrical fires. Combination type ABC extinguishers are found in most laboratories so that personnel need not worry about which extinguisher to reach for in case of a fire.

Answer 372

Combination ABC ## Footnote Type A fire extinguishers are used for trash, wood, and paper; type B extinguishers are used for chemical fires; and type C extinguishers are used for electrical fires. Combination type ABC extinguishers are found in most laboratories so that personnel need not worry about which extinguisher to reach for in case of a fire.

Answer 373

Laboratory director and supervisor ## Footnote The laboratory director and supervisor is legally responsible for ensuring that an Exposure Control Plan has been implemented and that the mandated safety guidelines are followed. The plan identifies tasks that are hazardous to employees and promotes employee safety

Answer 374

HBV vaccine ## Footnote All employees should also be offered, at no charge, the HBV vaccine and annual skin tests for tuberculosis.

Answer 375

Biological safety cabinet class I ## Footnote Class I cabinets allow room (unsterilized) air to pass into the cabinet and around the area and material within, sterilizing only the air to be exhausted. They have negative pressure, are ventilated to the outside, and are usually operated with an open front.

Answer 376

Biological safety cabinet class IIA ## Footnote A class IIA cabinet is self-contained, and 70% of the air is recirculated.

Answer 377

Biological safety cabinet class IIB ## Footnote The exhaust air in class IIB cabinets is discharged outside the building. A class IIB cabinet is selected if radioisotopes, toxic chemicals, or carcinogens will be used.

Answer 378

Biological safety cabinet class IIB ## Footnote The exhaust air in class IIB cabinets is discharged outside the building. A class IIB cabinet is selected if radioisotopes, toxic chemicals, or carcinogens will be used.

Answer 379

Biological safety cabinet class III ## Footnote Because they are completely enclosed and have negative pressure, class III cabinets afford the most protection to the worker. Air coming into and going out of the cabinet is filter sterilized, and the infectious material within is handled with rubber gloves that are attached and sealed to the cabinet.

Answer 380

Biological safety cabinet class IIA ## Footnote Most hospital clinical microbiology laboratory scientists use class IIA cabinets.

Answer 381

Biosafety level 1 (BSL-1) agents ## Footnote Biosafety Level (BSL-1) agents include those that have no known potential for infecting healthy people and are well defined and characterized. These agents are used in laboratory teaching exercises for undergraduate, secondary educational training and teaching laboratories for students in microbiology. BSL-1 agents include Bacillus subtilis and Naegleria gruberi; in addition, exempt organisms under the NIH guidelines are representative microorganisms in this category.

Answer 382

Biosafety level 2 (BSL-2) agents ## Footnote BSL-2 agents are those most commonly being sought in clinical specimens and used in diagnostic, teaching, and other laboratories. They include all the common agents of infectious disease, as well as HIV, hepatitis B virus, Salmonella organisms, and several more unusual pathogens.

Answer 383

BSL-3 agents ## Footnote BSL-3 procedures have been recommended for the handling of material suspected of harboring organisms unlikely to be encountered in a routine clinical laboratory and for such organisms as Mycobacterium tuberculosis, Coxiella burnetii, the mold stages of systemic fungi, and for some other organisms when grown in quantities greater than that found in patient specimens.

Answer 384

BSL-4 agents ## Footnote BSL-4 agents are exotic agents that are considered high risk and cause life-threatening disease. They include Marburg virus or Congo-Crimean hemorrhagic fever. Most of the facilities that deal with BSL-4 agents are public health or research laboratories. As mentioned, BSL-4 agents pose life-threatening risks and are transmitted via aerosols; in addition, no vaccine or therapy is available for these organisms.

Answer 385

Abscess (also lesion, wound, pustule and ulcer) ## Footnote Table 5-1 of Bailey & Scott's Abscess (also Lesion, Wound, Pustule, Ulcer) Aerobic swab moistened with Stuart’s or Amie’s medium

Answer 386

Sterile saline or 70% alcohol ## Footnote Table 5-1 of Bailey & Scott's Abscess (also Lesion, Wound, Pustule, Ulcer) Wipe area with sterile saline or 70% alcohol

Answer 387

Less than 15 minutes ## Footnote Table 5-1 of Bailey & Scott's

Answer 388

Water ## Footnote Table 5-1 of Bailey & Scott's Sputum: have patient brush teeth and then rinse or gargle with water before collection.

Answer 389

Cary-Blair medium ## Footnote Table 5-1 of Bailey & Scott's

Answer 390

Less than 1 hour at room temperature ## Footnote Table 5-1 of Bailey & Scott's Within 24 hrs/RT Unpreserved <1 hr/RT

Answer 391

Three specimens ## Footnote Table 5-1 of Bailey & Scott's Collect three specimens every other day at a minimum for outpatients; hospitalized patients (inpatients) should have a daily specimen collected for 3 days; specimens from inpatients hospitalized more than 3 days should be discouraged.

Answer 392

Wipe nails or skin with 70% alcohol ## Footnote NOTE: PATIENT PREPARATION: Nails or skin: wipe with 70% alcohol FOR MICROSCOPY/VISUALIZATION OF FUNGAL ELEMENTS: KOH Table 5-1 of Bailey & Scott's Nails or skin: wipe with 70% alcohol Fungal elements, including yeast cells and pseudohyphae, may be visualized with a 10% potassium hydroxide (KOH) preparation, calcofluor white fluorescent stain, or periodic acid-Schiff (PAS) stain.

Answer 393

Neisseria meningitidis ## Footnote Many microorganisms are susceptible to environmental conditions such as the presence of oxygen (anaerobic bacteria), changes in temperature (Neisseria meningitidis), or changes in pH (Shigella). Thus, use of special preservatives or holding media for transportation of specimens delayed for more than 2 hours is important to ensure organism viability (survival).

Answer 394

Shigella sp. ## Footnote Many microorganisms are susceptible to environmental conditions such as the presence of oxygen (anaerobic bacteria), changes in temperature (Neisseria meningitidis), or changes in pH (Shigella). Thus, use of special preservatives or holding media for transportation of specimens delayed for more than 2 hours is important to ensure organism viability (survival)

Answer 395

4C ## Footnote Urine, stool, viral specimens, sputa, swabs, and foreign devices such as catheters should be stored at 4° C. Serum for serologic studies may be frozen for up to 1 week at –20° C, and tissues or specimens for long-term storage should be frozen at –70° C.

Answer 396

Specimen requisition ## Footnote The specimen (or test) requisition is an order form that is sent to the laboratory along with a specimen. Often the requisition is a hard (paper) copy of the physician’s orders and the patient’s demographic information (e.g., name and hospital number). A complete requisition should include the following: * The patient’s name * Hospital number * Age or date of birth * Sex * Collection date and time * Ordering physician * Exact nature and source of the specimen * Diagnosis * Current antimicrobial therapy

Answer 397

All of these ## Footnote REJECTION OF UNACCEPTABLE SPECIMENS Criteria for specimen rejection should be set up and distributed to all clinical practitioners. In general, specimens are unacceptable if any of the following conditions apply: * The information on the label does not match the information on the requisition or the specimen is not labeled at all (patient’s name or source of specimen is different). * The specimen has been transported at the improper temperature. * The specimen has not been transported in the proper medium (e.g., specimens for anaerobic bacteria submitted in aerobic transports). * The quantity of specimen is insufficient for testing (the specimen is considered quantity not sufficient [QNS]). * The specimen is leaking. * The specimen transport time exceeds 2 hours post-collection or the specimen is not preserved. * The specimen was received in a fixative (formalin), which, in essence, kills any microorganism present. * The specimen has been received for anaerobic culture from a site known to have anaerobes as part of the normal flora (vagina, mouth). * The specimen is dried. * Processing the specimen would produce information of questionable medical value (e.g., Foley catheter tip).

Answer 398

All of these ## Footnote Common panic values include the following: * Positive blood cultures * Positive spinal fluid Gram stain or culture * Streptococcus pyogenes (group A Streptococcus) in a surgical wound * Gram stain suggestive of gas gangrene (large box-carshaped gram-positive rods) * Blood smear positive for malaria * Positive cryptococcal antigen test * Positive acid-fast stain * Detection of a select agent (e.g., Brucella) or other significant pathogen (e.g., Legionella, vancomycinresistant S. aureus, or other antibiotic-resistant organisms as outlined by the facility and infection control policies).

Answer 399

Dark purple to a deep blue ## Footnote Gram-positive organisms will appear dark purple to a deep blue.

Answer 400

Pink to a deep magenta ## Footnote Gram-negative organisms will appear pink to a deep magenta.

Answer 401

Acridine orange stain ## Footnote The fluorochrome acridine orange binds to nucleic acid. This staining method can be used to confirm the presence of bacteria in blood cultures when Gram stain results are difficult to interpret or when the presence of bacteria is highly suspected but none are detected using light microscopy. Because acridine orange stains all nucleic acids, it is nonspecific. Therefore, all microorganisms and host cells will stain and give a bright orange fluorescence.

Answer 402

Decolorization using alcohol or acetone ## Footnote MOST CRTITICAL STEP OF GRAM STAINING: DECOLORIZATION STEP The decolorization step distinguishes gram-positive from gram-negative cells. The difference in composition between gram-positive cell walls, which contain thick peptidoglycan with numerous teichoic acid cross-linkages, and gram-negative cell walls, which consist of a thinner layer of peptidoglycan, and the presence of an outer lipid bilayer that is dehydrated during decolorization, accounts for the Gram staining differences between these two major groups of bacteria.

Answer 403

300 OIF ## Footnote Before a smear is reported as negative, it should be examined carefully by scanning at least 300 oil immersion fields (magnification ×1000), equivalent to three full horizontal sweeps of a smear that is 2 cm long and 1 cm wide.

Answer 404

Spirochetes such as Treponema pallidum ## Footnote Dark-field microscopy is used to detect spirochetes, the most notorious of which is the bacterium Treponema pallidum, the causative agent of syphilis. Spirochetes viewed using dark-field microscopy will appear extremely bright against a black field. The use of dark-field microscopy in diagnostic microbiology has decreased with the advent of reliable serologic techniques for the diagnosis of syphilis.

Answer 405

Calcofluor white ## Footnote The cell walls of fungi will bind the stain calcofluor white, which greatly enhances fungal visibility in tissue and other specimens. This fluorochrome is commonly used to directly detect fungi in clinical material and to observe subtle characteristics of fungi grown in culture. Calcofluor white may also be used to visualize some parasites such as microsporidia.

Answer 406

Exotoxin ## Footnote Exotoxins * Most commonly associated with gram-positive bacteria * Produced and released by living bacteria; do not require bacterial death for release * Specific toxins target specific host cells; the type of toxin varies with the bacterial species. * Some kill host cells and help spread bacteria in tissues (e.g., enzymes that destroy key biochemical tissue components or specifically destroy host cell membranes). * Some destroy or interfere with specific intracellular activities (e.g., interruption of protein synthesis, interruption of internal cell signals, or interruption of neuromuscular system).

Answer 407

Endemic ## Footnote Endemic: A disease constantly present at some rate of occurrence in a particular location Epidemic: A larger than normal number of diseased or infected individuals in a particular location Pandemic: An epidemic that spans the world Outbreak: A larger than normal number of diseased or infected individuals that occurs over a relatively short period

Answer 408

Epidemic ## Footnote Endemic: A disease constantly present at some rate of occurrence in a particular location Epidemic: A larger than normal number of diseased or infected individuals in a particular location Pandemic: An epidemic that spans the world Outbreak: A larger than normal number of diseased or infected individuals that occurs over a relatively short period

Answer 409

Pandemic ## Footnote Endemic: A disease constantly present at some rate of occurrence in a particular location Epidemic: A larger than normal number of diseased or infected individuals in a particular location Pandemic: An epidemic that spans the world Outbreak: A larger than normal number of diseased or infected individuals that occurs over a relatively short period

Answer 410

Disease incidence

Answer 411

Disease prevalence

Answer 412

Lungs ## Footnote Normal flora can offer the host protection against infections by providing competition to pathogenic bacteria. The lungs are not typically colonized with bacterial flora. When diagnosing lower respiratory track infections, procedures such as bronchoscopy or percutaneous transtracheal aspirate are used to obtain a specimen that is not contaminated by upper respiratory tract flora.

Answer 413

Lactobacillus ## Footnote The flora of the female genital tract changes with age and the associated effects of pH and estrogen concentration in the mucosa. Lacto- bacillus spp. are the predominant flora during childbearing years. Earlier and later in life, staphylococci and corynebacteria predominate.

Answer 414

Staphylococcus spp. from Micrococcus spp. ## Footnote Staphylococci are susceptible to furazolidone, giving zones of inhibition that are 15 mm or greater. Micrococcus spp. are resistant to furazolidone, giving zones of 6–9 mm. The test is performed as a disk susceptibility procedure using a blood agar plate.

Answer 415

All of these ## Footnote The slide coagulase test using rabbit plasma with EDTA detects bound coagulase or “clumping factor” on the surface of the cell wall, which reacts with the fibrinogen in the plasma. This test is not positive for all strains of S. aureus, and a negative result must be confirmed by the tube method for detecting “free coagulase” or extracellular coagulase. The tube test is usually positive within 4 hours at 35°C; however, a negative result must then be incubated at room temperature for the remainder of 18–24 hours. Some strains produce coagulase slowly or produce fibrinolysin, which dissolves the clot at 35°C. Latex agglutination procedures utilize fibrinogen and IgG-coated latex beads that detect protein A on the staphylococcal cell wall.

Answer 416

Acetoin ## Footnote The production of acetoin by S. aureus from glucose or pyruvate differentiates it from S. intermedius, which is also coagulase positive. This test is also called the VP test. Acetoin production is detected by addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation. A distinct pink color within 10 minutes denotes a positive test.

Answer 417

All of these ## Footnote S. epidermidis represents 50%–80% of all coagulase-negative Staphylococcus spp. recovered from numerous clinical specimens. It is of special concern in nosocomial infections because of its high resistance to antibiotics.

Answer 418

S. epidermidis

Answer 419

Novobiocin susceptibility ## Footnote S. epidermidis and S. saprophyticus are the two possibilities because they are both catalase positive, coagulase negative, urease positive, and ferment lactose. Novobiocin susceptibility is the test of choice for differentiating these two species. S. epidermidis is sensitive but S. saprophyticus is resistant to 5 μg of novobiocin.

Answer 420

Oxacillin ## Footnote Oxacillin is the drug used to screen staphylococci for resistance to antibiotics having the β-lactam ring. Included in this group are penicillin, cephalosporin, monobactam, and carbapenem. MRSA defines strains of staph that are resistant to all of these antibiotic groups. MRSA strains are treated with vancomycin or oxazolidinone.

Answer 421

Anti-streptolysin O

Answer 422

Bacitracin, CAMP, PYR ## Footnote Group B streptococci (S. agalactiae) are important pathogens and can cause serious neonatal infections. Women who are found to be heavily colonized vaginally with S. agalactiae pose a threat to the newborn, especially within the first few days after delivery. The infection acquired by the infant is associated with pneumonia.

Answer 423

Optochin, bile solubility, PYR ## Footnote S. pneumoniae colonies appear as α-hemolytic “donut” shaped colonies on 5% sheep blood agar. The mucoid colonies may appear “wet” or “watery” due to the capsule surrounding the organism. The Gram-stained smear reveals lancet-shaped gram-positive cocci in pairs surrounded by a clear area (the capsule). To differentiate the viridans streptococci from S. pneumoniae, the most appropriate test is the Optochin disk test. S. pneumoniae on blood agar are susceptible to Optochin but viridans streptococci are resistant.

Answer 424

Enterococcus faecalis

Answer 425

S. pneumoniae

Answer 426

Enterococcus faecalis ## Footnote Enterococcus (Streptococcus) faecalis is the cause of up to 20% of the bacterial endocarditis cases and is the most commonly encountered species in this condition.

Answer 427

Staphylococcal cross-streak test ## Footnote The staphylococcal streak, across the NVS inoculum, provides the nutrients needed. Very small colonies of NVS can be seen growing adjacent to the staphylococcal streak on the blood agar plate in a manner similar to the satellite phenomenon of Haemophilus spp. around S. aureus.

Answer 428

Hanging-drop motility (25°C) and catalase ## Footnote L. monocytogenes is catalase positive and displays a “tumbling” motility at room temperature. Streptococcus spp. are catalase negative and nonmotile.

Answer 429

Culture specimens in ambient oxygen at 37C ## Footnote Cultures must be incubated in 3%–7% CO2 at 35°C. Cultures should be held a minimum of 48 hours before being considered negative.

Answer 430

Enterobacteriaceae from gastrointestinal specimens

Answer 431

MacConkey agar with sorbitol

Answer 432

Cefsulodin–Irgasan–Novobiocin (CIN) agar

Answer 433

Citrobacter freundii ## Footnote Biochemical differentiation is essential because Citrobacter isolates may give a falsepositive agglutination test with Salmonella grouping sera. C. freundii strains, like Salmonella spp., are usually H2S producers and may be confused with Salmonella spp. unless the proper biochemical tests are utilized. C. freundii and Salmonella spp. are adonitol, indole, and malonate negative. However, C. freundii is KCN positive, whereas Salmonella spp. are KCN negative.

Answer 434

Campylobacter spp. ## Footnote Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.

Answer 435

Yersinia pestis

Answer 436

Inhalation of contaminated airborne droplets ## Footnote Bubonic plague involves an inflammatory swelling of the lymph nodes of the axilla and groin, whereas pneumonic plague is associated with an airborne route involving the lungs. Both infections are caused by the same member of the Enterobacteriaceae family, Yersinia pestis.

Answer 437

Indole, phenylalanine deaminase, and urease ## Footnote A swarmer on blood agar would most likely be a Proteus spp. A lactose nonfermenter and swarmer that is often isolated from urinary tract infections is P. mirabilis.

Answer 438

Beta-lactamase ## Footnote Antimicrobial resistance in Neisseria gonorrhea is widespread. The production of betalactamase (penicillinase) breaks open the beta-lactam ring of penicillin, destroying its activity. Thus, N. gonorrhoeae that produces beta lactamase are resistant to penicillin.

Answer 439

Chocolate agar plate ## Footnote Enriched media such as chocolate agar has no inhibitory effects on bacterial growth and contains additional nutrients that support the growth of fastidious organisms such as H. influenzae and Neisseria.

Answer 440

Endocervical - chocolate, Martin Lewis ## Footnote Chocolate agar and chocolate agar based selective media (Martin Lewis) are routinely used for the recovery of Neisseria gonorrhoeae from genital specimens. Sputum and urine specimens are routinely processed using a general-purpose media (blood agar) and a selective agar (EMB or MacConkey). In addition, chocolate agar is routinely included to enhance the recovery of fastidious organisms such as H. influenzae. CSF is routinely processed using blood and chocolate agars.

Answer 441

LIM broth ## Footnote Detection of group B streptococcus (GBS) in the genital and gastrointestinal tracts of pregnant women can identify infants at risk for GBS infection. The CDC currently recommends the collection of vaginal and rectal swab or a single swab inserted first into the vagina and then the rectum at 35 to 37 weeks of gestation. The swab(s) should be inoculated into a selective broth medium such as LIM broth (ToddHewitt broth with colistin and nalidixic acid). The use of vaginal rectal swabs and selective broth medium greatly increases the recovery of GBS.

Answer 442

Bile solubility ## Footnote Bile solubility testing of alpha hemolytic streptococci differentiates S. penumoniae (soluble) from other alpha-hemolytic streptococci such as viridans streptococci (insoluble).

Answer 443

Pneumococci ## Footnote Optochin susceptibility is used to differentiate S. pneumoniae, which are susceptible from other alpha hemolytic streptococci which are resistant.

Answer 444

Bile esculin, PYR, bacitracin and hippurate ## Footnote Bile esculin, PYR, bacitracin and hippurate are biochemical test for the presumptive or definitive identification of beta hemolytic streptococci such as S. pyogenes, S. agalactiae and Enterococcus.

Answer 445

Shigella ## Footnote Shigella is lactose negative, most species do not produce gas, are VP, urea, lysine decarboxylase and citrate negative, and they are non motile.

Answer 446

Klebsiella pneumoniae ## Footnote Klebsiella is the only distractor that is VP positive, and the other biochemical reactions are typical for K. pneumoniae.

Answer 447

Salmonella typhimurium ## Footnote Salmonella is the only distractor that produces H2S. Also, Klebsiella and E. coli produce acid/acid reactions in TSI.

Answer 448

Shigella dysenteriae ## Footnote Salmonella produces H2S in TSI and Yersinia produces an acid slant and acid butt. Shigella fits this biochemical profile.

Answer 449

KCN, malonate, beta-galactosidase, lysine decarboxylase ## Footnote Salmonella are positive for lysine decarboxylase and most are negative for KCN, malonate and ONPG. Citrobacter are negative for lysine decarboxylase and positive for growth in KCN.

Answer 450

Yersinia pestis ## Footnote Yersinia pestis is classically described as having a “safety pin” appearance on Wayson’s stain. This patient’s presentation is classic for bubonic plague.

Answer 451

It is oxidase positive ## Footnote Enterobacteriaceae ferments glucose and are oxidase negative. Pleisomonas was a member of the Vibrio family in part because it is oxidase positive. However it was moved to the Enterobacteriaceae despite its positive oxidase reaction.

Answer 452

Will grow on MacConkey and EMB media ## Footnote Both organisms are gram negative, Neisseria gonorrhoeae is fastidious and does not grow on MacConkey or EMB agar, but Acinetobacter does. Neisseria is oxidase positive and Acinetobacter is oxidase negative.

Answer 453

Eikenella corrodens ## Footnote “Pitting of agar” and the bleach smell of the colonies are hallmark characteristics of Eikenella corrodens.

Answer 454

Requirement of 5 to 10% CO2 for growth ## Footnote The HACEK group of organisms are gram negative bacilli that require increased CO2 for growth. They are commonly associated with endocarditis and include Haemophilus species (especially H. aprophilus), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens and Kingella species.

Answer 455

Carbon dioxide ## Footnote Neisseria gonorrhoeae requires an enhanced CO2 atmosphere for optimal growth.

Answer 456

Oxidase positive and glucose positive, maltose negative ## Footnote Neisseria gonorrhoeae is oxidase positive and ferments glucose but not maltose.

Answer 457

Klebsiella oxytoca ## Footnote K. oxytoca is similar to K. pneumoniae except that the indole test is positive for K. oxytoca.

Answer 458

Yersinia enterocolitica ## Footnote Y. enterocolitica has been associated with fatal bacteremia and septic shock from contaminated blood transfusion products. The motility at room temperature is a clue to this identification.

Answer 459

E. coli O157:H7 ## Footnote E. coli O157:H7 is usually the most common isolate from bloody stools of the enterohemorrhagic E. coli (EHEC) group, which results from undercooked beef. These strains are waterborne and foodborne, and the infections from E. coli O157:H7 are greatest during the summer months in temperate climates.

Answer 460

E. coli O157:H7 or Shigella spp. ## Footnote Both E. coli O157:H7 and Shigella spp. are invasive and cause bloody stools.

Answer 461

Indole, phenylalanine deaminase, and urease ## Footnote A swarmer on blood agar would most likely be a Proteus spp. A lactose nonfermenter and swarmer that is often isolated from urinary tract infections is P. mirabilis.

Answer 462

Acinetobacter spp. ## Footnote Acinetobacter spp. are plump coccobacilli that tend to resist alcohol decolorization; they may be mistaken for Neisseria spp.

Answer 463

Requirement of 5 to10% CO2 for growth ## Footnote The HACEK group of organisms are gram negative bacilli that require increased CO2 for growth. They are commonly associated with endocarditis and include Haemophilus species (especially H. aprophilus), Actinobacillus actinomycetemcomitans, Cardiobacterium hominis, Eikenella corrodens and Kingella species

Answer 464

Growth at 42ºC ## Footnote Pseudomonas aeruginosa grows at 42˚C but this temperature is inhibitory for other Pseudomonas species.

Answer 465

Pseudomonas aeruginosa ## Footnote Pseudomonas aeruginosa is a major cause of nosocomial pneumonia in health-care related settings. A major portion of the P. aeruginosa associated nosocomial pneumonia occurs in immunocompromised patients in intensive care units who have undergone intubation (ventilator-associated pneumonia). Among the conditions that predispose immunocompromised patients to P. aeruginosa infection is the utilization of contaminated respiratory equipment during intubation. P. aeruginosa is a gram-negative, oxidase positive, obligate aerobe that produces numerous extracellular virulence factors including exotoxins, proteases, and rhamnolipid.

Answer 466

Pseudomonas aeruginosa ## Footnote P. aeruginosa is often recovered from the respiratory secretions of cystic fibrosis patients. If the patient is chronically infected with the mucoid strain of P. aeruginosa, the biochemical identification is very difficult. The mucoid strain results from production of large amounts of alginate, a polysaccharide that surrounds the cell.

Answer 467

Pseudomonas aeruginosa ## Footnote The oxidase test, as well as growth at 42°C, distinguish P. aeruginosa from the other pseudomonads listed, particularly B. cepacia, which is also associated with cystic fibrosis.

Answer 468

Pseudomonas aeruginosa ## Footnote Cetrimide (acetyl trimethyl ammonium bromide) agar is used for the isolation and identification of P. aeruginosa.

Answer 469

Pseudomonas aeruginosa ## Footnote Swimmer's ear is a form of external otitis common to persons who swim and fail to completely dry their ear canals when they get out of the water. The organism most commonly associated with this condition is Pseudomonas aeruginosa. It is an organism known to be an opportunistic pathogen and one that favors a watery environment.

Answer 470

Stenotrophomonas sp. ## Footnote Stenotrophomonas maltophilia Large, smooth, glistening colonies with uneven edges and lavender-green to light purple pigment; greenish discoloration underneath growth; ammonia smell

Answer 471

Stenotrophomonas maltophilia ## Footnote S. maltophilia is the third most frequently isolated nonfermentative gram-negative rod in the clinical laboratory. Cystic fibrosis patients are at greater risk for infections because of previous antimicrobial treatment and recurrent pneumonia and because some strains may be colonizers.

Answer 472

Synthesis of hemin ## Footnote The porphyrin test is an alternative method for detecting heme- producing species of Haemophilus. It detects whether or not the organism converts the substrate deltaaminolevulinic acid into porphyrins or porphobilinogen which are intermediates for the synthesis of X factor.

Answer 473

H. ducreyi ## Footnote Chancroid is the sexually transmitted disease caused by H. ducreyi. The initial symptom is the development of a painful genital ulcer and inguinal lymphadenopathy. The disease is more prevalent in the tropics than in temperate parts of the world. The bacteria produce buboes in the groin and can cause a septicemia.

Answer 474

Haemophilus influenzae ## Footnote Haemophilus influenzae is a gram-negative bacillus. In young children, it can cause pneumonitis, sinusitis, otitis, and meningitis. Occasionally, it produces a fulminative laryngotracheitis with such severe swelling of the epiglottis that tracheostomy becomes necessary. Clinical infections with this organism after the age of 3 years are less frequent, especially since approval of the type b vaccine.

Answer 475

Type b ## Footnote H. influenzae type b (Hib) is most commonly encountered in serious infections in humans.

Answer 476

Haemophilus influenzae ## Footnote "Satellitism" is the name given to the appearance of colonies of Haemophilus influenzae on sheep blood agar medium around colonies of organisms that provide an essential growth factor. H. influenzae requires both hemin and NAD. Colonies of some organisms, such as Staphylococcus and Neisseria, produce NAD, which diffuses into the surrounding agar and enables H. influenzae to grow.

Answer 477

Aggregatibacter ## Footnote Haemophilus aphrophilus and Haemophilus paraphrophilus have been reclassified as a single species based on multilocus sequence analysis. Aggregatibacter aphrophilus now includes both the hemin-dependent and heminindependent isolates.

Answer 478

Aggregatibacter aphrophilus ## Footnote H. aphrophilus is the only species that does not require X or V factors. H. aphrophilus is an uncommon cause of endocarditis and is the H member of the HACEK group of bacteria associated with slowly progressive (subacute) bacterial endocarditis.

Answer 479

Thiosulfate citrate bile salts sucrose medium ## Footnote V. cholerae as well as other vibrios, including V. parahaemolyticus and V. alginolyticus, are isolated best on thiosulfate citrate bile salts sucrose medium, although media such as mannitol salt agar also support the growth of vibrios. Maximal growth occurs at a pH of 8.5 to 9.5 and at 37°C incubation.

Answer 480

Vibrio cholerae ## Footnote The toxin of V. cholerae and LT enterotoxin from E. coli are similar. Cyclic AMP is increased, as is fluid and electrolyte release from the crypt cells into the lumen of the bowel. Watery, profuse diarrhea ensues.

Answer 481

Campylobacter jejuni ## Footnote Most Campylobacter species grow best under lower oxygen tension in an atmosphere of 5% oxygen, 10% carbon dioxide and 85% nitrogen. E. coli and Proteus mirabilis are facultative anaerobes and Pseudomonas is an aerobe.

Answer 482

Skirrow medium ## Footnote Skirrow medium is an enriched selective blood agar medium used for the isolation of Campylobacter from specimens with mixed flora.

Answer 483

42C ## Footnote Campylobacter jejuni/coli grow better at 42˚C than 37˚C and other organisms in the colon are inhibited at this high temperature.

Answer 484

Subculture the bottle, and incubate in microaerophilic conditions

Answer 485

Guillain-Barré syndrome ## Footnote Most recently, postinfectious complications with C. jejuni have been recognized and include reactive arthritis and Guillain-Barré syndrome, an acute demyelination (removal of the myelin sheath from a nerve) of the peripheral nerves.

Answer 486

Campylobacter jejuni

Answer 487

Helicobacter pylori ## Footnote Helicobacter pylori was first recognized as a possible cause of gastritis and peptic ulcer. This organism is readily isolated from gastric biopsies but not from stomach contents. It is similar to Campylobacter species and grows on chocolate agar at 37°C in the same microaerophilic environment suitable for C. jejuni (Campy-Pak or anaerobic jar [Gas Pak] without the catalyst). H. pylori, however, grows more slowly than C. jejuni, requiring 5 to 7 days incubation. C. jejuni grows optimally at 42°C, not 37°C, as does H. pylori.

Answer 488

Urea broth ## Footnote Helicobacter pylori produce large amounts of extracellular urease and are positive for urea within 2 hours.

Answer 489

Bordetella pertussis ## Footnote B. pertussis, the primary pathogen of whooping cough, uses several mechanisms to overcome the immune defenses of healthy individuals.

Answer 490

Nasopharyngeal swab ## Footnote Posterior nasopharyngeal cultures are recommended for the recovery of Bordetella pertussis in suspected cases of pertussis (whooping cough). Swabs of the nasopharynx are inoculated on the selective agar Regan-Lowe. Cephalexin is added to the culture medium to inhibit the growth of contaminating indigenous flora.

Answer 491

Regan-Lowe agar ## Footnote Regan-Lowe agar is an enriched and selective medium for the isolation of Bordetella pertussis. Cephalexin is added to inhibit nasopharyngeal flora. It provides better isolation of Bordetella pertussis than Bordet-Gengou medium.

Answer 492

Bordetella pertussis ## Footnote Bordetella pertussis is the etiologic agent of pertussis, or whooping cough. On BordetGengou or Regan-Lowe agars, the organism forms small, round colonies that resemble mercury droplets. A nasopharyngeal swab is recommended as the optimal specimen for the recovery of this agent.

Answer 493

Rapid hydrolysis of urea ## Footnote Both organisms are oxidase positive; Bordetella bronchiseptica is urea positive within 4 hours.

Answer 494

Brucella melitensis ## Footnote Brucella are small, aerobic, Gram-negative coccobacilli. Of the four well-characterized species of Brucella, only one—B. melitensis—characteristically infects both goats and humans. Brucellosis may be associated with gastrointestinal and neurologic symptoms, lymphadenopathy, splenomegaly, hepatitis, and osteomyelitis.

Answer 495

Brucellosis ## Footnote Brucella infects cattle and may be transmitted to humans by the ingestion of contaminated milk or other dairy products. Milk is able to support the growth of many clinically significant microorganisms, which may often be ingested in unpasteurized dairy products.

Answer 496

Charcoal and yeast extract ## Footnote Buffered Charcoal yeast extract medium is as specialized enrichment medium for the isolation of Legionella. The nutritive base includes yeast extract. Charcoal is added to the medium as detoxifying agent.

Answer 497

Bronchial washings ## Footnote Tissue samples from the lower respiratory tract (lung biopsy) have the greatest yield of positive cultures for Legionella pneumophila. However, these specimens require invasive procedures and are not commonly performed. Cultures of lower respiratory tract specimens, such as bronchial wash and expectorated sputum, are appropriate for the isolation of L. pneumophila.

Answer 498

Cystine glucose blood agar ## Footnote Francisella tularensis is fastidious and not readily recovered in culture. Cysteine blood glucose agar is an enriched medium with beef heart infusion, peptones, glucose and rabbit blood. It also includes cystine, which is required by F. tularensis for growth.

Answer 499

Francisella tularensis ## Footnote Francisella tularensis requires cysteine or cystine for growth. Glucose-cysteine with thiamine and cystine heart media are commercially available for suspected cases of tularemia.

Answer 500

Pasteurella multocida ## Footnote Pasteurella (gram-negative coccobacilli) are primarily animal pathogens, but they can cause a wide range of human diseases. Pasteurella multocida occurs worldwide in domestic and wild animals. It is the most common organism in human wounds inflicted by bites of cats and dogs. It is a common cause of hemorrhagic septicemia in a variety of animals. Wounds commonly present with an acute onset (within hours) of redness, swelling, and pain.

Answer 501

Liver cirrhosis ## Footnote P. multocida subsp. multocida is most commonly encountered in clinical specimens. Reported virulence factors for this subspecies include lipopolysaccharide, cytotoxin, six serotypes of the antiphagocytic capsule, surface adhesins, and iron-acquisition proteins. Other manifestations of infection by P. multocida subsp. multocida can include respiratory disease and systemic disease such as endocarditis and septicemia. Liver cirrhosis is viewed as a risk factor for systemic disease.

Answer 502

Gardnerella vaginalis ## Footnote Clue cells: epithelial cells with Gardnerella bacteria attached

Answer 503

Haverhill fever ## Footnote Streptobacillus moniliformis is a gram-negative bacillus that requires media containing blood, serum, or ascites fluid as well as incubation under carbon dioxide (CO2) for isolation from clinical specimens. This organism causes rat-bite fever and Haverhill fever in humans. When S. moniliformis is acquired by ingestion, the disease is called Haverhill fever.

Answer 504

Cystine ## Footnote Streptobacillus moniliformis is a gram-negative bacillus that requires media containing blood, serum, or ascites fluid as well as incubation under carbon dioxide (CO2) for isolation from clinical specimens. This organism causes rat-bite fever and Haverhill fever in humans.

Answer 505

Chromobacterium violaceum ## Footnote Chromobacterium violaceum is a motile, gram-negative bacillus found in soil and water that can be pathogenic for humans. The production of a non-water-soluble violet pigment by these organisms aids in their identification

Answer 506

Chryseobacterium ## Footnote Chryseobacterium spp. are ubiquitous in the environment and are especially associated with moist soil and water. Chryseobacterium (formerly Flavobacterium) meningosepticum, a known nosocomial pathogen, has been implicated in outbreaks of meningitis in hospitals and is associated with the use of contaminated respiratory therapy equipment.

Answer 507

Capnocytophaga ## Footnote Capnocytophaga spp. are fermentative gram-negative bacteria that inhabit the oral cavity of humans. These organisms have been identified as a cause of disease in the oral cavity, and in compromised hosts they have been implicated in systemic disease isolated from cerebrospinal fluid, pleural fluid, and pulmonary secretions. The gliding motility is best observed during the log phase of growth and can be demonstrated by darkfield microscopy and on sheep blood agar by the production of concentrically spreading growth around primary colonies.

Answer 508

Bacillus anthracis ## Footnote Bacillus anthracis are large rectangular gram positive bacilli that produces colonies with an irregular edge (often described as Medusa-head appearance) on blood agar. Colonies are non hemolytic, catalase positive and non motile.

Answer 509

Nonhemolytic and nonmotile ## Footnote B. ANTHRACIS: NONMOTILE AND NONHEMOLYTIC B. CEREUS: MOTILE AND BETA-HEMOLYTIC

Answer 510

Woolsorters’ disease ## Footnote Bacillus anthracis Causative agent of anthrax, of which there are three forms: 1. Cutaneous anthrax occurs at site of spore penetration 2 to 5 days after exposure and is manifested by progressive stages from an erythematous papule to ulceration and finally to formation of a black scar (i.e., eschar); may progress to toxemia and death 2. Pulmonary anthrax, also known as woolsorters’ disease, follows inhalation of spores and progresses from malaise with mild fever and nonproductive cough to respiratory distress, massive chest edema, cyanosis, and death 3. Gastrointestinal anthrax may follow ingestion of spores and affects either the oropharyngeal or the abdominal area; most patients die from toxemia and overwhelming sepsis

Answer 511

Bacillus anthracis ## Footnote Bacillus anthracis infects humans by three routes: respiratory, gastrointestinal, and cutaneous. Malignant pustule is the name given to lesions seen in cutaneous anthrax in humans.

Answer 512

Food poisoning ## Footnote Bacillus cereus is of particular interest as an etiologic agent of human cases of food poisoning. This enterotoxin-producing microorganism is most commonly associated with cases of food poisoning following ingestion of reheated rice served at Asian restaurants.

Answer 513

Clostridium and Bacteroides spp. ## Footnote ETHANOL SHOCK SPORE ISOLATION Clostridium species can be recovered from mixed populations of organisms and identified using the ethanol shock spore technique. Ethanol treatment of samples should result in the killing of all vegetative microorganisms. However, clostridial endospores may be resistant to ethanol, and after ethyl alcohol treatment, the spores will germinate upon inoculation and proper incubation on anaerobic blood agar in anaerobic conditions.

Answer 514

Clostridium tetani ## Footnote Corynebacterium species and Propionibacterium species do not produce spores and Bacillus is an aerobic organism.

Answer 515

Clostridium perfringens ## Footnote The reverse CAMP test, production of lecithinase and demonstration of double zone of hemolysis are tests and characteristics used for the identification of Clostridium perfringens.

Answer 516

C. perfringens ## Footnote Clostridium perfringens is the species most commonly associated with clostridial myonecrosis or gas gangrene. These soil and water saprophytes most frequently gain entrance to the human body through traumatic wounds.

Answer 517

Ingestion of a neurotoxin ## Footnote Clostridium botulinum growing in food produces a potent neurotoxin that causes diplopia, dysphagia, respiratory paralysis, and speech difficulties when ingested by humans. The toxin is thought to act by blocking the action of acetylcholine at neuromuscular junctions. Botulism is associated with high mortality; fortunately, C. botulinum infection in humans is rare.

Answer 518

Botulinum toxin ## Footnote Botulinal toxin is the most potent exotoxin known. When absorbed, this exotoxin produces the paralyzing disease botulism. Toxin acts in the body by blocking the release of acetylcholine in the neuromuscular junction of the peripheral nervous system, causing muscle paralysis.

Answer 519

Clostridium difficile ## Footnote Patients treated with antibiotics develop diarrhea that, in most cases, is self-limiting. However, in some instances, particularly in those patients treated with ampicillin or clindamycin, a severe, life-threatening pseudomembranous enterocolitis develops. This disease has characteristic histopathology, and membranous plaques can be seen in the colon by endoscopy. Pseudomembranous enterocolitis and antibiotic-associated diarrhea are caused by an anaerobic Gram-positive rod, Clostridium difficile.

Answer 520

Assays to detect toxin in stool ## Footnote The most rapid and accurate diagnostic method is detecting toxins A and/or B in stool specimens. Cycloserine-cefoxitin-fructose agar (CCFA) is the recommended selective medium for C. difficile, although few laboratories attempt isolation.

Answer 521

Clostridium difficile ## Footnote CCFA is used for recovery of C. difficile from stool cultures. Cycloserine and cefoxitin inhibit growth of gram-negative coliforms in the stool specimen. C. difficile ferments fructose, forming acid that, in the presence of neutral red, causes the colonies to become yellow.

Answer 522

Corynebacterium diphtheriae ## Footnote C. diphtheriae must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area. A flexible calcium alginate nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.

Answer 523

Potassium tellurite ## Footnote Media containing potassium tellurite is used for the recovery of Corynebacterium diphtheriae.

Answer 524

A positive toxigenicity test ## Footnote In order to determine if an isolate of Corynebacterium diphtheriae produces toxin, testing for the presence of diphtheria toxin must be performed using methods such as Elek test or PCR.

Answer 525

L. monocytogenes ## Footnote L. monocytogenes can be presumptively identified by observation of motility by direct wet mount. The organism exhibits characteristic end-over-end tumbling motility when incubated in nutrient broth at room temperature for 1 to 2 hours. Alternatively, characteristic motility can be seen by an umbrella-shaped pattern that develops after overnight incubation at room temperature of a culture stabbed into a tube of semisolid agar.

Answer 526

Listeria monocytogenes ## Footnote Listeria multiplies both extra-cellularly and intracellularly, but under most circumstances, a competent immune system eliminates Listeria. As expected, listeriosis is seen in the very young and the very old, and in people with compromised immune systems. Reports of Listeria food outbreaks have implicated such foods as coleslaw and milk products, especially if not pasteurized. Early-onset-syndrome listeriosis is the result of infection in utero and characterized by sepsis and lesions in multiple organs.

Answer 527

Feta cheese ## Footnote The general population should always properly wash raw vegetables and thoroughly cook vegetables and meat to prevent listerosis. Patients who are immunocompromised and pregnant women should avoid eating soft cheeses (e.g., Mexican-style cheese, feta, brie, Camembert, and blue-veined cheese) to prevent food-borne listeriosis. Additionally, leftover or ready-to-eat foods such as hot dogs or cold cuts should be thoroughly heated before consumption and stored for only a short period before disposal, because L. monocytogenes is able to replicate during refrigeration at 4°C.

Answer 528

Erysipelothrix sp. ## Footnote Erysipelothrix sp. is the only catalase-negative, gram-positive non-spore-forming rod that produces hydrogen sulfide (H2S) when inoculated into triple sugar iron (TSI) agar.

Answer 529

Lipids ## Footnote Mycobacteria characteristically possess a high lipid content, unlike gram-positive cocci and gram-negative bacteria. The high lipid content acts to protect these organisms from dehydration and the lethal effects of alkali, various germicides, alcohol, and acids. Thus, these bacteria do not stain well with the Gram stain, and an acid-fast staining technique must be used.

Answer 530

N-glycolylmuramic acid and an increase in lipid content ## Footnote Mycobacterium spp. have an unusual cell wall structure. The cell wall contains Nglycolylmuramic acid instead of N-acetylmuramic acid, and it has a very high lipid content, which creates a hydrophobic permeability barrier.

Answer 531

PPD test ## Footnote A positive tuberculin skin test reaction is an example of a hypersensitivity reaction. Tuberculin preparations are prepared from culture filtrates, which are precipitated with trichloroacetic acid and are known as purified protein derivative (PPD). A positive test demonstrates an area of induration following an intradermal injection of PPD.

Answer 532

Sputum ## Footnote The mycobacteria are only slightly more resistant to the decontamination procedures than other bacteria. Therefore, it is only appropriate to decontaminate specimens for mycobacteria that are contaminated with normal flora. Because sputum passes through the oral cavity, it contains a large amount of normal oral flora.

Answer 533

Lowenstein-Jensen medium ## Footnote Löwenstein-Jensen (L-J) medium Commonly used medium; good recovery of M. tuberculosis but poor recovery of many other species; M. genovense fails to grow

Answer 534

Chocolate agar ## Footnote Lowenstein-Jensen, Lowenstein-Jensen-Gruft, and Middlebrook media are commonly used for the isolation of the mycobacteria. Chocolate agar will support the growth of Mycobacterium haemophilium; however, chocolate agar is not routinely used for cultures of mycobacteria.

Answer 535

Mycobacterium tuberculosis ## Footnote A serpentine pattern of growth indicates production of cording factor, a virulence factor for M. tuberculosis. M. tuberculosis is positive for niacin accumulation, while the other three species are niacin negative.

Answer 536

M. tuberculosis ## Footnote The human tubercle bacillus is Mycobacterium tuberculosis. Growth of this well-known human pathogen appears in 2 to 3 weeks when incubated at 35°C. These niacin-positive mycobacteria form dry heaping colonies that are buff colored.

Answer 537

Niacin and nitrate reduction tests ## Footnote M. tuberculosis: Positive for niacin and nitrate reduction M. bovis: Negative for niacin and nitrate reduction

Answer 538

Kinyoun stain ## Footnote Acid-fast bacilli can be demonstrated in stained smears of clinical material using the Ziehl-Neelsen or Kinyoun acid-fast stains. The Kinyoun carbol-fuchsin method uses a higher concentration of phenol in the primary stain to accelerate the staining process. Therefore, unlike the Ziehl-Neelsen stain, the Kinyoun stain does not need to be heated.

Answer 539

300 oil immersion fields ## Footnote Before an acid-fast smear is reported as negative, it should be examined carefully by scanning at least 300 oil immersion fields (magnification ×1000), equivalent to three full horizontal sweeps of a smear that is 2 cm long and 1 cm wide.

Answer 540

Bright red rods against a blue background ## Footnote The carbolfuchsin (fuchsin with phenol) stains the mycobacteria red and does not decolorize after the acid–alcohol is added. The background and any other bacterial elements will decolorize and are counterstained blue by the methylene blue.

Answer 541

Auramine-rhodamine ## Footnote Auramine-rhodamine is a fluorescent stain used to visualize the mycobacteria. The bacteria retain the stain and will appear bright yellow against a black background. Because it is easier to see the bacilli, this stain is more sensitive than a fuschin-based stain (e.g., Ziehl-Neelsen).

Answer 542

Kanamycin ## Footnote Rapid development of drug resistance is a concern in the treatment of tuberculosis. Patients are treated generally with a combination of at least two of the primary drugs, such as isoniazid, rifampin, ethambutol, and pyrazinamide. Because of the slowly growing nature of the bacteria, they are innately resistant to a number of agents.

Answer 543

Mycobacterium leprae ## Footnote Hansen disease (leprosy) is caused by Mycobacterium leprae. Cultures of this agent on artificial media, unlike other mycobacteria, have not been successful. Cultivation can be accomplished by injecting bacilli into the foot pads of mice or systemically into armadillos.

Answer 544

M. gordonae ## Footnote Mycobacterium gordonae has been recovered from water stills, faucets, and bodies of water in nature, which is why it has been called the "tap water scotochromogen." These organisms are not considered to be pathogenic for humans, but because they may be recovered as contaminants, their identification is recommended.

Answer 545

M. marinum ## Footnote Mycobacterium marinum is the causative agent of "swimming pool granuloma.

Answer 546

Mycobacterium avium complex ## Footnote Immunocompromised patients, particularly those infected with HIV, can have disseminated mycobacterial infection; most of these infections are caused by M. avium complex.

Answer 547

Mycobacterium scrofulaceum ## Footnote Mycobacterium scrofulaceum is defined as a scotochromogen because of its characteristic of producing pigmentation in the dark. This slowly growing Mycobacterium is a cause of cervical adenitis and other types of infections predominantly in children. Therapy may require susceptibility studies that include the secondary drugs, because the organism is known in some cases to be resistant to isoniazid and streptomycin.

Answer 548

M. chelonei ## Footnote The MacConkey agar used for mycobacteria identification is a different formulation than that used for enterics, in that crystal violet is omitted. A MacConkey agar plate is inoculated with a 7-day broth culture of the test organism. The inoculated plate is then incubated at 37°C. Plates are checked for growth at 5 days, and if no growth is detected, they are checked daily until day 11, at which time they are discarded as negative. M. fortuitum and M. chelonei are the only mycobacteria able to grow on MacConkey agar in 5 days.

Answer 549

M. paratuberculosis ## Footnote M. paratuberculosis is known to cause an ulcerative intestinal disease with chronic diarrhea in cattle known as Johne’s disease. While M. paratuberculosis has been isolated from the intestines of humans with Crohn’s disease, the organism has not yet been proven to cause ileitis in humans.

Answer 550

M. bovis ## Footnote The T2H test differentiates M. tuberculosis from M. bovis. M. tuberculosis is not inhibited by T2H.

Answer 551

M. bovis ## Footnote Mycobacterium bovis is susceptible to 5 ug/mL of thiophene-2-carboxylic acid hydrazide (T2H). This Mycobacterium is associated with cattle and is rarely isolated from humans in the U.S. Growth occurs only at 35°C and is differentiated from other mycobacteria by its susceptibility to T2H.

Answer 552

Nocardia spp. ## Footnote Nocardia spp. should be suspected if colonies that are partially acid fast by the traditional method are positive with the modified acid-fast method using Kinyoun stain and 1% sulfuric acid as the decolorizing agent.

Answer 553

All of the above ## Footnote If the modified acid-fast stain results are positive, the isolate is a probable partially acidfast aerobic actinomycete (i.e., Nocardia, Rhodococcus, Tsukamurella, or Gordonia sp

Answer 554

Mycetoma ## Footnote Infection caused by the non–acid-fast aerobic actinomycetes is usually associated with chronic, granulomatous lesions of the skin referred to as mycetomas. Mycetoma is an infection of subcutaneous tissues that results in tissue swelling and drainage of the sinus tracts.

Answer 555

N. asteroides ## Footnote Infections caused by Nocardia spp. can occur in immunocompetent and immunocompromised individuals. N. asteroides, N. brasiliensis, and N. otitidiscaviarum are the major causes of these infections, with N. asteroides causing greater than 80% of infections.

Answer 556

Actinomyces spp. ## Footnote Direct examination and the macroscopic presence in purulent exudate of “sulfur granules,” which reveal gram-positive filaments when crushed, is diagnostic for an infection with Actinomyces spp.

Answer 557

Actinomyces israelii ## Footnote LOCK JAW: C. tetani LUMPY JAW: Actinomyces

Answer 558

Sodoku ## Footnote Spirillum minus also causes rat-bite fever in humans and is referred to as sodoku. The clinical signs and symptoms are similar to those caused by Streptobacillus moniliformis, except that arthritis is rarely seen in patients with sodoku and swollen lymph nodes are prominent; febrile episodes are also more predictable in sodoku.

Answer 559

Serological analysis ## Footnote Serological tests of the patient’s serum for evidence of syphilis are routinely performed, but culturing is not because research animals must be used for inoculation of the suspected spirochete. T. pallidum does not stain by either the Gram or acid-fast technique.

Answer 560

Syphilis ## Footnote Cardiolipin is a tissue lipid produced as a byproduct of treponemal infection. Nontreponemal tests for syphilis take advantage of antibodies made to cardiolipin. The most commonly used tests are the rapid plasma reagin (RPR) for serum and the Venereal Disease Research Laboratory (VDRL) for cerebrospinal fluid.

Answer 561

Culturing of blood ## Footnote Leptospira spp. are most reliably detected during the first week of illness by the direct culturing of a blood sample. The media of choice are Fletcher semisolid and Stuart liquid medium, both of which are supplemented with rabbit serum.

Answer 562

Lice ## Footnote The human body louse, Pediculus humanus, is the vector for Borrelia recurrentis. Pathogenic species not only have specific vectors but also well-defined geographical distributions.

Answer 563

Lyme disease ## Footnote Lyme disease was first described in 1975 following an outbreak in Lyme, Connecticut. The etiologic agent, Borrelia burgdorferi, is transmitted to humans by the tick vector Ixodes dammini. Clinically the disease peaks in the summer and produces an epidemic inflammatory condition characterized by skin lesions, erythema, headache, myalgia, malaise, and lymphadenitis.

Answer 564

Borrelia spp. ## Footnote Borrelia spp. are often seen on Wright’s-stained smears of peripheral blood as helical bacteria with 3–10 loose coils. They are gram negative but stain well with Giemsa’s stain.

Answer 565

Inclusion conjunctivitis ## Footnote Chlamydia trachomatis is the causative agent of inclusion conjunctivitis, trachoma, and genital tract infections, including lymphogranuloma venereum.

Answer 566

Chlamydia trachomatis ## Footnote Chlamydia trachomatis, a leading cause of blindness, can be detected in corneal scrapings of suspected cases of trachoma and inclusion conjunctivitis.

Answer 567

L1 ## Footnote C. trachomatis serovars L1, L2, L2b, and L3 are invasive causing LGV, in contrast to C. trachomatis serovars A-K, leaving the mucosa to spread to the regional lymph nodes.

Answer 568

Chlamydia psittaci ## Footnote C. psittaci is an endemic pathogen of all bird species. Psittacine birds (e.g., parrots, parakeets) are a major reservoir for human disease, but outbreaks have occurred among turkey-processing workers and pigeon aficionados. The birds may show diarrheal illness or may be asymptomatic. Humans acquire the disease by inhalation of aerosols.

Answer 569

Avians ## Footnote Human infections with Chlamydiophila psittaci (psittacosis) occur after exposure to infected birds and their droppings. A true zoonosis, psittacosis is a disease of birds that may be contracted by humans.

Answer 570

Mycoplasma pneumoniae ## Footnote Mycoplasma pneumoniae causes primary atypical pneumonia. The pneumonia is atypical in that it is milder than the pneumonia caused by Streptococcus pneumoniae.

Answer 571

SP4 agar ## Footnote Provided that arginine is added for Mycoplasma hominis, SP4 agar or broth can be used for the growth of M. pneumoniae and M. hominis.

Answer 572

Mycoplasma hominis ## Footnote When grown on culture media, colonies, most notably M. hominis, are said to have a "fried egg" appearance because the central portion of the colony has grown into the agar and thus appears more dense and is slightly raised.

Answer 573

Mycoplasma pneumoniae ## Footnote Mycoplasma hominis, M. genitalium, and Ureaplasma urealyticum have been linked to human genital infections. These species can also be isolated from asymptomatic sexually active adults. M. pneumoniae is primarily a respiratory tract pathogen.

Answer 574

Fever, headache, and rash ## Footnote Rickettsias are suspected when the triad of fever, headache, and rash is the primary clinical manifestation in patients with an exposure to insect vectors. Infections caused by these organisms may be severe and are sometimes fatal.

Answer 575

Rickettsia rickettsii ## Footnote R. rickettsii Rocky Mountain spotted fever Vector: ticks (Dermacentor spp.)

Answer 576

Chiggers ## Footnote O. tsutsugamushi Scrub typhus Vector: chiggers

Answer 577

Brill-Zinsser disease ## Footnote Humans who have had the classic form of typhus may remain infected with the causative agent Rickettsia prowazekii. Relapses or recrudescence of disease may occur in these persons years or decades after the initial attack. The latent form of infection is known as Brill-Zinsser disease and may serve as an interepidemic reservoir for epidemic typhus.

Answer 578

Rickettsia typhi ## Footnote Murine typhus is transmitted to humans by fleas infected with Rickettsia typhi. Prevalent in the southern U.S., it is primarily a disease of rodents and is sometimes transmitted to humans. Control of disease outbreaks is related to rodent (rat) control and the related rat flea population.

Answer 579

Gimenez stain ## Footnote Direct microscopic examination for Rickettsia organisms is possible using such stains as Giemsa, Machiavello, or Gimenez. The recommended procedure is the nonspecific Gimenez stain, which colors the organisms a brilliant red against a green background.

Answer 580

Trench fever ## Footnote ROCHALIMEA/BARTONELLA QUINTANA: TRENCH FEVER Trench fever, caused by B. quintana, was largely considered a disease of the past. Clinical manifestations of trench fever range from a mild influenza-like headache and bone pain to splenomegaly (enlarged spleen) and a short-lived maculopapular rash.

Answer 581

Stenotrophomonas maltophilia ## Footnote S. maltophilia is the third most frequently isolated nonfermentative gram-negative rod in the clinical laboratory. Cystic fibrosis patients are at greater risk for infections because of previous antimicrobial treatment and recurrent pneumonia and because some strains may be colonizers.

Answer 582

Eikenella corrodens ## Footnote E. corrodens is part of the normal flora of the human mouth and typically “pits” the agar. This organism is capnophilic (needing increased CO2).

Answer 583

Capnocytophaga canimorsus ## Footnote C. canimorsus is associated with septicemia or meningitis following dog bites. All Capnocytophaga strains are capnophilic, facultative anaerobic, gram-negative slender or filamentous rods with tapered ends.

Answer 584

Gardnerella vaginalis ## Footnote G. vaginalis, a gram-negative or gram-variable pleomorphic coccobacillus, causes bacterial vaginosis, but is also present as part of the normal vaginal flora of women of reproductive age with a normal vaginal examination. “Clue cells” are vaginal epithelial cells with gram-negative or gram-variable coccobacilli attached to them.

Answer 585

Hanging-drop motility (25°C) and catalase ## Footnote L. monocytogenes is catalase positive and displays a “tumbling” motility at room temperature. Streptococcus spp. are catalase negative and nonmotile.

Answer 586

H. haemolyticus ## Footnote H. haemolyticus requires both X and V factors for growth and lyses horse erythrocytes.

Answer 587

Clostridium perfringens ## Footnote C. perfringens is an anaerobic gram-positive rod that is often isolated from the tissue of patients with gas gangrene (myonecrosis). Spore production is not usually seen with this organism, which may also stain gram negative.

Answer 588

Legionella pneumophila ## Footnote L. pneumophila is the cause of pneumonia and can occur as part of an epidemic sporadically or nosocomially, or may be community acquired. The appearance of mottled, cut-glass colonies on buffered CYE agar under low power and the use of a direct immunofluorescence technique on sputum samples determine the presence of L. pneumophila. The most common environmental sites for recovery are shower heads, faucets, water tanks, and air-conditioning systems.

Answer 589

Bacteroides fragilis group ## Footnote B. fragilis is the most often isolated gram-negative anaerobic bacillus. It is resistant to many antibiotics. A good screening agar is a 20% bile plate that does not support the growth of Prevotella spp. or Porphyromonas spp.

Answer 590

Chryseobacterium meningosepticum ## Footnote C. meningosepticum is a well-known cause of neonatal meningitis. It will grow well on chocolate agar, producing yellow pigmented colonies.

Answer 591

Swab ## Footnote Specimens for fungal culture must be kept in a moist, sterile environment. Swabs that are dried out or submitted with insufficient material on them should be rejected.

Answer 592

30°C; 21 days

Answer 593

Skin ## Footnote A solution of 10% KOH is used for contaminated specimens such as skin, nail scrapings, hair, and sputum to clear away background debris that may resemble fungal elements.

Answer 594

Zygomycetes ## Footnote Zygomycetes commonly recovered from clinical specimens are Rhizopus spp. and Mucor spp. Both display ASEPTATE HYPHAE, while the other groups above display septate hyphae.

Answer 595

Malassezia furfur

Answer 596

All of the above

Answer 597

M. audouinii, M. canis ## Footnote M. audouinii: fluoresce yellow-green under a Wood’s lamp, no growth in rice medium M. canis :bright yellow-green under a Wood’s lamp, growth in rice medium

Answer 598

In vitro hair perforation ## Footnote T. mentagrophytes: positive hair baiting and urease test T. rubrum: negative hair baiting and urease test

Answer 599

Chromoblastomycosis

Answer 600

Cladosporium spp ## Footnote CHROMOBLASTOMYCOSIS: Cladosporium, Phialophora, and Fonsecaea spp.

Answer 601

Fusarium spp

Answer 602

Fusarium spp.

Answer 603

Aspergillus niger

Answer 604

Yeast phase

Answer 605

Sporothrix schenckii ## Footnote Humans acquire the infection (sporotrichosis) through trauma (thorns, splinters), usually to the hand, arm, or leg. The infection is an occupational hazard for farmers, nursery workers, gardeners, florists, and miners; it is commonly known as “ROSE GARDENER’S DISEASE.”

Answer 606

Histoplasma capsulatum ## Footnote Numerous cases of histoplasmosis have been reported in people who clean out an old chicken coop or barn that has been undisturbed for long periods and in individuals who work in or clean areas that have served as roosting places for starlings and similar birds. SPELUNKERS (i.e., cave explorers) are commonly exposed to the organism when it is aerosolized from bat guano in caves.

Answer 607

Sporothrix schenckii

Answer 608

Paracoccidioides brasiliensis ## Footnote P. brasiliensis yeast forms are sometimes seen as a “MARINER’S WHEEL” because multiple budding cells completely surround the periphery of the parent cell.

Answer 609

Histoplasma capsulatum

Answer 610

Sepedonium spp. ## Footnote Sepedonium spp. are saprophytic molds that do not have a yeast phase and produce large spherical TUBERCULATE MACROCONIDIA like H. capsulatum.

Answer 611

Coccidioides immitis

Answer 612

Coccidioides immitis

Answer 613

Germ tube test

Answer 614

C. albicans, C. dubliniensis ## Footnote The germ tube test is the most generally accepted and economical method used in the clinical laboratory to identify yeasts. Approximately 80% of the yeasts recovered from clinical specimens are C. albicans, and the germ tube test usually provides sufficient identification of the organism within 3 hours. Another Candida species, C. dubliniensis, has been shown to also produce germ tubes. Although C. dubliniensis is infrequently encountered in clinical specimens, supplemental biochemical or morphologic testing may be needed to differentiate it from C. albicans. C. tropicalis produces what have been called “pseudo–germ tubes,” which are constricted at the base or point of germ tube origin on the yeast cell.

Answer 615

C. albicans ## Footnote C. albicans may be identified by the production of GERM TUBES or CHLAMYDOCONIDIA

Answer 616

Acridine orange ## Footnote Acridine orange (AO) staining proved particularly helpful in the early detection of candidemia—one third of all microorganisms missed by Gram stain of instrument-positive bottles were yeasts detected by AO staining.

Answer 617

Cryptococcus neoformans

Answer 618

Phenol oxidase ## Footnote Most isolates of C. neoformans produce phenol oxidase when grown on birdseed medium, producing BROWN TO BLACK PIGMENTED COLONIES.

Answer 619

All of the above ## Footnote Pathogenic fungi, such as C. neoformans complex, Candida krusei and other Candida spp., Trichosporon spp., P. boydii, and Aspergillus spp., are partially or completely inhibited by cycloheximide.

Answer 620

Pneumocystis jiroveci (carinii) ## Footnote Pneumocystis jiroveci (carinii), most recently classified as a fungus but formerly as a parasite, is best recovered by bronchoalveolar lavage or induced sputum in immunocompromised patients. Open lung biopsy sample was the specimen of choice before the AIDS epidemic. Gomori methenamine silver stain is used to identify the organism; it stains the cyst form but not the trophozoites.

Answer 621

Bronchoalveolar lavage fluid ## Footnote Respiratory specimens from the deep portions of the lung, such as bronchoalveolar lavage fluid (BALF), are best for detection of P. jiroveci.

Answer 622

Mitosis ## Footnote STEPS IN VIRAL REPLICATION 1. Attachment (adsorption) 2. Penetration 3. Uncoating 4. Macromolecular synthesis 5. Viral assembly 6. Release

Answer 623

Biosafety Level 2

Answer 624

Nucleic acid composition ## Footnote True viruses have nucleic acid that is either RNA or DNA, and this serves as the basis for initial classification.

Answer 625

Adenovirus

Answer 626

Human fibroblast cells

Answer 627

Herpes simplex virus ## Footnote Stomatitis is an inflammation of the mucous membranes of the oral cavity. Herpes simplex virus is the primary agent of this disease, in which multiple ulcerative lesions are seen on the oral mucosa.

Answer 628

Parvovirus B19

Answer 629

Parvovirus B19

Answer 630

Papillomavirus

Answer 631

BK virus—urine

Answer 632

Progressive multifocal leukoencephalopathy ## Footnote BK VIRUS: Hemorrhagic cystitis JC VIRUS: Progressive multifocal leukoencephalopathy

Answer 633

Pox viruses

Answer 634

Human herpes virus 8

Answer 635

Respiratory syncytial virus (RSV)

Answer 636

Parainfluenza, RSV, and metapneumovirus ## Footnote CROUP: Inflammation of upper airways (larynx, trachea) with respiratory obstruction, often caused by virus infections in children.

Answer 637

Parotid glands (salivary gland)

Answer 638

Mumps virus

Answer 639

Enteroviruses

Answer 640

Rhinoviruses

Answer 641

Coxsackie virus

Answer 642

Norwalk-like viruses

Answer 643

Rabies virus

Answer 644

Respiratory

Answer 645

Infection control measures, including isolation and wearing of protective gear

Answer 646

Jump of an animal coronavirus into humans ## Footnote The SARS virus probably originated in a nonhuman host, most likely bats, was amplified in palm civets, and was transmitted to humans in live animal markets. Chinese horseshoe bats are natural reservoirs of SARS-like coronaviruses.

Answer 647

Candida albicans ## Footnote C. albicans is the common cause of oral thrush involving the mucocutaneous membranes of the mouth. C. albicans is part of the normal flora of the skin, mucous membranes, and gastrointestinal tract.

Answer 648

Trichophyton mentagrophytes ## Footnote T. mentagrophytes, a common cause of athletes’ foot, is sometimes confused with T. rubrum, the most common dermatophyte to infect humans. T. mentagrophytes: urease +, hair perforation + T. rubrum: urease negative, hair perforation negative

Answer 649

CMV ## Footnote CMV infection in young adults causes a self-limited mononucleosis syndrome. CMV infections are common and usually self-limited, except in neonates and immunosuppressed patients, in whom they may cause a life-threatening situation.

Answer 650

Immediately test the patient and the student for using an EIA or ELISA test ## Footnote With the permission of the patient (state law may require him or her to sign a consent form) and counseling of the student nurse, the appropriate course of action is to test the patient for HIV using a screening test (EIA or ELISA). The student should also be baseline tested. If the test result is positive for the patient, the student is administered the appropriate antiviral drug(s) immediately or within 2 hours of the incident. Confirmatory testing is done on any positive HIV tests.

Answer 651

Herpes simplex testing ## Footnote Herpes genitalis is an infection caused by HSV-2. Symptomatic primary herpes by HSV-2 is responsible for about 85% of herpes infections. HSV-1 (causing the other 15%) does not involve recurring infections of herpes and causes fever blisters. HSV-2 causes 99% of recurrent genital herpes.

Assessment MICRO Flashcards

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