BACTE Flashcards by MS ICA

Flocked swab:

Cotton
Gauze
Cotton and gauze
Nylon

Nylon

NYLON STRANDS ARE SPRAYED OR FLOCKED ONTO THE TIP.

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The steam autoclave method of sterilization:

Uses 15 lbs of pressure for 15 minutes
Utilizes dry heat for 20 minutes
Produces a maximum temperature of 100ºC
Requires a source of ethylene oxide

Uses 15 lbs of pressure for 15 minutes

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.

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The most important diagnostic tool in treating patients with clinical infections in the emergency department:

AFB stain
Culture
Gram stain
IMVic reaction

Gram stain

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Additional tests to be included with the IMViC reaction:

Bacitracin and SXT susceptibility
Catalase and coagulase
Motility and H2S
Oxidase and urease

Motility and H2S

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.

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Salmonella Shigella (SS) Agar is a modification of:

BAP
CAP
DCA
EMB

DCA

Salmonella Shigella (SS) Agar is a modification of the Deoxycholate Citrate Agar.

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Cary-Blair indicator changes from red to yellow color:

Buffering capacity was overcomed
Change in the pH of the medium
Low temperature
Presence of contaminants

Buffering capacity was overcomed

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.

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When cultured in thioglycollate broth, these organisms grow slightly below the surface where oxygen concentrations are lower than atmospheric concentrations

Aerotolerant anaerobes
Facultative anaerobes
Microaerophilic organisms
Obligate aerobes

Microaerophilic organisms

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.

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Which one of the following specimen requests is acceptable?

Feces submitted for anaerobic culture
Foley catheter tip submitted for aerobic culture
Rectal swab submitted for direct smear for gonococci
Urine for culture of acid-fast bacilli

Urine for culture of acid-fast bacilli

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.

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Which of the following is the most appropriate method for collecting a urine specimen from a patient with an indwelling catheter?

Remove the catheter, cut the tip, and submit it for culture
Disconnect the catheter from the bag, and collect urine from the terminal end of the catheter
Collect urine directly from the bag
Aspirate urine aseptically from the catheter tubing

Aspirate urine aseptically from the catheter tubing

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).

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A liquid fecal specimen from a three-month-old infant is submitted for microbiological examination. In addition to culture on routine media for Salmonella and Shigella, this specimen should be routinely:

Examined for the presence of Entamoeba hartmanni
Examined for the presence of Camylobacter sp
Screened for the detection of enterotoxigenic Escherichia coli
Placed in thioglycollate broth to detect Clostridium
botulinum

Examined for the presence of Camylobacter sp

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.

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Composition of 0.5 McFarland standard:

1% sulfuric acid and 2.175% barium chloride
1% sulfuric acid and 1.175% barium chloride
1% hydrochloric acid and 2.175% barium chloride
1% hydrochloric acid and 1.175% barium chloride

1% sulfuric acid and 1.175% barium chloride

0.5 McFarland (barium sulfate) standard:
1% sulfuric acid
1.175% barium chloride

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Standard agar depth of the Mueller-Hinton agar:

1 to 2 mm
3 to 5 mm
6 to 8 mm
7 to 9 mm

3 to 5 mm

MUELLER-HINTON AGAR
STANDARD AGAR DEPTH
3 to 5 mm. (average of 4 mm.)

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Susceptibility testing performed on quality control organisms using a new media lot number yielded zone sizes that were too large for all antibiotics tested. The testing was repeated using media from a previously used lot number, and all zone sizes were acceptable. Which of the following best explains the unacceptable zone sizes?

The antibiotic disks were not stored with the proper desiccant
The depth of the media was too thick
The depth of the media was too thin
The antibiotic disks were not properly applied to the media

The depth of the media was too thin

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Quality control results for disk diffusion susceptibility tests yield the following results: aminoglycoside zones too small and penicillin zones too large. This is most likely due to the:

Inoculum being too heavy
Inoculum being too light
pH of Mueller-Hinton agar being too low
Calcium and magnesium concentration in the agar being too high

pH of Mueller-Hinton agar being too low

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.

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In disk diffusion susceptibility testing, as an antimicrobial agent diffuses away from the disk, the concentration of antibiotic is:

Increased
Decreased
Unchanged
Inoculum dependent

Decreased

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

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After satisfactory performance of daily disk diffusion susceptibility quality control is documented, the frequency of quality control can be reduced to:

Twice a week
Every week
Every other week
Every month

Every week

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.

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An outbreak of Staphylococcus aureus has occurred in a hospital nursery. In order to establish the epidemiological source of the outbreak, the most commonly used typing method is:

Pulsed-field gel electrophoresis
Serological typing
Coagulase testing
Catalase testing

Pulsed-field gel electrophoresis

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

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The organism most commonly associated with neonatal purulent meningitis is:

N. meningitidis
S. pneumoniae
S. agalactiae
S. pyogenes

S. agalactiae

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

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One of the enterotoxins produced by enterotoxigenic Escherichia coli in traveler’s diarrhea is similar to a toxin produced by:

Clostridium perfringens
Clostridium difficile
Vibrio cholerae
Yersinia enterocolitica

Vibrio cholerae

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

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Which of the following sets of tests best differentiates Salmonella and Citrobacter species?

KCN, malonate, beta-galactosidase, lysine decarboxylase
Dulcitol, citrate, indole, H2S production
Lactose, adonitol, KCN, motility
Lysine decarboxylase, lactose, sucrose, malonate, indole

KCN, malonate, beta-galactosidase, lysine decarboxylase

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.

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The Oriental rat flea, Xenopsylla cheopis, can be involved in transmitting which of the following microorganisms?

Bartonella quintana
Plasmodium spp.
Rickettsia prowazeki
Yersinia pestis

Yersinia pestis

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Oxidase positive, urease negative:

Bordetella bronchiseptica
Bordetella pertussis
Bordetella parapertussis
All of these

Bordetella pertussis

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A culture from an infected dog bite on a small boy’s finger yielded a small, gram-negative coccobacillus that was smooth, raised and beta-hemolytic on blood agar. The isolate grew on MacConkey agar, forming colorless colonies. The organism was motile, catalase positive, oxidase positive, reduced nitrate, and was urease positive within 4 hours. No carbohydrates were fermented. The most likely identification of this isolate is:

Brucella canis
Yersinia pestis
Francisella tularensis
Bordetella bronchiseptica

Bordetella bronchiseptica

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.

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While swimming in a lake near his home, a young boy cut his foot, and an infection developed. The culture grew a nonfastidious gram-negative, oxidase positive, beta hemolytic, motile bacilli that produced deoxyribonuclease. The most likely identification is:

Enterobacter cloacae
Serratia marcescens
Aeromonas hydrophila
Escherichia coli

Aeromonas hydrophila

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.

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A community hospital microbiology laboratory is processing significant numbers of stool cultures because of an outbreak of diarrhea following heavy rains and flooding in the country. A media that should be incorporated in the plating protocol is: Colistin nalidixic acid for Listeria MacConkey agar with sorbitol for Campylobacter Mannitol salt agar for Enterococcus species Thiosulfate citrate bile salts sucrose for Vibrio species

Thiosulfate citrate bile salts sucrose for Vibrio species 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.

Stool specimens suspected of containing Vibrio spp. should be collected and transported only in: Amies medium Cary-Blair medium Stuart's medium Transgrow medium

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

Catalase positive, lactose negative, xylose positive: Haemophilus aegypticus Haemophilus ducreyi Haemophilus parainfluenzae Haemophilus influenzae

Haemophilus influenzae

The best procedure to differentiate Listeria monocytogenes from Corynebacterium species is: Catalase Motility at 25C Motility at 35C Gram stain

Motility at 25C 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.

A patient has a suspected diagnosis of subacute bacterial endocarditis. His blood cultures grow non-spore-forming pleomorphic gram-positive bacilli only in the anaerobic bottle. What test(s) will give a presumptive identification of this microorganism? Beta-hemolysis and oxidase Catalase and spot indole Esculin hydrolysis Gelatin hydrolysis

Catalase and spot indole 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.

Colonies appear shiny and mucoid because of the presence of a polysaccharide capsule: Candida albicans Cryptococcus neoformans Malassezia furfur Histoplasma capsulatum

Cryptococcus neoformans

LATEX AGGLUTINATION for cryptococcal _____ is now recommended test for Cryptococcus neoformans. Polysaccharide capsule Antigen Antibody Nucleic acids

Antigen

A mold grown at 25C exhibited delicate septate hyaline hyphae and many conidiophores extending at right angles from the hyphae. Oval, 2-5 um conidia were formed at the end of the conidiophores giving a flowerlike appearance. In some areas “sleeves” of spores could be found along the hyphae as well. A 37C culture of this organism produced small, cigar-shaped yeast cells. This organism is most likely: Histoplasma capsulatum Sporothrix schenckii Blastomyces dermatitidis Coccidioides immitis

Sporothrix schenckii

Virulence factors include aflatoxin, serine protease and aspartic acid proteinase: Aspergillus spp. Blastomyces dermatitidis Cryptococcus neoformans Histoplasma capsulatum

Aspergillus spp.

Most often, ______ are “dead-end” hosts. Amphibians Birds Humans Rodents

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

Delay in the processing of fluid specimens requires dilution in a viral transport medium before storage: 1: 2 to 1:5 1:10 to 1:20 1:50 to 1:100 1:100 to 1:200

1: 2 to 1:5

The most sensitive method for the detection of β-lactamase in bacteria is by the use of: Chromogenic cephalosporin Penicillin Oxidase Chloramphenicol acetyltransferase

Chromogenic cephalosporin

According to the Kirby–Bauer standard antimicrobial susceptibility testing method, what should be done when interpreting the zone size of a motile, swarming organism such as Proteus species? The swarming area should be ignored The results of the disk diffusion method are invalid The swarming area should be measured as the growth boundary The isolate should be retested after diluting to a 0.05 McFarland standard

The swarming area should be ignored

Antimicrobial susceptibility testing of anaerobes is done by which of the following methods? Broth disk elution Disk agar diffusion Microtube broth dilution β-Lactamase testing

Microtube broth dilution 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.

Cerebrospinal fluid (CSF) should be cultured immediately, but if delayed the specimen should be: Refrigerated at 4°C to 6°C Frozen at –20°C Stored at room temperature for no longer than 24 hours Incubated at 37°C and cultured as soon as possible

Incubated at 37°C and cultured as soon as possible

Select the method of choice for recovery of anaerobic bacteria from a deep abscess. Cotton fiber swab of the abscess area Skin snip of the surface tissue Needle aspirate after surface decontamination Swab of the scalpel used for débridement

Needle aspirate after surface decontamination

Anaerobic bacteria are routinely isolated from all of the following types of infections except: Lung abscesses Brain abscesses Dental infections Urinary tract infections

Urinary tract infections 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).

Prereduced and vitamin K1-supplemented blood agar plates are recommended isolation media for: Mycobacterium marinum and Mycobacterium avium intracellulare Bacteroides, Peptostreptococcus, and Clostridium spp. Proteus spp. Enterococcus spp.

Bacteroides, Peptostreptococcus, and Clostridium spp. 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.

Which of the following is the medium of choice for the selective recovery of gram-negative anaerobes? Kanamycin–vancomycin (KV) agar Phenylethyl alcohol (PEA) agar Cycloserine–cefoxitin–fructose agar (CCFA) THIO broth

Kanamycin–vancomycin (KV) agar

Methods other than packaged microsystems used to identify anaerobes include: Antimicrobial susceptibility testing Gas–liquid chromatography (GLC) Special staining Enzyme immunoassay

Gas–liquid chromatography (GLC) 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.

Semisolid transport media such as Amies, Stuart, or Cary–Blair are suitable for the transport of swabs for culture of most pathogens except: Neisseria gonorrhoeae Enterobacteriaceae Campylobacter fetus Streptococcus pneumoniae

Neisseria gonorrhoeae

Colistin–nalidixic acid agar (CNA) is used primarily for the recovery of: Neisseria species Enterobacteriaceae Pseudomonas aeruginosa Staphylococcus aureus

Staphylococcus aureus

Toxic shock syndrome is attributed to infection with: Staphylococcus epidermidis Staphylococcus hominis Staphylococcus aureus Staphylococcus saprophyticus

Staphylococcus aureus

Which Staphylococcus species, in addition to S. aureus, also produces coagulase? S. intermedius S. saprophyticus S. hominis All of these options

S. intermedius

An isolate of Staphylococcus aureus was cultured from an ulcer obtained from the leg of a diabetic79-year-old female patient. The organism showed resistance to methicillin. Additionally, this isolate should be tested for resistance or susceptibility to: Erythromycin Gentamicin Vancomycin Kanamycin

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

Resistance to which drug categorizes a strain of Staphylococcus aureus as methicillin-resistant Staphylococcus aureus (MRSA)? Oxacillin Colistin Trimethoprim–sulfamethoxazole Tetracycline

Oxacillin 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.

Which test is used for the determination of inducible clindamycin resistance in staphylococci and streptococci? E-test D-zone test A-test CAMP test

D-zone test

An outbreak of Staphylococcus aureus in the nursery department prompted the Infection Control Committee to proceed with an environmental screening procedure. The best screening media to use for this purpose would be: CNA agar THIO broth Mannitol salt agar PEA agar

Mannitol salt agar

Streptococcus species exhibit which of the following properties? Aerobic, oxidase positive, and catalase positive Facultative anaerobe, oxidase negative, catalase negative Facultative anaerobe, β-hemolytic, catalase positive May be α-, β-, or γ-hemolytic, catalase positive

Facultative anaerobe, oxidase negative, catalase negative

An isolate recovered from a vaginal culture obtained from a 25-year-old female patient who is 8 months pregnant is shown to be a gram-positive cocci, catalase negative, and β-hemolytic on blood agar. Which tests are needed for further identification? Optochin, bile solubility, PYR Bacitracin, CAMP, PYR Methicillin, PYR, trehalose Coagulase, glucose, PYR

Bacitracin, CAMP, PYR 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.

The bile solubility test causes the lysis of: Streptococcus bovis colonies on a blood agar plate Streptococcus pneumoniae colonies on a blood agar plate Group A streptococci in broth culture Group B streptococci in broth culture

Streptococcus pneumoniae colonies on a blood agar plate

Nutritionally variant streptococci (NVS) require specific thiol compounds, cysteine, or the active form of vitamin B6. Which of the following tests supplies these requirements? CAMP test Bacitracin susceptibility test Bile solubility test Staphylococcal cross-streak test

Staphylococcal cross-streak test

All of the following are appropriate when attempting to isolate N. gonorrhoeae from a genital specimen except: Transport the genital swab in charcoal transport medium Plate the specimen on modified Thayer–Martin (MTM) medium Plate the specimen on New York City or Martin-Lewis agar Culture specimens in ambient oxygen at 37°C

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

A Gram stain of a urethral discharge from a man showing extracellular and intracellular gram-negative diplococci within segmented neutrophils is a presumptive identification for: Neisseria gonorrhoeae Neisseria meningitidis Moraxella (Branhamella) catarrhalis Neisseria lactamica

Neisseria gonorrhoeae

The β-galactosidase test aids in the identification of which Neisseria species? N. lactamica N. meningitidis N. gonorrhoeae N. flavescens

N. lactamica

Deoxycholate agar (DCA) is useful for the isolation of: Enterobacteriaceae Enterococcus spp. Staphylococcus spp. Neisseria spp.

Enterobacteriaceae

Xylose lysine deoxycholate (XLD) agar is a highly selective medium used for the recovery of which bacteria? Staphylococcus spp. from normal flora Yersinia spp. that do not grow on Hektoen agar Enterobacteriaceae from gastrointestinal specimens Streptococcus spp. from stool cultures

Enterobacteriaceae from gastrointestinal specimens

The Voges–Proskauer (VP) test detects which end product of glucose fermentation? Acetoin Nitrite Acetic acid Hydrogen sulfide

Acetoin

At which pH does the methyl red (MR) test become positive? 7.0 6.5 6.0 4.5

4.5

The ortho-nitrophenyl-β-galactopyranoside(ONPG) test is most useful when differentiating: Salmonella spp. from Pseudomonas spp. Shigella spp. from some strains of Escherichia coli Klebsiella spp. from Enterobacter spp. Proteus vulgaris from Salmonella spp.

Shigella spp. from some strains of Escherichia coli

In the test for urease production, ammonia reacts to form which product? Ammonium citrate Ammonium carbonate Ammonium oxalate Ammonium nitrate

Ammonium carbonate 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.

Which of the following reagents is added to detect the production of indole? p-Dimethylaminobenzaldehyde Bromcresol purple Methyl red Cytochrome oxidase

p-Dimethylaminobenzaldehyde

Decarboxylation of the amino acids lysine, ornithine, and arginine results in the formation of: Ammonia Urea CO2 Amines

Amines

Putrescine is an alkaline amine product of which bacterial enzyme? Arginine decarboxylase Phenylalanine deaminase Ornithine decarboxylase Lysine decarboxylase

Ornithine decarboxylase

Which genera are positive for phenylalanine deaminase Enterobacter, Escherichia, and Salmonella Morganella, Providencia, and Proteus Klebsiella and Enterobacter Proteus, Escherichia, and Shigella

Morganella, Providencia, and Proteus

Biochemically, the Enterobacteriaceae are gram-negative rods that: Ferment glucose, reduce nitrate to nitrite, and are oxidase negative Ferment glucose, produce indophenol oxidase, and form gas Ferment lactose and reduce nitrite to nitrogen gas Ferment lactose and produce indophenol oxidase

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

Care must be taken when identifying biochemical isolates of Shigella because serological cross-reactions occur with: E. coli Salmonella spp. Pseudomonas spp. Proteus spp.

E. coli

Which of the following tests best differentiates Shigella species from E. coli? Hydrogen sulfide, VP, citrate, and urease Lactose, indole, ONPG, and motility Hydrogen sulfide, MR, citrate, and urease Gas, citrate, and VP

Lactose, indole, ONPG, and motility 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.

Fever, abdominal cramping, watery stools, and fluid and electrolyte loss preceded by bloody stools 2–3 days before is characteristic of shigellosis but may also result from infection with: Campylobacter spp. Salmonella spp. Proteus spp. Yersinia spp.

Campylobacter spp. 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.

A gram-negative rod is recovered from a catheterized urine sample from a nursing home patient. The lactose-negative isolate tested positive for indole, urease, ornithine decarboxylase, and phenylalanine deaminase and negative for H2S.The most probable identification is: Edwardsiella spp. Morganella spp. Ewingella spp. Shigella spp.

Morganella spp.

The Shiga-like toxin (verotoxin) is produced mainly by which Enterobacteriaceae? Klebsiella pneumoniae E. coli Salmonella typhimurium Enterobacter cloacae

E. coli

Following a 2-week camping trip to the Southwest (US), a 65-year-old male patient was hospitalized with a high fever and an inflammatory swelling of the axilla and groin lymph nodes. Several blood cultures were obtained, resulting in growth of gram-negative rods resembling “closed safety pins.” The organism grew on MacConkey’s agar showing non–lactose-fermenting colonies. Testing demonstrated a nonmotile rod that was biochemically inert. What is the most likely identification? Yersinia pestis Klebsiella pneumoniae Proteus vulgaris Morganella morganii

Yersinia pestis

The majority of clinical laboratories with a microbiology department should have the capability of serotyping which pathogenic Enterobacteriaceae? Yersinia enterocolitica, Shigella spp. E. coli O157:H7, Salmonella spp., Shigella spp. Yersinia pestis, Salmonella spp. Edwardsiella spp., Salmonella spp.

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

The drugs of choice for treatment of infections with Enterobacteriaceae are: Aminoglycosides, trimethoprim–sulfamethoxazole, third-generation cephalosporins Ampicillin and nalidixic acid Streptomycin and isoniazid Chloramphenicol, ampicillin, and colistin

Aminoglycosides, trimethoprim–sulfamethoxazole, third-generation cephalosporins

Which isolates of the Enterobacteriaceae family most commonly produce extended-spectrumβ-lactamase (ESBL)? E. coli and Klebsiella pneumoniae Yersinia enterocolitica and Yersinia pestis Morganella morganii and Proteus vulgaris Salmonella typhi and Shigella sonnei

E. coli and Klebsiella pneumoniae

Which test group best differentiates Acinetobacter baumannii from P. aeruginosa? Oxidase, motility, NO3 reduction MacConkey growth, 37°C growth, catalase Blood agar growth, oxidase, catalase Oxidase, TSI, MacConkey growth

Oxidase, motility, NO3 reduction 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.

Which organism is associated with immunodeficiency syndromes and melioidosis (a glanders-like disease in Southeast Asia and northern Australia)? Pseudomonas aeruginosa Pseudomonas stutzeri Pseudomonas putida Burkholderia pseudomallei

Burkholderia pseudomallei

Which biochemical tests are needed to differentiate Burkholderia cepacia from S. maltophilia? Pigment on blood agar, oxidase, DNase Pigment on MacConkey agar, flagellar stain, motility Glucose, maltose, lysine decarboxylase TSI, motility, oxidase

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

Alcaligenes faecalis (formerly A. odorans) is distinguished from Bordetella bronchiseptica with which test? Urease (rapid) Oxidase Growth on MacConkey agar Motility

Urease (rapid) 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.

Alcaligenes faecalis (formerly A. odorans) is distinguished from Bordetella bronchiseptica with which test? Urease (rapid) Oxidase Growth on MacConkey agar Motility

Cetrimide agar is used as a selective isolation agar for which organism? Acinetobacter spp. Pseudomonas aeruginosa Moraxella spp. Stenotrophomonas maltophilia

Pseudomonas aeruginosa

Cetrimide agar is used as a selective isolation agar for which organism? Acinetobacter spp. Pseudomonas aeruginosa Moraxella spp. Stenotrophomonas maltophilia

Pseudomonas aeruginosa

Which of the listed Pseudomonas spp. is associated with the following virulence factors: exotoxin A, endotoxins, proteolytic enzymes, antimicrobial resistance, and production of alginate? P. fluorescens P. putida P. stutzeri P. aeruginosa

P. aeruginosa

Select the media of choice for recovery of Vibrio cholerae from a stool specimen. MacConkey agar and thioglycollate media Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth Blood agar and selenite-F (SEL) broth CNA agar

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

Abdominal pain, fever, vomiting, and nausea prompted an elderly male to seek medical attention. A watery stool specimen producing no fecal leukocytes or erythrocytes was cultured and grew a predominance of gram-negative fermentative bacilli. The colonies were beta-hemolytic on blood agar and cream colored on MacConkey agar. The colonies were both oxidase and catalase positive. What is the most likely identification? Aeromonas hydrophilia Escherichia coli Salmonella spp. Shigella spp.

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

Several attendees of a medical conference in the Gulf coast area became ill after frequenting a seafood restaurant. A presumptive identification of Vibrio cholera was made after stool specimens from several subjects grew clear colonies on MacConkey agar and yellow colonies on TCBS agar. Which key tests would help eliminate Aeromonas and Plesiomonas spp.? Mannitol fermentation, Na+ requirement Oxidase, motility Oxidase, nitrate Hemolysis on blood agar, catalase

Mannitol fermentation, Na+ requirement 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.

Which of the following tests should be done first in order to differentiate Aeromonas spp. from the Enterobacteriaceae? Urease OF glucose Oxidase Catalase

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

Which atmospheric condition is needed to recover Campylobacter spp. from specimens inoculated onto a Campy-selective agar at 35°C–37°C and 42°C? 5% O2, 10% CO2, and 85% N2 20% O2, 10% CO2, and 70% N2 20% O2, 20% CO2, and 60% N2 20% O2, 5% CO2, and 75% N2

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

Which group of tests best differentiates Helicobacter pylori from C. jejuni? Catalase, oxidase, and Gram stain Catalase, oxidase, and nalidixic acid sensitivity Catalase, oxidase, and cephalothin sensitivity Urease, nitrate, and hippurate hydrolysis

Urease, nitrate, and hippurate hydrolysis

Smooth gray colonies showing no hemolysis are recovered from an infected cat scratch on blood and chocolate agar but fail to grow on MacConkey agar. The organisms are gram-negative pleomorphic rods that are both catalase and oxidase positive and strongly indole positive. The most likely organism is: Capnocytophaga spp. Pasteurella spp. Proteus spp. Pseudomonas spp

Pasteurella spp.

A 29-year-old male who often hunted rabbits and spent a lot of time in the woods was admitted to the hospital with skin ulcers on his upper extremities. At 48 hours, a small coccobacillus was recovered from the aerobic blood culture bottle only. The organism stained poorly with Gram stain, but did stain with acridine orange. Cultures taken from the ulcers did not grow on primary media. What is the most likely identification? Pseudomonas aeruginosa Pseudomonas fluorescens Chryseobacterium spp. Francisella tularensis

Francisella tularensis

An elderly woman who cared for several domestic cats was hospitalized with suspected cat-scratch disease (CSD). Blood cultures appeared negative, but a small, slightly curved pleomorphic gram-negative bacillus grew on BHI agar (brain, heart infusion agar with 5% horse or rabbit blood). What is the most likely identification? Bartonella spp. Brucella spp. Kingella spp. Haemophilus spp

Bartonella spp.

A neonate was readmitted to the hospital with a diagnosis of meningitis. The CSF revealed gram-negative straight rods. At 24 hours, the organism grew on 5% sheep blood and chocolate agars displaying a yellow pigment. On MacConkey agar, it appeared as a non–lactose fermenter. Colonies were oxidase, DNase, and gelatinase positive, and oxidized glucose and mannitol. What is the most likely identification? Haemophilus influenza Chryseobacterium meningosepticum Stenotrophomonas maltophilia Acinetobacter baumannii

Chryseobacterium meningosepticum

A 46-year-old dog warden was admitted to the hospital with several puncture bite wounds encountered while wrangling with a stray dog. Culture at 48 hours produced small yellow colonies on 5% sheep blood and chocolate agars in10% CO2, but no growth on MacConkey agar. Gram stain showed gram-negative curved, fusiform rods. Colonies were oxidase and catalase positive. What is the most likely identification? Capnocytophaga canimorsus Francisella tularensis Legionella pneumophila Pseudomonas aeruginosa

Capnocytophaga canimorsus 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.

A suspected case of Legionnaires’ disease was noted on the request form for a culture and sensitivity ordered on a sputum sample. The patient was a 70-year-old male who presented with a positive serological test for Legionella spp. What is the most efficient way to confirm the infection using the submitted sample? Culture the sputum on MacConkey agar Gram stain of the sputum Acid-fast staining Direct immunofluorescent microscopy

Direct immunofluorescent microscopy 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.

Which of the following organisms will display lipase activity on egg yolk agar? Clostridium botulinum Clostridium sporogenes Clostridium novyi (A) All of these options

All of these options

Identification of Clostridium tetani is based upon: Gram stain of the wound site Anaerobic culture of the wound site Blood culture results Clinical findings

Clinical findings 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.

Cycloserine–cefoxitin-fructose agar (CCFA) is used for the recovery of: Yersinia enterocolitica Yersinia intermedia Clostridium perfringens Clostridium difficile

Clostridium difficile

The gram-positive non–spore-forming anaerobic rods most frequently recovered from blood cultures as a contaminant are: Propionibacterium acnes Clostridium perfringens Staphylococcus intermedius Veillonella parvula

Propionibacterium acnes 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.

A flexible calcium alginate nasopharyngeal swab is the collection device of choice for recovery of: Staphylococcus aureus Streptococcus pneumoniae Corynebacterium diphtheriae Bacteroides fragilis

Corynebacterium diphtheriae

Acid-fast staining of a smear prepared from digested sputum showed slender, slightly curved, beaded, red mycobacterial rods. Growth on Middlebrook 7H10 slants produced buff-colored microcolonies with a serpentine pattern after 14 days at 37°C. Niacin and nitrate reduction tests were positive. What is the most probable presumptive identification? Mycobacterium tuberculosis Mycobacterium ulcerans Mycobacterium kansasii Mycobacterium avium–intracellulare complex

Mycobacterium tuberculosis 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.

Individuals showing a positive purified protein derivative (PPD) skin test for M. tuberculosis are usually: Infective Symptomatic of pulmonary disease Latently infected Falsely positive

Latently infected 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.

Which mycobacterium is associated with Crohn’s disease? M. marinum M. paratuberculosis M. avium M. gordonae

M. paratuberculosis

Routine laboratory testing for Treponema pallidum involves: Culturing Serological analysis Acid-fast staining Gram staining

Serological analysis 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.

Which organism typically produces “fried-egg” colonies on agar within 1–5 days of culture from a genital specimen? Mycoplasma hominis Borrelia burgdorferi Leptospira interrogans Treponema pallidum

Mycoplasma hominis

Which procedure is appropriate for culture of genital specimens in order to recover Chlamydia spp.? Inoculate cycloheximide-treated McCoy cells Plate onto blood and chocolate agar Inoculate into thioglycollate (THIO) broth Plate onto modified Thayer–Martin agar within 24 hours

Inoculate cycloheximide-treated McCoy cells

Which of the following organisms are transmitted to animals and humans after a tick bite? Leptospira Chlamydia and Mycoplasma spp. Neisseria sicca Ehrlichia and Anaplasma spp.

Ehrlichia and Anaplasma spp.

What is the first step to be performed in the identification of an unknown yeast isolate? Gram stain smear India ink stain Catalase test Germ tube test

Germ tube test

The Hair Baiting Test is used to differentiate which two species of Trichophyton that produce red colonies on Sabouraud agar plates? T. mentagrophytes and T. rubrum T. tonsurans and T. schoenleinii T. tonsurans and T. violaceum T. verrucosum and T. rubrum

T. mentagrophytes and T. rubrum

An India ink test was performed on CSF from an HIV-infected male patient. Many encapsulated yeast cells were seen in the centrifuged sample. Further testing revealed a positive urease test and growth of brown colonies on niger-seed agar. The diagnosis of meningitis was caused by which yeast? Candida albicans Cryptococcus neoformans Cryptococcus laurentii Candida tropicalis

Cryptococcus neoformans

After a vacation to the Southwestern United States, a midwesterner complained of flulike symptoms with fever, chills, nonproductive cough, and chest pain. Microscopic exam of sputum, cleared with KOH, revealed large, thick-walled spherules containing endospores. Upon culture, the mold phase showed septate hyphae and alternating barrel-shaped arthroconidia. Which organism is most likely the cause of thispneumonia? Coccidioides immitis Histoplasma capsulatum Paracoccidioides brasiliensis Penicillium marneffei

Coccidioides immitis

Specimens for virus culture should be transported in media containing: Antibiotics and 5% sheep blood Saline and 5% sheep blood 22% bovine albumin Antibiotics and nutrient

Antibiotics and nutrient 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.

Which virus belonging to the Reoviridae group causes gastroenteritis in infants and young children but an asymptomatic infection in adults? Coxsackie B virus Rotavirus Respiratory syncytial virus Rhabdovirus

Rotavirus

A 40-year-old female experienced a respiratory infection after returning home from a visit to her homeland of China. A rapid onset of pneumonia in the lower respiratory area prompted the physician to place her in isolation. She was diagnosed presumptively with severe acute respiratory syndrome (SARS) and placed on a respirator. What type of testing should be done next to diagnose this disease? Molecular technique and cell culture Latex agglutination test Blood culture Complement fixation

Molecular technique and cell culture