levinson questions Flashcards
1
Q
clinical case 14: a 40 yo woman has blurred vision and slurred speech. she is afebrile. sie is famous in her neighborhood for her home-canned vegetables and fruits.
diagnosis?
A
botulism caused by clostridium botulinum. botulinum toxin causes a descending paralysis that starts with the cranial nerves, typically appearing initially as diplopia. the toxin is a protease that cleaves the proteins involved in release of acetylcholine at the neuromuscular junction. treat with antiserum immediately. confirm diagnosis with mouse protection test using a sample of food suspected of containing the toxin. wound botulism occurs in heroin users, especially in those who “skin pop.”
2
Q
clinical case 42: a 20 yo man fell off his motorcycle and suffered a compound fracture of the femur. the fracture was surgically reduced and the wound was debrided. forty-eight hours later, he spiked a fever and the wound are became necrotic. crepitus was felt, and a foul-smelling odor was perceived originating from the wound. makred anemia and a white blood count of 22,800 were found. gram stain of the exudate showed large gram-positive rods. colonies grew on blood agar incubated anaerobically but not aerobically.
diagnosis?
A
gas gangrene cause by clostridium perfringens. the main virulence factor produced by this organism is an exotoxin that is a lecithinase. it causes necrosis of tissue and lysis of rbcs. the spores of the organisms are in the soil and enter at the wound site. a foul-smelling exudate is characteristic of infections caused by anaerobic bacteria.
3
Q
28: each of the following statements concerning exotoxins is correct except:
A: when treated chemically, some exotoxins lose their toxicity and can be used as immunogens in vaccines
B: some exotoxins are capable of causing disease in purified form, free of any bacteria
C: some exotoxins act in the GI tract to cause diarrhea
D: some exotoxins contain lipopolysaccharides as the toxic component
A
D
4
Q
33: each of the following statements concerning exotoxins is correct except:
A: exotoxins are polypeptides
B: exotoxins are more easily inactivated by heat than are endotoxins
C: exotoxins are less toxic than the same amount of endotoxins
D: exotoxins can be converted to toxoids
A
C
5
Q
A: diphtheria toxin B: tetanus toxin C: botulinum toxin D: toxic shock syndrome toxin E: cholera toxin
47: causes paralysis by blocking release of AcH
A
C
6
Q
A: diphtheria toxin B: tetanus toxin C: botulinum toxin D: toxic shock syndrome toxin E: cholera toxin
48: inhibits protein synthesis by blocking elongation factor 2
A
A
7
Q
A: diphtheria toxin B: tetanus toxin C: botulinum toxin D: toxic shock syndrome toxin E: cholera toxin
49: stimulates T cells to produce cytokines
A
D
8
Q
A: diphtheria toxin B: tetanus toxin C: botulinum toxin D: toxic shock syndrome toxin E: cholera toxin
50: stimulates the production of cyclic AMP by adding ADP-ribose to a G protein
A
E
9
Q
A: diphtheria toxin B: tetanus toxin C: botulinum toxin D: toxic shock syndrome toxin E: cholera toxin
51: inhibits the release of inhibitory neurotransmitters causing muscle spasms
A
B
10
Q
65: the most important protective function of the antibody stimulated by tetanus immunization is:
A: to opsonize the pathogen (clostridium tetani)
B: to prevent growth of the pathogen
C: to prevent adherence of the pathogen
D: to neutralize the toxin of the pathogen
A
D
11
Q
82: the pathogenesis of which one of the following organisms is most likely to involve invasion of the intestinal mucosa?
A: vibrio cholerae
B: shigella sonnei
C: enterotoxigenic escherichia coli
D: clostridium botulinum
A
B
12
Q
86: each of the following statements concerning clostridia is correct except:
A: pathogenic clostridia are found both in the soil and in the normal flora of the colon
B: antibiotic-associated (pseudomembranous) colitis is due to a toxin produced by C. Difficile
C: anaerobic conditions at the wound site are not required to cause tetanus, because spores will form in the presence of oxygen
D: botulism, which is caused by ingesting preformed toxin, can be prevented by boiling food prior to eating
A
C
13
Q
111: each of the following statements concerning exotoxins is correct except:
A: some strains of escherichia coli produce an enterotoxin that causes diarrhea
B: cholera toxin acts by stimulating adenylate cyclase
C: diphtheria is caused by an exotoxin that inhibits protein synthesis by inactivating an elongation factor
D: botulism is caused by a toxin that hydrolyzes lecithin (lecithinase), thereby destroying nerve cells
A
D
14
Q
122: each of the following statements concerning clostridium perfringens is correct except:
A: it causes gas gangrene
B: it causes food poisioning
C: it produces an exotoxin that degrades lecithin and causes necrosis and hemolysis
D: it is a gram-negative rod that does not ferment lactose
A
D
15
Q
123: each of the following statements concerning clostridium tetani is correct except:
A: it is a gram-positive, spore forming rod
B: pathogenesis is due to the production of an exotoxin that blocks inhibitory neurotransmitters
C: it is a facultative organism; it will grow on a blood agar plate in the presence of room air
D: its natural habitat is primarily the soil
A
C
16
Q
127: which one of the following statements concerning immunization against diseases caused by clostridia is correct?
A: antitoxin against tetanus protects against botulism as well, because the two toxins share antigenetic sites
B: vaccines containing alpha toxin (lecithinase) are effective in protecting against gas gangrene
C: the toxoid vaccine against c. diff. infection should be administered to the immunocompromised
D: immunization with tetanus toxoid induces effective protection against tetanus toxin
A
D
17
Q
130: each of the following statements concerning wound infections caused by Clostridium perfringens is correct except:
A: an exotoxin plays a role in pathogenesis
B: gram-positive rods are found in the exudate
C: the organism grows only in human cell culture
D: anaerobic culture of the wound site should be ordered
A
C
18
Q
clinical case questions, case 26:
your patient is a 70 yo man with a fever of 40 C and a very painful cellulitis of the right buttock. the skin appears necrotic, and there are several fluid-filled bullae. creptius can be felt, indicating gas in the tissue. a gram stain of the exudate reveals large gram-positive rods
of the following, which one is the most likely cause?
A: clostridium perfringens
B: bacillus anthracis
C: corynebacterium diphtheriae
D: actinomyces israelii
A
A
19
Q
PE II: 11
a 6 yo boy fell and sustained a deep wound from a rusty nail that penetrated his thigh. his mother removed the nail and cleaned the wound with soap and water. the next morning, he had a temp of 102 F and his thigh was very painful and swollen. in the ER, crepitus was noted. a gram stain of exudate revealed large gram positive rods. which one of the following is the most likely cause?
A: actinomyces israelii B: clostricium perfringens C: clostridium tetani D: listeria monocytogenes E: mycobacterium fortuitumchelonei complex F: nocardia asteroides G: pseudomonas aeruginosa
A
B
20
Q
10: each of the following statements concerning the normal flora is correct except:
A: the most common organism found on the skin is staphylococcus epidermidis
B: escherichia coli is a prominent member of the normal flora of the throat
C: the major site where bacteroides fragilis is found is the colon
D: one of the most common sites where staphylococcus aureus is found is the nose
A
B
21
Q
36: each of hte following statements concerning the normal flora is correct except:
A: the normal flora of the colon consists predominantly of anaerobic bacteria
B: the presence of the normal flora prevents certain pathogens from colonizing the upper respiratory tract
C: fungi (eg yeasts) are not members of the normal flora
D: organisms of the normal flora are permanent residents of the body surfaces
A
C
22
Q
38: each of the following statements concerning the normal flora is correct except:
A: streptococcus mutans is found in the mouth and contributes to the formation of dental caries
B: the predominant organisms in the alveoli are viridans streptococci
C: bacteroides frangilis is found in greater numbers than escherichia coli in the colon
D: candida albicans is part of the normal flora of both men and women
A
B
23
Q
55: each of the following organisms is an important cause of UTI except:
A: escherichia coli
B: proteus mirabilis
C: klebsiella pneumoniae
D: bacteroides fragilis
A
D
24
Q
56: your patient is a 30 yo woman with nonbloody diarrhea for the past 14 hours. which one of the following organisms is least likely to cause this illness?
A: clostridium difficile
B: streptococcus pyogenes
C: shigella dysenteriae
D: salmonella enteritidis
A
B
25
58: a 50 yo homeless alcoholic has a fever and is coughing up 1 cup of green, foul-smelling sputum per day. you suspect that he may have a lung abscess. which one of the following pairs of organisms is most likely to be the cause?
A: listeria monocytogenes and legionella pneumophila
B: nocardia asteroides and mycoplasma pneumoniae
C: fusobacterium nucleatum and peptostreptococcus intermedius
D: clostridium perfringens and chlamydia psittaci
C
26
64: which one of the following host defense mechanisms is the most important for preventing dysentery caused by salmonella?
A: gastric acid
B: salivary enzymes
C: normal flora of the mouth
D: alpha interferon
A
27
75: your patient is a 70 yo man who underwent bowel surgery for colon cancer 3 days ago. he now has a fever and abdominal pain. you are concerned that he may have peritonitis. which one of the following pairs of organisms is most likely to be the cause?
A: bacteroides fragilis and klebsiella pneumoniae
B: bordetella pertussis and salmonella enteritidis
C: actinomyces israelii and campylobacter jejuni
D: clostridium botulinum and shigella dysenteriae
A
28
79: your patient has a brain abscess that was detected 1 month after a dental extraction. which one of the following organisms is most likely to be involved?
A: anaerobic streptococci
B: mycobacterium smegmatis
C: lactobacillus acidophilus
D: mycoplasma pneumoniae
A
29
87: each of the following statements concerning bacteroides fragilis is correct except:
A: B. fragilis is a gram-negative rod that is part of the normal flora of the colon
B: B. fragilis forms endospores, which allow it to survive in the soil
C: the capsule of B. fragilis is an important virulence factor
D: B. fragilis infections are characterized by foul-smelling pus
B
30
92: five days ago a 65 yo woman with a lower UTI began taking ampicillin. she now has a fever and severe diarrhea. of the organisms listed, which one is the most likely to be the cause of the diarrhea?
A: clostridium difficile
B: bacteroides fragilis
C: proteus mirabilis
D: bordetella pertussis
A
31
105: each of the following statements concerning actinomyces and nocardia is correct except:
A: a. israelii is an anaerobic rod found as part of the normal flora in the mouth
B: both actinomyces and nocardia are branching, filamentous rods
C: N. asteroides causes infections primarily in immunocompromised patients
D: infections are usually diagnosed by detecting a significant rise in antibody titer
D
32
A: bacteroides fragilis
B: haemophilus influenzae
C: pseudomonas aeruginosa
D: chlamydia pneumoniae
158: anaerobic gram-negative rod that is an important cause of peritonitis
A
33
extended matching: 560: causes peritonitis; is an obligate anaerobe
```
A: escherichia coli
B: shigella sonnei
C: salmonella typhi
D: salmonella enteritidis
E: proteus mirabilis
F: pseudomonas aeruginosa
G: vibrio cholerae
H: campylobacter jejuni
I: helicobacter pylori
J: bacteroides fragiis
```
J
34
clinical case questions case 9:
your patient is a 27 yo woman who was treated with oral ampicillin for cellulitis caused by strep. pyogenes. several days later, she developed bloody diarrhea. you suspect that she may have pseudomembanous colitis.
regarding the causative organism of pseudomembranous colitis, which one of the following is the most accurate?
A: it is an aerobic gram-positive rod that produces exotoxins
B: it is a common-shaped gram-negative rod that grows best at 41 C
C: it is an obligate intracellular parasite that grows in cell culture but not on blood agar
D: it is a yeast that forms germ tubes when incubated in human serum at 37 C
A
35
clinical case questions case 15:
your patient is a 20 yo man who was in a fist fight and suffered a broken jaw and lost two teeth. several weeks later, he developed an abscess at the site of the trauma that drained to the surface of the skin, and yellowish granules were seen in the pus.
regarding this disease, which one of the following is most accurate?
A: the causative organism is a gram-positive rod that forms long filaments
B: the causative organism is a comma-shaped gram-negative rod that produces an exotoxin which increases cyclic AMP
C: the causative organism cannot be seen in the gram stain but can be seen in an acid-fast stain
D: a combination of gram-negative cocci and spirochetes cause this disease
A
36
clinical case questions case 26:
your patient is a 70 yo man with a fever of 40 C and a very painful cellulits of the right buttock. the skin appears necrotic, and there are several fluid-filled bullae. crepitus can be felt, indicating gas in the tissue. a gram stain of the exudate reveals large gram-positive rods
of the following, which one is the most likely cause?
A: clostridium perfringens
B: bacillus anthracis
C: corynebacterium diphtheriae
D: actinomyces israelii
A
37
clinical case questions case 40:
your patient is a 40 yo woman with systemic lupus erythematosus who is being treated with high-dose prednisone during a flare of her disease. she develops a fever to 38 C and a cough productive of a small amount of greenish sputum. on physical examination, you hear coarse breath sounds in the left lower lobe. chest xray reveals an infiltrate in that region. gram stain of the sputum reveals long filaments of gram-positive rods.
which one of the following organisms is the most likely cause of this disease?
A: mycobacterium kansasii
B: listeria monocytogenes
C: nocardia asteroides
D: mycoplasma pneumoniae
C
38
clinical case questions case 43:
your patient is a 62 yo woman with a history of carcinoma of the sigmoid colon that was removed 5 days ago. the surgery was complicated by the escape of bowel contents into the peritoneal cavity. she now has fever and pain in the perineum and left buttock. on physical examination, her temp is 39 C and myonecrosis with a foul-smelling discharge is found. a gram stain of the exudate reveals gram-negative rods
of the following, which one is the most likely organism to cause this infection?
A: helicobacter pylori
B: bacteroides fragilis
C: salmonella typhi
D: vibrio parahaemolyticus
B
39
PE II: 16
an 80 yo man had a carcinoma of the colon removed 3 days ago. he was doing well until this morning, when he spiked a fever to 39 C and complained of severe abdominal pain. examination revealed a boardlike abdomen indicative of peritonitis. he was taken to the OR where it was discovered that his anastomosis had broken down and bowel contents had spilled into the peritoneal cavity. a foul-smelling exudate was observed. a gram stain of the peritoneal exudate revealed many gram-negative rods. which one of the following sets of bacteria is the most likely cause of this infection?
A: escherichia coli and brucella melitensis
B: enterobacter cloacae and salmonella enteritidis
C: fusobacterium nucleatum and bacteroides ragilis
D: haemophilus influenzae and actinomyces israelii
E: shigella dysenteriae and serratia marcescens
C
40
clinical case 5: a 12 yo boy has a painful arm that he thought he had injured while pitching in a little league baseball game. the pain has gotten worse over a 2-week period, and he now has a temperature of 100 F. X-ray of the humerus reveals raised periosteum. aspirate of lesion reveals gram positive cocci in clusters.
diagnosis?
osteomyelitis caused by staphylococcus aureus. this organism is the most common cause of osteomyelitis in children. osteomyelitis in prosthethic joints is often caused by staph. epidermidis.
41
clinical case 24: a 34 yo man was in his usual state of health until last night, when he felt feverish, had a shaking chill, and became short of breath at rest. T 39 C, BP 110/60, P 104, R 18. scattered rales were heard in both bases. a new murmur consistent with tricuspid insufficiency was heard. needle tracks were seen on both forearms. gram-positive cocci in clusters grew in blood culture.
diagnosis?
acute endocarditis caused by staph. aureus. this organism is the most common cause of acute endocarditis in IV drug users. the valves on the right side of the heart are often involved
42
clinical case 30: a 24 yo woman experienced the sudden onset of high fever, myalgias, vomiting, and diarrhea. her vital signs were T 40 C, BP 70/30, P 140, R 30. A sunburn-like rash appeared over most of her body. blood cultures and stool cultures are negative. she is recovering from a surgical procedure on her maxillary sinus and the bleeding was being staunched with nasal tampons. gram positive cocci in clusters were seen in blood adherent to the nasal tampon.
diagnosis?
toxic shock syndrome caused by staph aureus. toxic shock syndrome toxin is a superantigen that stimulates the release of large amounts of cytokines from many helper T cells
43
```
A: diphtheria toxin
B: tetanus toxin
C: botulinum toxin
D: toxic shock syndrome toxin
E: cholera toxin
```
49: stimulates T cells to produce cytokines
D
44
52: an outbreak of sepsis caused by staph. aureus has occurred in the newborn nursery. you are called upon to investigate. according to your knowledge of the normal flora, what is the most likely source of the organism?
A: colon
B: nose
C: throat
D: vagina
B
45
62: the coagulase test, in which the bacteria cause plasma to clot, is used to distinguish:
A: streptococcus pyogenes from enterococcus faecalis
B: streptococcus pyogenes from staphylococcus aureus
C: staphylococcus aureus from staphylococcus epidermidis
D: staphylococcus epidermidis from neisseria meningitidis
C
46
63: which one of the following is a virulence factor for staphylococcus aureus?
A: a heat-labile toxin that inhibits glycine release at the inter-nuncial neuron
B: an oxygen-labile hemolysin
C: resistance to novobiocin
D: protein A that binds to the Fc portion of IgG
D
47
74: each of the following statements concerning staphylococcus aureus is correct except:
A: gram-positive cocci in grape-like clusters are seen on gram-stained smear
B: the coagulase test is positive
C: treatment should include a beta-lactamase resistant penicillin
D: endotoxin is an important pathogenic factor
D
48
78: two hours after a delicious thanksgiving dinner of barley soup, roast turkey, stuffing, sweet potato, green beans, cranberry sauce, and pumpkin pie topped with whipped cream, the Smith family of four experience vomiting and diarrhea. which one of the following organisms is most likely to cause these symptoms?
A: shigella flexneri
B: campylobacter jejuni
C: staphylococcus aureus
D: salmonella enteritidis
C
49
88: each of the following statements concerning staphylococci is correct except:
A: S. aureus is differentiated from S. epidermidis by the production of coagulase
B: S. aureus infections are often associated with abscess formation
C: the majority of clinical isolates of S. aureus produce penicillinase; therefore, penicillin G should not be used for antibiotic therapy for S. aureus infections
D: scalded skin syndrome caused by S. aureus is due to enzymatic degradation of epidermal desmosomes by catalase
D
50
93: the pathogenesis of which one of the following diseases does not involve an exotoxin?
A: scarlet fever
B: typhoid fever
C: toxic shock syndrome
D: botulism
B
51
107: tissue degrading enzymes play an important role in the pathogenesis of several bacteria. which one of the following is not involved in tissue or cell damage?
A: lecithinase of clostridium perfringens
B: hyaluronidase of streptococcus pyogenes
C: M protein of streptococcus pneumoniae
D: leukocidin of staphylococcus aureus
C
52
116: each of the following statements concerning enterotoxins is correct except:
A: enterotoxins typically cause bloody diarrhea with leukocytes in the stool
B: staphylococcus aureus produces an enterotoxin that causes vomiting and diarrhea
C: vibrio cholerae causes cholera by producing an enterotoxin that increases adenylate cyclase activity within the enterocyte
D: escherichia coli enterotoxin mediates ADP-ribosylation of a G protein
A
53
120: which one of the following organisms causes diarrhea by producing an enterotoxin that increases adenylate cyclase activity within enterocytes?
A: escherichia coli
B: bacteroides fragilis
C: staphylococcus aureus
D: enterococcus faecalis
A
54
extended matching 543: causes fever an shock by binding to the T cell receptor
```
A: toxic shock syndrome
B: tetanus toxin
C: diphtheria toxin
D: cholera toxin
E: coagulase
F: botulinium toxin
G: alpha toxin of C. perfringens
H: M protein
I: endotoxin
J: verotoxin
```
A
55
CCQ: case 10
your patient is a 10 yo girl who has had pain in her left arm from the past 5 days. on physical examination, her temperature is 38 C and there is tenderness of the humerus near her deltoid. on x ray of the humerus, an area of raised periosteum and erosion of bone is seen. you do a blood culture
which one of the following is the most likely set of findings?
A: gram negative rods that grow on EMB agar, forming purple colonies and a green sheen
B: gram positive cocci that grow on blood agar, causing a clear zone of hemolysis and are coagulase-positive
C: gram-positive rods that grow only anaerobically and form a double zone of hemolysis on blood agar
D: gram-negative diplococci that grow on blood agar, are oxidase-positive, and ferment maltose
B
56
CCQ: case 13
Ms. Jones calls to say that she, her husband, and their child have nausea and vomiting for the past hour or so. also, they have had some nonbloody diarrhea. you ask when their last meal together was, and she says they had a picnic lunch about 3 hours ago. they have no fever.
which one of the following is the most likely finding?
A: gram stain of the leftover food would show many gram-positive cocci in clusters
B: gram stain of the stool would show many gram-negative diplococci
C: KOH prep of the leftover food would show many budding yeasts
D: acid fast stain of the stool would show many acid fast rods
A
57
CCQ: case 19
your patient is a 10 yo girl who has leukemia and is receiving chemotherapy through an indwelling venous catheter. she now has a fever of 39 C but is otherwise asymptomatic. you do a blood culture, and the laboratory reports growth of staph. epidermidis
which on of the following results is least likely to be found by the clinical laboratory?
A: gram-positive cocci in clusters were seen on gram stain of the blood culture
B: subculture of the blood culture onto blood agar revealed nonhemolytic colonies
C: a coagulase test on the colonies was negative
D: a catalase test on the colonies was negative
D
58
CCQ: case 25
your patient is a 3 yo girl with fever and pain in her right ear. on physical examination, the drum is found to be perforated, and a bloody exudate is seen. a gram stain of the exudate reveals gram-positive diplococci
of the following, which one is the most likely cause?
A: strep. pyogenes
B: staph. aureus
C: corynebacterium diphtheriae
D: strep. pneumonia
D
59
PE I: 1
a 9 yo girl was playing soccer when she began to limp. she has a pain in her leg and points to her upper thigh when asked where it hurts. her temp is 101 F. xray of the femur reveals that the periosteum is eroded. you order a blood culture. which one of the following would be the most likely blood culture findings?
A: gram-negative rods that grow on EMB agar, forming purple colonies and a green sheen
B: gram-positive cocci that grow on blood agar, causing a clear zone of hemolysis, and are coagulase-positive
C: gram-positive rods that grow only anaerobically and form a double zone of hemolysis on blood agar
D: gram-negative diplococci that grow on chocolate agar, are oxidase-positive, and ferment maltose
E: gram-positive cocci that grow on blood agar, causing a green zone of hemolysis, and are not inhibited by optochin and bile
B
60
PE I: 3
a 25 yo man has a history of four episodes of boils in the last year. boils are abscesses caused by staph. aureus. which one of the following is most likely to be the underlying immunologic factor that predisposes him to multiple episodes of boils?
A: a deficient amount of the C8 component of complement in his plasma
B: an inability of his macrophages to present antigen in association with class I MHC proteins
C: a failure to release granzymes from his cytotoxic T cells
D: an insufficient amount of IgG in his plasma
D
61
PE 1: 34
an outbreak of post-surgical wound infections caused by staph. aureus has occurred. the infection control team was asked to determine whether the organism could be carried by one of the OR personnel. using your knowledge of normal flora, which one of the following body sites is the most likely location for this organism?
```
A: colon
B: gingival crevice
C: nose
D: throat
E: vagina
```
C
62
PE 2: 21
a 65 yo woman had symptoms of dementia. an mri revealed significant cortical atrophy. it was determined that her intraventricular pressure was very high, and a ventriculoperitoneal shunt was placed to relieve the pressure. three weeks later she developed a fever to 38 C and anorexia but no other symptoms. of the following, which one best describes the most likely organism causing her current symptoms?
A: a gram-positive coccus that does not clot plasma
B: a curved gram-negative rod that produces urease
C: an acid-fast rod that does not grow on bacteriologic media
D: an obligate intracellular parasite that forms a cytoplasmic inclusion body
E: a spirochete that induces an antibody that agglutinates a lipid from a cow's heart
A
63
PE 2: 31
a 25 yo man was in a motorcycle accident 3 days ago, in which he sustained severe head trauma. he has had spinal fluid leaking from his nose since the accident and now develops a severe headache. his temperature is 39 C and on examination you find nuchal rigidity. you do a lumbar puncture and find that the spinal fluid is cloudy and contains 5000 WBC/uL, 90% of which are polys. of the following, which one is the most likely result observed in the lab analysis of the spinal fluid?
A: gram negative rods that grew only anaerobically
B: a motile spirochete that formed beta-hemolytic colonies on blood agar
C: gram-positive cocci that formed alpha hemolytic colonies on blood agar
D: gram positive cocci that grew only in the presence of 6.5% sodium chloride
E: gram positive rods that grew only on chocolate agar supplemented with X and V factors
F: no organism was seen using gram stain, but tissue stains revealed cytoplasmic inclusion bodies
C
64
CC 16
a 14 yo girl has a rapidly spreading, painful, erythematous rash on her leg. the rash is warm and tender, and her temp is 38 C. gram positive cocci in chains were seen in an aspirate from the lesion. culture of the aspirate on blood agar grew colonies surrounded by clear (beta) hemolysis. growth of the organism was inhibited by bacitracin
diagnosis?
celluitis caused by strep. pyogenes. rapid spread is due to hyaluronidase (spreading factor) that degrades hyaluronic acid in subcutaneous tissue. acute glomerulonephirits can folllow skin infecitons = an immunologic disease caused by antigen-antibody complexes
65
13: of the following choices, the most important function fo antibody in host defenses against bacteria is:
A: activation of lysozyme that degrades the cell wall
B: acceleration of proteolysis of exotoxins
C: facilitation of phagocytosis
D: inhibition of bacterial protein synthesis
C
66
```
A: diphtheria toxin
B: tetanus toxin
C: botulinum toxin
D: toxic shock syndrome toxin
E: cholera toxin
```
50: stimulates the production of cyclic AMP by adding ADP-ribose to a G protein
E
67
53: each of the statements about the classification of strep. is correct except:
A: pneumococci (strep. pneumoniae) are alpha hemolytic and can be serotyped on the basis of their polysaccharide capsules
B: enterococci are group D sterptococci and can be classified by their ability to grow in 6.5% sodium chloride
C: although pnuemococci and the viridans streptococci are alpha hemolytic, they can be differentiated by the bile solubility test and their susceptibility to optochin
D: viridans streptococci are identified by Lancefield grouping, which is based on the C carbohydrate in the cell wall
D
68
54: each of the following agents is a recognized cause of diarrhea except:
A: clostridium perfringens
B: enterococcus faecalis
C: escherichia coli
D: vibrio cholerae
B
69
60: your patient has subacute bacterial endocarditis caused by a member of the viridans group of strep. which one of the following is the most likely to be the source of the organism?
A: skin
B: colon
C: oropharynx
D: urethra
C
70
61: a culture of skin lesions from a patient with pyoderma shows numerous colonies surrounded by a zone of beta hemolysis on a blood agar plate. a gram stained smear shows gram-positive cocci. if you found the catalase test to be negative, which one of the following organisms would you most probably have isolated?
A: strep. pyogenes
B: staph. aureus
C: staph. epidermidis
D: strep. pneumoniae
A
71
66: five hours after eating fried rice at a restaurant, a 24 yo woman and her husband both developed nausea, vomiting, and diarrhea. which one of the following organisms is the most likely to be involved?
A: clostridium perfringens
B: enterotoxigenic escherichia coli
C: bacillus cereus
D: salmonella typhi
C
72
76: a 65 yo man develops dysuria and hematuria. a gram stain of a urine sample shows gram- negative rods. culture of the urine on EMB agar reveals lactose-negative colonies without evidence of swarming motility. which one of the following organisms is most likely to be the cause of UTI?
A: enterococcus faecalis
B: pseudomonas aeruginosa
C: proteus vulgaris
D: escherichia coli
B
73
80: the most important contribution of the capsule of strep pneumoniae to virulence is:
A: to prevent dehydration of the organisms on mucosal surfaces
B: to retard phagocytosis by polymophonuclear leukocytes
C: to inhibit polymorphonuclear leukocyte chemotaxis
D: to accelerate tissue invasion by its collagenase-like activity
B
74
81: the most important way the host counteracts the function of the pneumococcal polysaccharide capsule is via:
A: t lymphocytes sensitized to polysaccharide agents
B: polysaccharide degrading enzymes
C: anticapsular antibody
D: activated macrophages
C
75
89: acute glomerulonephritis is a nonsuppurative complication that follows infection by which one of the following organisms?
A: enterococcus faecalis
B: streptococcus pyogenes
C: streptococcus pneumoniae
D: streptococcus agalactiae
B
76
91: a 70 yo man is found to have a hard mass in his prostate, which is suspected to be a carcinoma. 24 hours after surgical removal of the mass, he develops fever to 39 C and has several shaking chills. of the organisms listed, which one is least likely to be involved?
A: escherichia coli
B: enterococcus faecalis
C: klebsiella pneumoniae
D: legionella pneumophila
D
77
94: regarding the effect of benzyl-penicillin (penicillin G) on bacteria, which one of the following organisms is least likely to be resistant?
A: staphylococcus aureus
B: enterococcus faecalis
C: streptococcus pyogenes
D: neisseria gonorrheoeae
C
78
100: which one of the following is not an important characteristic of strep. pyogenes?
A: protein A
B: M protein
C: beta-hemolysin
D: polysaccharide group-specific substance
A
79
101: each of the following is associated with the lancefield group B strep (S. agalactiae) except?
A: pyoderma (impetigo)
B: vaginal carriage in 5% to 25% of normal women of child-bearing age
C: neonatal sepsis and meningitis
D: beta-hemolysis
A
80
102: three organisms, strep. pneumonia, neisseria menigitidis, and haemophilus influenzae, cause the vast majority of of cases of bacterial meningitis. what is the most important pathogenic component they share?
A: protein A
B: capsule
C: endotoxin
D: beta-lactamase
B
81
107: tissue-degrading enzymes play an important role in the pathogenesis of several bacteria. which one of the following is not involved in tissue or cell damage?
A: lecithinase of clostridium perfringes
B: hyaluronidase of streptococcus pyogenes
C: M protein of strep pneumoniae
D: leukocidin of staph aureus
C
82
109: which one of the following organisms is the most frequent bacterial cause of pharyngitis?
A: staph. aureus
B: strep. pneumnoniae
C: strep. pyogenes
D: neisseria meningitidis
C
83
A: corynebacterium diphtheriae
B: listeria monocytogenes
C: bacillus anthracis
D: clostridium botulinum
144: causes both skin lesions and a severe pneumonia
C
84
A: corynebacterium diphtheriae
B: listeria monocytogenes
C: bacillus anthracis
D: clostridium botulinum
145: causes flaccid paralysis
D
85
A: corynebacterium diphtheriae
B: listeria monocytogenes
C: bacillus anthracis
D: clostridium botulinum
146: causes a pseudomembrane in the throat, which can cause respiratory tract obstruction
A
86
A: corynebacterium diphtheriae
B: listeria monocytogenes
C: bacillus anthracis
D: clostridium botulinum
147: causes menigitis in neonates and the immunocompromised
B
87
A: staph. aureus
B: strep. pyogenes
C: enterococcus faecalis
D: strep. pneumoniae
151: grows in 6.5% sodium choloride
C
88
A: staph. aureus
B: strep. pyogenes
C: enterococcus faecalis
D: strep. pneumoniae
152: is bile soluble
D
89
A: staph. aureus
B: strep. pyogenes
C: enterococcus faecalis
D: strep. pneumoniae
153: produces enterotoxin
A
90
A: staph. aureus
B: strep. pyogenes
C: enterococcus faecalis
D: strep. pneumoniae
154: is associated with rheumatic fever
B
91
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 551
the vaccine contains a single serotype of a capsular polysaccharide coupled to a protein carrier
C
92
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 552
immunogen in the vaccine is a toxoid
G
93
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 553
causes acute glomerulonephritis; is beta hemolytic
B
94
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 554
causes UTI grows in 6.5% NaCl
F
95
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 555
causes neonatal meningitis; is bacitracin-resistant
J
96
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 556
causes meningitis in adults; is alpha hemolytic and optochin sensitive
A
97
```
A: strep. pneumoniae
B: strep. pyogenes
C: haemophilus influenzae
D: salmonella typhi
E: staph. aureus
F: enterococcus faecalis
G: clostridium tetani
H: bordetella pertussis
I: escherichia coli
J: strep. agalactiae
K: staph. epidermidis
L: strep. mutans
```
EM 557
causes food poisoning; is coagulase positive
E
98
CCQ 1
your patient is a 10 yo woman with the sudden onset of fever to 104 and a severe headache. physical examination reveals nuchal rigidity. you suspect meningitis and do a spinal tap. gram stain of the spinal fluid reveals many neutrophils and many gram negative diplococci
of the following bacteria, which one is most likely to be the cause?
A: haemophilus influenzae
B: neisseria meningitidis
C: streptococcus pneumoniae
D: pseudomonas aeruginosa
B
99
CCQ 7
your patient is a 22 yo man with fever, fatique, and a new diastolic murmur. you suspect endocarditis and do a blood culture.
which one of the following statements is least accurate?
A: if he had dental surgery recently, one of the most likely organisms to grow would be a viridans group strep.
B: if he is an IV drug user, one of the most likely organisms to grow would be candida albicans
C: if he had colon surgery recently, one of the most likely organisms to grow would be enterococcus faecalis
D: if he has a prosthetic aortic valve, one of the most likely organisms to grow would be strep. agalactiae
D
100
CCQ 8
your patient is a 70 yo woman who had a histerectomy for carcinoma of the uterus 3 days ago. she has an indwelling urinary catheter in place and now has a fever to 39 C and the urine in the collection bottle is cloudy. a gram stain of the urine specimen shows many neutrophils and gram-positive cocci in chains. you also do a urine culture.
which one of the following is the most likely set of findings on the urine culture?
A: beta hemolytic colonies that are bacitracin-sensitive
B: alpha hemolytic colonies that are optochin-sensitive
C: nonhemolytic colonies that grow in 6.5% sodium chloride
D: nonhemolytic colonies that grow only anaerobically
C
101
CCQ 12
your patient is a 12 yo boy who is receiving chemotherapy for acute leukemia. he develops fever, headache, and a stiff neck, and you make a presumptive diagnosis of menigitis and do a lumbar puncture. a gram stain reveals a small gram positive rod, and a culture of the spinal fluid grows a beta hemolytic colony on blood agar
regarding this organism, which one of the following is most accurate?
A: it has more than 100 serologic types
B: it produces an exotoxin that inhibits elongation factor 2
C: it is commonly acquired by eating unpasterurized dairy products
D: there is a toxoid vaccine available against the organism
C
102
CCQ 17
your patient is a 25 yo woman with a sore throat since yesterday. on physical exam, her throat is red, but no exudate is seen. two enlarged tender cervical lymph nodes are palpable. her temp is 101 F. a throat culture reveals no beta hemolytic colonies. after receiving this result, you do another physical examination, which reveals an enlarged spleen. a heterophil antibody test finds that sheep red blood cells are agglutinated by the patient's serum.
which one of the following is the most likely cause of this disease?
A: strep. pyogenes
B: corynebacterium diphtheriae
C: EBV
D: influenza virus
C
103
CCQ 18
your patient is a 15 yo boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. you make a clinical diagnosis of rheumatic fever.
which one of the following laboratory results is most likely to be found in this patient?
A: a blood culture is positive for strep pyogenes at this time
B: a throat culture is positive for strep. pyogenes at this time
C: a gram stain of the joint fluid shows gram-positive cocci in chains at this time
D: an anti-strepolysin O assay is positive at this time
D
104
CCQ 30
your patient is a 20 yo man with a sore throat for the past 3 days. on physical exam, his temp is 38 C, the pharynx is red, and several tender submaxillary nodes are palpable
of the following, which one is the most likely organism to cause this infection?
A: strep. agalactiae (group B strep)
B: strep. sanguis (a viridans groups strep.)
C: parvovirus B19
D: EBV
D
105
CCQ 31
your patient is a 55 yo woman with a lymphoma who is receiving chemo. via IV catheter. she suddenly develops fever, shaking, chills and hypotension
of the following, which one is the least likely organism to cause this infection?
A: strep. pneumoniae
B: klebsiella pneumoniae
C: mycoplasma pneumoniae
D: proteus mirabilis
C
106
CCQ 33
your patient is a 78 yo man who had an episode of acute urinary retention and had to be cathetarized. he then underwent cystoscopy to determine the cause of the retention. two days later, he developed fever and suprapubic pain. urinalysis revealed 50 WBC adn 10 RBC per high power field. culture of the urine revealed a thin film of bacterial growth over the entire blood agar plate, and the urease test was positive
which one of the following is the most likely organism to cause this infection?
A: escherichia coli
B: proteus mirabilis
C: strep. faecalis
D: branhamella (moraxella) catarrhalis
B
107
CCQ 38
your patient is a 6 yo boy with papular and pustular skin lesions on his face. a serous, honey-colored fluid exudes from the lesions. you suspect impetigo. a gram stain of the pus reveals many neutrophils and gram positive cocci in chains.
if you cultured the pus on blood agar, which one of the following would you be most likely to see?
A: small beta hemolytic colonies containing bacteria that are bacitracin sensitive
B: small alpha hemolytic colonies containing bacteria that are resistant to optochin
C: large nonhemolytic colonies containing bacteria that are oxidase-positive
D: small nonhemolytic colonies containing bacteria that grow in 6.5% nacl
A
108
CCQ 50
your patient is a 10 yo boy who fell, abraded the skin of his thigh, and developed cellulitis (the skin was red, hot, and tender). several days later, the infection was treated with a topical antibiotic ointment, and the cellulitis gradually healed. however, 2 weeks later, he told his mother that his urine was cloudy and reddish, and she noted that his face was swollen. you suspect acute glomerulonephirits
regarding the causative organism, what is the most likely appearance of a gram stain of the exudate from the skin infection?
A: gram positive cocci in grapelike clusters
B: gram positive cocci in chains
C: gram positive diplococci
D: gram negative diplococci
B
109
PE 1 16
a 70 yo woman presents with rapid onset of fever to 39 C and a cough productive of greenish sputum. she is not hospitalized and not immunocompromised. a chest x ray reveals a left lower lobe infiltrate. of the following, which set of findings describes the most likely causative organism found in the sputum culture?
A: gram-positive diplococci that form an alpha-hemolytic colony
B: gram-negative diplococci that form an oxidase-positive colony
C: gram-positive rods that form a beta hemolytic colony
D: gram-negative rods that form an oxidase-positive colony
E: gram-negative cocci that grow only anaerobically
A
110
PE 1 21
a 25 yo pregnant woman in the third trimester comes to the emergency room saying that about 12 hours ago she began to feel feverish and weak. on examination, her temp is 40 C but no other pertinent findings. a blood culture grows small gram positive rods that cause beta hemolysis on a blood agar plate incubated in room air. which one of the following bacteria is the most likely cause?
```
A: clostridium perfringens
B: strep. pyogenes
C: bacillus cereus
D: listeria monocytogenes
E: brucella abortus
```
D
111
PE 1 26
a 60 yo woman had surgery for ovarian carcinoma 4 days ago and has an indwelling urinary catheter in place. she now spikes a fever to 39 C and has cloudy urine in the collection bottle. gram stain of the urine shows many polys and gram-positive cocci in chains. which one of the following would be the most likely finding in the urine culture?
A: alpha-hemolytic colonies on the blood agar plate that are optochin-sensitive
B: beta-hemolytic colonies on the blood agar plate that are bacitracin-sensitive
C: beta-hemolytic colonies on the blood agar plate that hydrolyze hippurate
D: nonhemolytic colonies on the blood agar plate that grow in 6.5% sodium choride
D
112
PE 2 1
a 4 yo girl has papular and pustular lesions on her face. the lesions are exuding a honey-colored serous fluid. you make a clinical diagnosis of impetigo. a gram stain of the exudate reveals gram-positive cocci in chains, and a culture reveals beta-hemolytic colonies on blood agar. for which one of the following sequelae is she most at risk?
```
A: bloody diarrhea
B: blurred vision
C: paralysis of the facial nerve (bell's palsy)
D: RBCs and albumin in her urine
E: rusty-colored sputum
```
D
113
PE 2 28
a 30 yo woman with a previous history of rheumatic fever now has a fever for the past 2 weeks. physical examination reveals a new heart murmur. you suspect endocarditis and do a blood culture, which grows a viridans group strep later identified as strep sanguis. of the following body sites, which one is the most likely source of this organism?
```
A: colon
B: mouth
C: skin
D: stomach
E: vagina
```
B
114
CCQ 1
your patient is a 10 yo woman with the sudden onset of fever to 104 and a severe headache. physical examination reveals nuchal rigidity. you suspect meningitis and do a spinal tap. gram stain of the spinal fluid reveals many neutrophils and many gram negative diplococci
additional history reveals she has had several serious infections with this organism (neisseria menigitidis) before. on the basis of this, which one of the following is the most likely predisposing factor?
A: HIV
B: deficient in CD8+ T cells
C: deficient in one of the late-acting complement components
D: deficient in antigen presentation by macrophages
C
115
CCQ 18
your patient is a 15 yo boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. you make a clinical diagnosis of rheumatic fever.
which one of the following modes of pathogenesis is most compatible with a diagnosis of rheumatic fever?
A: bacteria attach to joint and heart tissue via pili, invade and cause inflammation
B: bacteria secrete exotoxins that circulate via the blood to the joints and heart
C: bacterial antigens induce antibodies that cross-react with joint and heart tissue
D: bacterial exotoxin induces interleukin-1 and tumor necrosis factor, which cause inflammation in joint and heart tissue
C
116
CCQ 18
your patient is a 15 yo boy with migratory polyarthritis, fever, and a new, loud cardiac murmur. you make a clinical diagnosis of rheumatic fever.
which one of the following approaches is most likely to prevent endocarditis in patients with rheumatic fever?
A: they should take the streptococcal polysaccharide vaccine
B: they should take penicillin if they have dental surgery
C: they should take the toxoid vaccine every 5 years
D: they should take rifampin if they have abdominal surgery
B
117
CCQ 30
your patient is a 20 yo man with a sore throat for the past 3 days. on physical exam, his temp is 38 C, the pharynx is red, and several tender submaxillary nodes are palpable
you do a throat culture and many small translucent colonies that are beta hemolytic on grow on blood agar. gram stain of one of these colonies reveals gram positive cocci in chains
of the following, which one is the most likely organism to cause this infection?
A: strep. pneumoniae
B: strep. pyogenes
C: strep. agalactiae (group B strep)
D: peptostreptococcus species
B
118
CCQ 31
your patient is a 55 yo woman with a lymphoma who is receiving chemo. via IV catheter. she suddenly develops fever, shaking, chills and hypotension
if a blood culture drawn from the patient grows a gram negative rod, which one of the following is the least likely organism to cause this infection?
A: bordetella pertussis
B: escherichia coli
C: pseudonomas aeruginosa
D: serratia marcescens
A
119
CCQ 31
your patient is a 55 yo woman with a lymphoma who is receiving chemo. via IV catheter. she suddenly develops fever, shaking, chills and hypotension
of the following virulence factors, which one is the most likely to cause the fever and hypotension seen in the patient described?
A: pilus
B: capsule
C: lecithinase
D: lipopolysaccharide
D
120
CCQ 50
your patient is a 10 yo boy who fell, abraded the skin of his thigh, and developed cellulitis (the skin was red, hot, and tender). several days later, the infection was treated with a topical antibiotic ointment, and the cellulitis gradually healed. however, 2 weeks later, he told his mother that his urine was cloudy and reddish, and she noted that his face was swollen. you suspect acute glomerulonephirits
what is the pathogenesis of the cloudy urine and facial swelling?
A: toxin-mediated
B: direct invasion by the bacteria
C: immune complex mediated
D: cell mediated immunity (delayed hypersensitivity)
C
121
each of the following statements concerning mycobacterium tuberculosis is correct except:
A: after being stained with carbolfuchsin, m tb resists decoloration with acid alcohol
B: M. tb has a large amount of mycolic acid in its cell wall
C: M tb appears as a red rod in gram-stained specimens
D: m. tb appears as a red rod in acid-fast stained specimens
C
122
59: which one of the following diseases is best diagnosed by sero-logic means?
A: Q fever
B: pulmonary tb
C: gonorrhea
D: actinomycosis
A
123
108: the soil is the natural habitat for certain microorganisms of medical importance. which one of the following is least likely to reside there?
A: clostridium tetani
B: mycobacterium aviumintracellulare
C: bacillus anthracis
D: chlamydia trachomatis
D
124
126: each of the following statements concerning mycobacterium tuberculosis is correct except:
A: some strains of M. TB isolated from patients exhibit multiple drug resistance (resistant to both isoniazid and rifampin)
B: M. TB contains a small amount of lipid in its cell wall and therefore stains poorly with the gram stain
C: M. TB grows slowly, often requiring 3-6 weeks before colonies appear
D: the antigen in the tuberculin skin test is a protein extracted from the organism
B
125
71: which one of the following statements most accurately depicts the ability of the organism to be cultured in the lab?
A: treponema pallidum from a chancre can be grown on a special artifical medium supplemented with cholesterol
B: mycobacterium leprae can be grown in the armadillo and the mouse footpad but not on any artificial media
C: mycobacterium TB can be grown on enriched artificial media and produces visible colonies in 48 to 96 hours
D: atypical mycobacteria are found widely in soil and water but cannot be cultured on artifical media in the lab
B
126
136: each of the following statements concerning M. leprae is correct except:
A: in lepromatous leprosy, large numbers of organisms are usually seen in acid-fast stained smears
B: the organism will grow on bacteriologic media in 3-6 weeks
C: prolonged therapy (9 months or longer) in required to prevent recurrence
D: loss of sensation due to nerve damage is often seen in leprosy
B
127
A: mycobacterium aviumintracellulare
B: treponema pallidum
C: rickettsia prowazekii
D: mycoplasma pneumoniae
138: is found primarily in the soil
A
128
A: mycobacterium aviumintracellulare
B: treponema pallidum
C: rickettsia prowazekii
D: mycoplasma pneumoniae
140: is an acid fast rod
A
129
CCQ 4:
your patient is a 5 yo man who is coughing up greenish blood-streaked sputum. for the past 2 weeks he has had fever and night sweats. he thinks he has lost about 10 lb. on physical exam, there are crackles in the apex of the right lung, and a chest xray shows a cavity in that location
of the following, which one is the least likely finding?
A: gram stain of the sputum shows no predominant organism
B: culture of the sputum on blood agar shows no predominant organism
C: culture of the sputum on lowenstein-jensen medium shows tan colonies after incubation for 4 weeks
D: rapid plasma reagin test reveals the causative organism
D
130
CCQ 34
your patient is a 40 yo man with a depigmented lesion on his chest that appeared about a month ago. the skin of the lesion is thickend and has lost sensation. he has lived most of his life in rural louisiana.
of the following tests, which one is the most appropriate to do to reveal the cause of this disease?
A: perform a biopsy of the lesion and do an acid-fast stain
B: culture on sabouraud's agar and look for germ tubes
C: culture on blood agar anaerobically and do a gram stain
D: obtain serum for a weil felix agglutination test
A
131
mycobacterium Tb (MTB) and mycobacterium avium-complex (MAC) are important causes of disease, esp. in immunocompromised patients. regarding these, which one of the following statements is the most accurate?
A: cell mediated immunity is the most important host defense mechanism against MTB, whereas antibody mediated immunity is the most important host defense mechanism against MAC?
B: in the clinical lab, MAC can be distinguished from MTB by the fact that MAC forms colonies in 7 days whereas MTB does not
C: multidrug resistant strains of MAC are much less common than of MTB
D: MAC is found in the enviornment and is not transmitted from person to person, whereas MTB is found in humans and is transmitted person to person
D
132
members of the genus mycobacterium stain better with acid fast stain than with the gram stain. which one of the following is the best explaination for this finding?
A: they lac a cell wall; therefore they cannot absorb the crystal violet
B: they have a thin cell wall that does not retain the crystal violet
C: they have a thick polysaccharide capsule that prevents entry of the iodine solution
D: they have a large amount of lipid in their cell wall that prevents entry of the crystal violet
D
