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Microbiology BOC
Proper media for culture of a urethral discharge from a man include:
a sheep blood and phenylethyl alcohol agars b eosin-methylene blue and sheep blood
agars
c thioglycollate broth and chocolate agar
d chocolate and modified Thayer-Martin agars - ANSWER-d chocolate and modified
Thayer-Martin agars
d Chocolate agar and chocolate agar- based selective media should be used for
recovery of Neisseria gonorrhoeae from urethral discharge. Chocolate agar provides the
nutrients required by N gonorrhoeae and selective media contains antimicrobial agents
that inhibits other organisms and permits recovery of pathogenic Neisseria.
A sheep blood agar plate inoculated with 0.001mL of urine grows 70 colonies of
Staphylococcus aureus. How many colony forming units per mL of urine be reported?
a 70
b 700
c 7,000
d 70,000 - ANSWER-d 70,000
d When 0.001 mL of urine is plated, the growth of one colony is equivalent to 1000
CFU/mL. Thus 70 colonies is 70,000 CFU/mL.
The lowest concentration of antibiotic that inhibits growth of a test that inhibits growth of
a test organism is the:
a minimum inhibitory concentration
b serum inhibitory concentration
c minimum bactericidal titer
d maximum inhibitory titer - ANSWER-a minimum inhibitory concentration
a The MIC is a basic laboratory measurement of the activity of an antibiotic against an
organism. It is the lowest concentration of antibiotic that inhibits visible growth of the
organism. It does not represent the concentration of antibiotic that is lethal to the
organism.
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Which of the following clean catch urine culture colony counts indicates the patient likely
has a urinary tract infection?
a 10^1 CFU/mL
b 10^3 CFU/mL
c 10^5 CFU/mL
d no growth - ANSWER-b 10^3 CFU/mL
b Patients with infection often have at least 100,000 bacteria/mL of urine in the bladder.
However one third of young women with symptomatic cystitis have less than 100,000
bacteria/mL of urine. The Infectious Disease Society of America consensus definition of
cystitis is greater than or equal to 1,000 CFU/mL of a uropathogen.
The steam autoclave method of sterilization:
a uses 15 lbs of pressure for 15 minutes
b utilizes dry heat for 20 minutes
c produces a maximum temperature of 100 C
d requires a source of ethylene oxide - ANSWER-a uses 15 lbs of pressure for 15
minutes
a The traditional gravity displacement steam sterilization cycle is 121°C for 15 minutes
at 15 pounds per square inch. Ethylene oxide is an alternative sterilization method.
The expected colony count in a suprapubic urine from a healthy individual is:
a 0 CFU/mL
b 100 CFU/mL
c 1,000 CFU/mL
d 100,000 CFU/mL - ANSWER-a 0 CFU/mL
a Urine in the bladder is normally sterile. Suprapubic aspiration removes urine directly
from the bladder and yields a specimen free of urethral contamination.
An aspirate of a deep wound was plated on blood agar plates and incubated aerobically
and anaerobically. At 24 hours there was growth on both plates. This indicates that the
organism is
a(n):
a nonfermenter
b obligate anaerobe
c aerobe
d facultative anaerobe - ANSWER-d facultative anaerobe
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d Facultative anaerobes are organisms that can grow under both aerobic and anaerobic
conditions.
The proper blood-to-broth ratio for blood cultures to reduce the antibacterial effect of
serum in adults is:
a 1:2
b 1:3
c 1:10
d 1:30 - ANSWER-c 1:10
c Human blood contains substances that may inhibit microbial growth. Diluting blood in
culture broth reduces the concentration of these substances as well as any antibiotics
that may be present. The recommended blood broth ratio is 1:5-1:10. Dilutions less than
this may cause the blood to clot trapping organisms in the clot. Greater dilutions may
increase the time to detection
A penicillin-resistant Neisseria gonorrhoeae produces:
a alpha-hemolysin
b beta-lactamase
c enterotoxin
d coagulase - ANSWER-b beta-lactamase
b Antimicrobial resistance in Neisseria gonorrhoeae is widespread. The production of
beta-lactamase (penicillinase) breaks open the beta lactam ring of penicillin, destroying
its activity. Thus, Ngonorrhoeae that produce beta lactamase are resistant to penicillin.
Which selective medium is used for the isolation of gram-positive microorganisms?
a Columbia CNA with 5% sheep blood
b trypticase soy agar with 5% sheep blood
c eosin methylene blue
d modified Thayer-Martin - ANSWER-a Columbia CNA with 5% sheep blood
a Columbia CNA agar contains colistin and nalidixic acid, which inhibit most
gram-negative organisms. Eosin methylene blue is selective and inhibits gram-positive
organisms and modified Thayer Martin is selective and inhibits gram-positive
organisms, gram-negative bacilli and yeast.
The most sensitive substrate for the detection of beta-lactamases is:
a penicillin
b ampicillin
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c cefoxitin
d nitrocefin - ANSWER-d nitrocefin
d The chromogenic cephalosporin test using nitrocefin is the most sensitive and specific
test for detection of beta lactamase. Acidimetric tests employing penicillin are less
expensive, but not as sensitive, as the nitrocefin assay.
A Staphilococcus aureus isolate has an MIC of 4ug/m: to axacillin. There is uncertainty
as to whether this represents an oxacillin (heteroresistant) resistant strain or a
hyperproducer of beta-lactamase.
Strain Oxacillin Amoxicillin-clavulanic acid
strand A Sus Sus
stand B Sus Res
strand C Res Sus
strand D Res Res
Based on the above results for oxacillin and amoxicillin, which strand is
heteroresistant?
a strand A
b strand B
c strand C
d strand D - ANSWER-d strand D
d A Staphylococcus aureus isolate with an MIC of 4 pg/mL is resistant to oxacillin.. As
per the Clinical and Laboratory Standards Institute (CLSI) recommendations a
heteroresistant strain would be defined as a methicillin (oxacillin) resistant S aureus
(MRSA/ORSA). An MRSA/ORSA isolate would be reported as resistant to all beta
lactam agents, beta lactam/beta lactamase inhibitor combinations, such as amoxicillin-
clavulanic acid, and carbapenems.
13 An Enterococcus isolated from multiple blood cultures in a patient endocarditis
should be:
a screened for high level aminoglycoside resistance
b checked for tolerance
c assayed for serum antimicrobial activity
d tested for beta-lactamase production - ANSWER-a screened for high level
aminoglycoside resistance
a Systemic enterococcal infections, such as endocarditis, are commonly treated with a
cell-wall-active agent and an aminoglycoside.
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Microbiology BOC
Proper media for culture of a urethral discharge from a man include:
a sheep blood and phenylethyl alcohol agars b eosin-methylene blue and sheep blood
agars
c thioglycollate broth and chocolate agar
d chocolate and modified Thayer-Martin agars - ANSWER-d chocolate and modified
Thayer-Martin agars
d Chocolate agar and chocolate agar- based selective media should be used for
recovery of Neisseria gonorrhoeae from urethral discharge. Chocolate agar provides the
nutrients required by N gonorrhoeae and selective media contains antimicrobial agents
that inhibits other organisms and permits recovery of pathogenic Neisseria.
A sheep blood agar plate inoculated with 0.001mL of urine grows 70 colonies of
Staphylococcus aureus. How many colony forming units per mL of urine be reported?
a 70
b 700
c 7,000
d 70,000 - ANSWER-d 70,000
d When 0.001 mL of urine is plated, the growth of one colony is equivalent to 1000
CFU/mL. Thus 70 colonies is 70,000 CFU/mL.
The lowest concentration of antibiotic that inhibits growth of a test that inhibits growth of
a test organism is the:
a minimum inhibitory concentration
b serum inhibitory concentration
c minimum bactericidal titer
d maximum inhibitory titer - ANSWER-a minimum inhibitory concentration
a The MIC is a basic laboratory measurement of the activity of an antibiotic against an
organism. It is the lowest concentration of antibiotic that inhibits visible growth of the
organism. It does not represent the concentration of antibiotic that is lethal to the
organism.
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Which of the following clean catch urine culture colony counts indicates the patient likely
has a urinary tract infection?
a 10^1 CFU/mL
b 10^3 CFU/mL
c 10^5 CFU/mL
d no growth - ANSWER-b 10^3 CFU/mL
b Patients with infection often have at least 100,000 bacteria/mL of urine in the bladder.
However one third of young women with symptomatic cystitis have less than 100,000
bacteria/mL of urine. The Infectious Disease Society of America consensus definition of
cystitis is greater than or equal to 1,000 CFU/mL of a uropathogen.
The steam autoclave method of sterilization:
a uses 15 lbs of pressure for 15 minutes
b utilizes dry heat for 20 minutes
c produces a maximum temperature of 100 C
d requires a source of ethylene oxide - ANSWER-a uses 15 lbs of pressure for 15
minutes
a The traditional gravity displacement steam sterilization cycle is 121°C for 15 minutes
at 15 pounds per square inch. Ethylene oxide is an alternative sterilization method.
The expected colony count in a suprapubic urine from a healthy individual is:
a 0 CFU/mL
b 100 CFU/mL
c 1,000 CFU/mL
d 100,000 CFU/mL - ANSWER-a 0 CFU/mL
a Urine in the bladder is normally sterile. Suprapubic aspiration removes urine directly
from the bladder and yields a specimen free of urethral contamination.
An aspirate of a deep wound was plated on blood agar plates and incubated aerobically
and anaerobically. At 24 hours there was growth on both plates. This indicates that the
organism is
a(n):
a nonfermenter
b obligate anaerobe
c aerobe
d facultative anaerobe - ANSWER-d facultative anaerobe
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d Facultative anaerobes are organisms that can grow under both aerobic and anaerobic
conditions.
The proper blood-to-broth ratio for blood cultures to reduce the antibacterial effect of
serum in adults is:
a 1:2
b 1:3
c 1:10
d 1:30 - ANSWER-c 1:10
c Human blood contains substances that may inhibit microbial growth. Diluting blood in
culture broth reduces the concentration of these substances as well as any antibiotics
that may be present. The recommended blood broth ratio is 1:5-1:10. Dilutions less than
this may cause the blood to clot trapping organisms in the clot. Greater dilutions may
increase the time to detection
A penicillin-resistant Neisseria gonorrhoeae produces:
a alpha-hemolysin
b beta-lactamase
c enterotoxin
d coagulase - ANSWER-b beta-lactamase
b Antimicrobial resistance in Neisseria gonorrhoeae is widespread. The production of
beta-lactamase (penicillinase) breaks open the beta lactam ring of penicillin, destroying
its activity. Thus, Ngonorrhoeae that produce beta lactamase are resistant to penicillin.
Which selective medium is used for the isolation of gram-positive microorganisms?
a Columbia CNA with 5% sheep blood
b trypticase soy agar with 5% sheep blood
c eosin methylene blue
d modified Thayer-Martin - ANSWER-a Columbia CNA with 5% sheep blood
a Columbia CNA agar contains colistin and nalidixic acid, which inhibit most
gram-negative organisms. Eosin methylene blue is selective and inhibits gram-positive
organisms and modified Thayer Martin is selective and inhibits gram-positive
organisms, gram-negative bacilli and yeast.
The most sensitive substrate for the detection of beta-lactamases is:
a penicillin
b ampicillin
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c cefoxitin
d nitrocefin - ANSWER-d nitrocefin
d The chromogenic cephalosporin test using nitrocefin is the most sensitive and specific
test for detection of beta lactamase. Acidimetric tests employing penicillin are less
expensive, but not as sensitive, as the nitrocefin assay.
A Staphilococcus aureus isolate has an MIC of 4ug/m: to axacillin. There is uncertainty
as to whether this represents an oxacillin (heteroresistant) resistant strain or a
hyperproducer of beta-lactamase.
Strain Oxacillin Amoxicillin-clavulanic acid
strand A Sus Sus
stand B Sus Res
strand C Res Sus
strand D Res Res
Based on the above results for oxacillin and amoxicillin, which strand is
heteroresistant?
a strand A
b strand B
c strand C
d strand D - ANSWER-d strand D
d A Staphylococcus aureus isolate with an MIC of 4 pg/mL is resistant to oxacillin.. As
per the Clinical and Laboratory Standards Institute (CLSI) recommendations a
heteroresistant strain would be defined as a methicillin (oxacillin) resistant S aureus
(MRSA/ORSA). An MRSA/ORSA isolate would be reported as resistant to all beta
lactam agents, beta lactam/beta lactamase inhibitor combinations, such as amoxicillin-
clavulanic acid, and carbapenems.
13 An Enterococcus isolated from multiple blood cultures in a patient endocarditis
should be:
a screened for high level aminoglycoside resistance
b checked for tolerance
c assayed for serum antimicrobial activity
d tested for beta-lactamase production - ANSWER-a screened for high level
aminoglycoside resistance
a Systemic enterococcal infections, such as endocarditis, are commonly treated with a
cell-wall-active agent and an aminoglycoside.
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