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 - correct 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 - correct 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 - correct 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.
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 - correct 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 - correct 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 - correct 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 - correct answer ✔d facultative anaerobe
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 - correct 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 - correct 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 - correct answer ✔a Columbia CNA with 5% sheep
blood
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 - correct 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 - correct 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 - correct 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.
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 - correct 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 - correct 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 - correct 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 - correct answer ✔d facultative anaerobe
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 - correct 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 - correct 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 - correct answer ✔a Columbia CNA with 5% sheep
blood
