BOC MICROBIOLOGY 2025 EXAM
QUESTIONS WITH CORRECT
ANSWERS (ALREADY PASSED)
An anaerobic, spore-forming, nonmotile, gram-positive bacillus isolated from a foot
wound is most likely:
Actinomyces israelii
Clostridium perfringens
Bacillus subtilis
Eubacterium lentum - Answer-Clostridium perfringens
The reverse CAMP test, lecithinase production, double zone hemolysis, and Gram stain
morphology are all useful criteria in the identification of:
Clostridium perfringens
Streptococcus agalactiae
Propionibacterium acnes
Bacillus anthracis - Answer-Clostridium perfringens
An anaerobic gram-positive bacilli with subterminal spores was isolated from a
peritoneal abscess. The most likely identification of this organism is:
Bacillus cereus
Clostridium septicum
Eubacterium lentum
Bifidobacterium dentium - Answer-Clostridium septicum
The most meaningful laboratory procedure in confirming the diagnosis of clinical
botulism is:
Demonstration of toxin in the patients serum
Recovery of Clostridium botulinum from suspected food
Recovery of Clostridium botulinum from the patients stool
Gram stain of suspected food for gram-positive, sporulating bacilli - Answer-
Demonstration of toxin in the patients serum
,A stool sample is sent to the laboratory for culture to rule out Clostridium difficile. What
media should the microbiologist use and what is the appearnace of the organisms on
this media?
BBE: colonies turn black
Brucella agar: red pigmented colonies
CCFA: yellow, ground glass colonies
CNA: double zone hemolytic colonies - Answer-CCFA: yellow, ground glass colonies
A Gram stain of a nectrotic wound specimen showed large gram-positive bacilli. There
was 3+ growth on anaerobic media only, with colonies producing a double zone of
hemolysis. To identify the organism, the microbiologist should:
Determine if the organism ferments glucose
Perform the oxidase test
Set up egg yolk agar plate
Test for bile tolerance - Answer-Set up egg yolk agar plate
Which of the following genera include anaerobic gram-negative nonsporulating bacilli?
Brucella
Pasteurella
Actinomyces
Bacteroides - Answer-Bacteroides
A control stain of Clostridium should be used an anaerobe jar to assure:
That plate media is working
That an anaerobic environment is achieved
That the jar is filled with a sufficient number of plates
That the indicator strip is checked - Answer-That an anaerobic environment is achieved
A sputum specimen from a patient with a known Klebsiella pneumoniae infection is
received in the laboratory for fungus culture. The proper procedure for handling this
specimen is to:
Reject the current specimen and request a repeat culture when the bacterial organism
is no longer present
Incubate culture tubes at room temperature in order to inhibit the bacterial organism
Include media that have cycloheximide and chloramphenicol added to inhibit bacterial
organisms and saprophytic fungi
Perform a direct PAS stain; if no fungal organisms are seen, reject the specimen -
Answer-Include media that have cycloheximide and chloramphenicol added to inhibit
bacterial organisms and saprophytic fungi
,Lab workers should always work under a biological safety hood when working with
cultures of:
Streptococcus pyogenes
Staphylococcus aureus
Candida albicans
Coccidioides immitis - Answer-Coccidioides immitis
The appropriate specimen for the diagnosis of mucormycosis is:
Nasal swab
Sputum
Sinus washing
Eschar biopsy - Answer-Eschar biopsy
A sputum specimen received at 8 am for an AFB smear reveals acid-fast bacilli. An
additional sputum is submitted that afternoon. This specimen was concentrated by the
NALC-sodium hydroxide method and inoculated on 2 Lowenstein-Jensen slants and
held for 8 weeks at 35°C in 5-10% CO₂. No growth occurs. The best explanation is that:
The hypochlorite technique was not used
An improper specimen was submitted for culture
Improper media was used for culture
Cultures were held for an insufficient period of time - Answer-An improper specimen
was submitted for culture
The preferred carbon source for mycobacteria is:
Glycerol
Glucose
Fatty acids
Casein hydrolysate - Answer-Glycerol
A first morning sputum is received for culture of mycobacteria. It is digested and
concentrated by the N-acetyl-L-cysteine alkali method. Two Lowenstein-Jensen slants
are incubated in the dark at 35°C with 5-10% CO₂. The smears reveal acid-fast bacilli,
and after 7 days no growth appears on the slants. The best explanation is:
Improper specimen submitted
Incorrect concentration procedure
Exposure to CO₂ prevents growth
Cultures held for insufficient length of time - Answer-Cultures held for insufficient length
of time
A first morning sputum specimen is received for acid-fast culture. The specimen is
centrifuged, and the sediment is inoculated on 2 Lowenstein-Jensen slants, which are
, incubated at 35°C in 5-10% CO₂. After 1 week, the slants show abundant growth over
the entire surface. Stains reveal gram-negative bacilli. To avoid this problem:
Utilize a medium that inhibits bacterial growth
Add sodium hypochlorite to the sediment before inoculation
Incubate the tubes at room temperature to retard bacterial growth
Decontaminate the specimen with sodium hydroxide - Answer-Decontaminate the
specimen with sodium hydroxide
A first morning sputum is received for culture of acid-fast bacilli. It is digested and
concentrated by the N-acetyl-L-cysteine alkali method. Two Sabouraud dextrose slants
are incubated in the dark at 35°C with 5-10% CO₂. The smears reveal acid-fast bacilli,
but the slants show no growth after 8 weeks. The explanation is:
Improper media used
Incorrect concetration procedure used
Improper specimen submitted
Exposure to CO₂ prevents growth - Answer-Improper media used
Which of the following combinations of media provides an egg base, agar base, and a
selective egg or agar base media?
Lowenstein-Jensen, American Throacic Society (ATS), Middelbrook 7H11
Lowenstein-Jensen, Middlebrook 7H11, Lowenstein-Jensen Gruft
Middlebrook 7H10, Petragnani, Lowenstein-Jensen
Middlebrook 7H10, Middlebrook 7H11, Mitchison 7H11 - Answer-Lowenstein-Jensen,
Middlebrook 7H11, Lowenstein-Jensen Gruft
The function of N-acetyl-L-cysteine is the reagent for acid-fast digestion-
decontamination procedure is to:
Inhibit growth of normal respiratory flora
Inhibit growth of fungi
Neutralize the sodium hydroxide
Liquefy the mucus - Answer-Liquefy the mucus
Which of the following reagents should be used as a mucolytic, alkaline reagent for
digestion and decontamination of a sputum for mycobacterial culture?
N-acetyl-L-cystine and NaOH
NaOH alone
Zephiran-trisodium phosphate
Oxalic acid - Answer-N-acetyl-L-cystine and NaOH
When staining acid-fast bacilli with Truant auramine-rhodamine stain, potassium
permanganate is used as a:
QUESTIONS WITH CORRECT
ANSWERS (ALREADY PASSED)
An anaerobic, spore-forming, nonmotile, gram-positive bacillus isolated from a foot
wound is most likely:
Actinomyces israelii
Clostridium perfringens
Bacillus subtilis
Eubacterium lentum - Answer-Clostridium perfringens
The reverse CAMP test, lecithinase production, double zone hemolysis, and Gram stain
morphology are all useful criteria in the identification of:
Clostridium perfringens
Streptococcus agalactiae
Propionibacterium acnes
Bacillus anthracis - Answer-Clostridium perfringens
An anaerobic gram-positive bacilli with subterminal spores was isolated from a
peritoneal abscess. The most likely identification of this organism is:
Bacillus cereus
Clostridium septicum
Eubacterium lentum
Bifidobacterium dentium - Answer-Clostridium septicum
The most meaningful laboratory procedure in confirming the diagnosis of clinical
botulism is:
Demonstration of toxin in the patients serum
Recovery of Clostridium botulinum from suspected food
Recovery of Clostridium botulinum from the patients stool
Gram stain of suspected food for gram-positive, sporulating bacilli - Answer-
Demonstration of toxin in the patients serum
,A stool sample is sent to the laboratory for culture to rule out Clostridium difficile. What
media should the microbiologist use and what is the appearnace of the organisms on
this media?
BBE: colonies turn black
Brucella agar: red pigmented colonies
CCFA: yellow, ground glass colonies
CNA: double zone hemolytic colonies - Answer-CCFA: yellow, ground glass colonies
A Gram stain of a nectrotic wound specimen showed large gram-positive bacilli. There
was 3+ growth on anaerobic media only, with colonies producing a double zone of
hemolysis. To identify the organism, the microbiologist should:
Determine if the organism ferments glucose
Perform the oxidase test
Set up egg yolk agar plate
Test for bile tolerance - Answer-Set up egg yolk agar plate
Which of the following genera include anaerobic gram-negative nonsporulating bacilli?
Brucella
Pasteurella
Actinomyces
Bacteroides - Answer-Bacteroides
A control stain of Clostridium should be used an anaerobe jar to assure:
That plate media is working
That an anaerobic environment is achieved
That the jar is filled with a sufficient number of plates
That the indicator strip is checked - Answer-That an anaerobic environment is achieved
A sputum specimen from a patient with a known Klebsiella pneumoniae infection is
received in the laboratory for fungus culture. The proper procedure for handling this
specimen is to:
Reject the current specimen and request a repeat culture when the bacterial organism
is no longer present
Incubate culture tubes at room temperature in order to inhibit the bacterial organism
Include media that have cycloheximide and chloramphenicol added to inhibit bacterial
organisms and saprophytic fungi
Perform a direct PAS stain; if no fungal organisms are seen, reject the specimen -
Answer-Include media that have cycloheximide and chloramphenicol added to inhibit
bacterial organisms and saprophytic fungi
,Lab workers should always work under a biological safety hood when working with
cultures of:
Streptococcus pyogenes
Staphylococcus aureus
Candida albicans
Coccidioides immitis - Answer-Coccidioides immitis
The appropriate specimen for the diagnosis of mucormycosis is:
Nasal swab
Sputum
Sinus washing
Eschar biopsy - Answer-Eschar biopsy
A sputum specimen received at 8 am for an AFB smear reveals acid-fast bacilli. An
additional sputum is submitted that afternoon. This specimen was concentrated by the
NALC-sodium hydroxide method and inoculated on 2 Lowenstein-Jensen slants and
held for 8 weeks at 35°C in 5-10% CO₂. No growth occurs. The best explanation is that:
The hypochlorite technique was not used
An improper specimen was submitted for culture
Improper media was used for culture
Cultures were held for an insufficient period of time - Answer-An improper specimen
was submitted for culture
The preferred carbon source for mycobacteria is:
Glycerol
Glucose
Fatty acids
Casein hydrolysate - Answer-Glycerol
A first morning sputum is received for culture of mycobacteria. It is digested and
concentrated by the N-acetyl-L-cysteine alkali method. Two Lowenstein-Jensen slants
are incubated in the dark at 35°C with 5-10% CO₂. The smears reveal acid-fast bacilli,
and after 7 days no growth appears on the slants. The best explanation is:
Improper specimen submitted
Incorrect concentration procedure
Exposure to CO₂ prevents growth
Cultures held for insufficient length of time - Answer-Cultures held for insufficient length
of time
A first morning sputum specimen is received for acid-fast culture. The specimen is
centrifuged, and the sediment is inoculated on 2 Lowenstein-Jensen slants, which are
, incubated at 35°C in 5-10% CO₂. After 1 week, the slants show abundant growth over
the entire surface. Stains reveal gram-negative bacilli. To avoid this problem:
Utilize a medium that inhibits bacterial growth
Add sodium hypochlorite to the sediment before inoculation
Incubate the tubes at room temperature to retard bacterial growth
Decontaminate the specimen with sodium hydroxide - Answer-Decontaminate the
specimen with sodium hydroxide
A first morning sputum is received for culture of acid-fast bacilli. It is digested and
concentrated by the N-acetyl-L-cysteine alkali method. Two Sabouraud dextrose slants
are incubated in the dark at 35°C with 5-10% CO₂. The smears reveal acid-fast bacilli,
but the slants show no growth after 8 weeks. The explanation is:
Improper media used
Incorrect concetration procedure used
Improper specimen submitted
Exposure to CO₂ prevents growth - Answer-Improper media used
Which of the following combinations of media provides an egg base, agar base, and a
selective egg or agar base media?
Lowenstein-Jensen, American Throacic Society (ATS), Middelbrook 7H11
Lowenstein-Jensen, Middlebrook 7H11, Lowenstein-Jensen Gruft
Middlebrook 7H10, Petragnani, Lowenstein-Jensen
Middlebrook 7H10, Middlebrook 7H11, Mitchison 7H11 - Answer-Lowenstein-Jensen,
Middlebrook 7H11, Lowenstein-Jensen Gruft
The function of N-acetyl-L-cysteine is the reagent for acid-fast digestion-
decontamination procedure is to:
Inhibit growth of normal respiratory flora
Inhibit growth of fungi
Neutralize the sodium hydroxide
Liquefy the mucus - Answer-Liquefy the mucus
Which of the following reagents should be used as a mucolytic, alkaline reagent for
digestion and decontamination of a sputum for mycobacterial culture?
N-acetyl-L-cystine and NaOH
NaOH alone
Zephiran-trisodium phosphate
Oxalic acid - Answer-N-acetyl-L-cystine and NaOH
When staining acid-fast bacilli with Truant auramine-rhodamine stain, potassium
permanganate is used as a:
