LATEST PATHOLOGY - MEDICAL
MICROBIOLOGY CERTIFICATION EXAM
OFFERED BY AMERICAN BOARD OF
PATHOLOGY (ABMS) | COMPLETE EXAM Q&A
WITH RATIONALES
1. A 45-year-old man with a history of intravenous
drug use presents with fever, back pain, and a new
heart murmur. Blood cultures grow small, gram-
positive cocci in pairs and chains that are catalase-
negative and optochin-resistant. The organism is bile-
esculin positive and grows in 6.5% NaCl broth. What
is the most likely organism?
A) Streptococcus pneumoniae
B) Enterococcus faecalis
C) Viridans group streptococcus
D) Staphylococcus aureus
Correct answer: B
Rationale: Enterococcus faecalis is catalase-
negative, gram-positive coccus in pairs/chains, bile-
esculin positive, and grows in 6.5% NaCl. Optochin-
resistant (pneumococcus is optochin-sensitive). IV
drug use predisposes to endocarditis.
,2. A 25-year-old woman presents with watery
diarrhea, abdominal cramps, and nausea after eating
fried rice from a restaurant. Symptoms began 4 hours
after the meal and resolved within 24 hours. What is
the most likely causative agent?
A) Bacillus cereus (emetic type)
B) Staphylococcus aureus
C) Clostridium perfringens
D) Salmonella enteritidis
Correct answer: A
Rationale: Bacillus cereus emetic toxin (cereulide)
causes rapid onset (1-6 hours) of nausea, vomiting,
and diarrhea, often associated with fried rice. Staph
aureus (B) also causes rapid vomiting but typically
from dairy or meat.
3. A 55-year-old man with chronic obstructive
pulmonary disease (COPD) develops pneumonia.
Sputum culture grows a gram-negative coccobacillus
that is oxidase-positive, produces a fruity odor
(grape-like), and is mucoid (hyaluronic acid capsule).
What is the most likely organism?
A) Haemophilus influenzae
B) Pseudomonas aeruginosa
,C) Klebsiella pneumoniae
D) Escherichia coli
Correct answer: B
Rationale: Pseudomonas aeruginosa is oxidase-
positive, produces a grape-like odor, and can be
mucoid (especially in cystic fibrosis). It is a common
cause of healthcare-associated pneumonia in COPD.
4. A 32-year-old man who is a farmer presents with a
non-healing ulcer on his forearm. The ulcer has a
raised, undermined border and is painless. Darkfield
microscopy of the exudate shows spirochetes. The
organism cannot be cultured on artificial media. What
is the most likely diagnosis?
A) Treponema pallidum (primary syphilis)
B) Treponema pertenue (yaws)
C) Borrelia burgdorferi (Lyme disease)
D) Leptospira interrogans
Correct answer: A
Rationale: Treponema pallidum is visualized by
darkfield microscopy, cannot be cultured on artificial
media, and causes primary chancre (painless ulcer
with raised, indurated border). Farmer (occupational
exposure not relevant here).
, 5. A 28-year-old woman presents with dysuria and
urinary frequency. Urinalysis shows positive nitrites
and leukocyte esterase. Urine culture grows
>100,000 CFU/mL of a gram-negative rod that is
lactose-fermenting, indole-positive, and produces a
green metallic sheen on EMB agar. What is the most
likely organism?
A) Klebsiella pneumoniae
B) Escherichia coli
C) Proteus mirabilis
D) Enterobacter cloacae
Correct answer: B
Rationale: E. coli is the most common cause of UTI. It
is lactose-fermenting, indole-positive, and produces
a green metallic sheen on EMB (eosin-methylene
blue) agar. Klebsiella (A) is lactose-fermenting but
indole-negative.
6. A 60-year-old man with a history of gastrectomy
presents with megaloblastic anemia and neurologic
symptoms. He recalls eating raw fish. Stool studies
show a broad tapeworm. What is the most likely
organism?
A) Taenia saginata (beef tapeworm)
MICROBIOLOGY CERTIFICATION EXAM
OFFERED BY AMERICAN BOARD OF
PATHOLOGY (ABMS) | COMPLETE EXAM Q&A
WITH RATIONALES
1. A 45-year-old man with a history of intravenous
drug use presents with fever, back pain, and a new
heart murmur. Blood cultures grow small, gram-
positive cocci in pairs and chains that are catalase-
negative and optochin-resistant. The organism is bile-
esculin positive and grows in 6.5% NaCl broth. What
is the most likely organism?
A) Streptococcus pneumoniae
B) Enterococcus faecalis
C) Viridans group streptococcus
D) Staphylococcus aureus
Correct answer: B
Rationale: Enterococcus faecalis is catalase-
negative, gram-positive coccus in pairs/chains, bile-
esculin positive, and grows in 6.5% NaCl. Optochin-
resistant (pneumococcus is optochin-sensitive). IV
drug use predisposes to endocarditis.
,2. A 25-year-old woman presents with watery
diarrhea, abdominal cramps, and nausea after eating
fried rice from a restaurant. Symptoms began 4 hours
after the meal and resolved within 24 hours. What is
the most likely causative agent?
A) Bacillus cereus (emetic type)
B) Staphylococcus aureus
C) Clostridium perfringens
D) Salmonella enteritidis
Correct answer: A
Rationale: Bacillus cereus emetic toxin (cereulide)
causes rapid onset (1-6 hours) of nausea, vomiting,
and diarrhea, often associated with fried rice. Staph
aureus (B) also causes rapid vomiting but typically
from dairy or meat.
3. A 55-year-old man with chronic obstructive
pulmonary disease (COPD) develops pneumonia.
Sputum culture grows a gram-negative coccobacillus
that is oxidase-positive, produces a fruity odor
(grape-like), and is mucoid (hyaluronic acid capsule).
What is the most likely organism?
A) Haemophilus influenzae
B) Pseudomonas aeruginosa
,C) Klebsiella pneumoniae
D) Escherichia coli
Correct answer: B
Rationale: Pseudomonas aeruginosa is oxidase-
positive, produces a grape-like odor, and can be
mucoid (especially in cystic fibrosis). It is a common
cause of healthcare-associated pneumonia in COPD.
4. A 32-year-old man who is a farmer presents with a
non-healing ulcer on his forearm. The ulcer has a
raised, undermined border and is painless. Darkfield
microscopy of the exudate shows spirochetes. The
organism cannot be cultured on artificial media. What
is the most likely diagnosis?
A) Treponema pallidum (primary syphilis)
B) Treponema pertenue (yaws)
C) Borrelia burgdorferi (Lyme disease)
D) Leptospira interrogans
Correct answer: A
Rationale: Treponema pallidum is visualized by
darkfield microscopy, cannot be cultured on artificial
media, and causes primary chancre (painless ulcer
with raised, indurated border). Farmer (occupational
exposure not relevant here).
, 5. A 28-year-old woman presents with dysuria and
urinary frequency. Urinalysis shows positive nitrites
and leukocyte esterase. Urine culture grows
>100,000 CFU/mL of a gram-negative rod that is
lactose-fermenting, indole-positive, and produces a
green metallic sheen on EMB agar. What is the most
likely organism?
A) Klebsiella pneumoniae
B) Escherichia coli
C) Proteus mirabilis
D) Enterobacter cloacae
Correct answer: B
Rationale: E. coli is the most common cause of UTI. It
is lactose-fermenting, indole-positive, and produces
a green metallic sheen on EMB (eosin-methylene
blue) agar. Klebsiella (A) is lactose-fermenting but
indole-negative.
6. A 60-year-old man with a history of gastrectomy
presents with megaloblastic anemia and neurologic
symptoms. He recalls eating raw fish. Stool studies
show a broad tapeworm. What is the most likely
organism?
A) Taenia saginata (beef tapeworm)
