M CERTIFICATION EXAM PREP 2026 Updated
Practice Questions Comprehensive Medical
Microbiology Review Detailed Explanations | Verified
Answers | Complete Success Workbook
Examination Content Areas and Weightings:
Content Area Percentage
Bacteriology 40 – 45%
Mycology 10 – 15%
Parasitology 10 – 15%
Virology 10 – 15%
Immunology/Serology 5 – 10%
Laboratory Operations 5 – 10%
SECTION 1: BACTERIOLOGY – GRAM-POSITIVE ORGANISMS
(Questions 1-20)
QUESTION 1:
A 65-year-old male with a history of COPD presents with fever, productive cough,
and chest pain. Sputum culture grows gram-positive cocci in pairs and chains,
alpha-hemolytic colonies on blood agar, and is optochin-sensitive. What is the
MOST likely organism?
,A) Streptococcus agalactiae
B) Streptococcus pyogenes
C) Streptococcus pneumoniae
D) Enterococcus faecalis
Answer: C) Streptococcus pneumoniae
Rationale: Streptococcus pneumoniae is a gram-positive, encapsulated
diplococcus (cocci in pairs) that is alpha-hemolytic on blood agar (greenish
discoloration). It is optochin-sensitive, bile-soluble, and is the most common cause
of community-acquired pneumonia, particularly in elderly patients and those with
underlying lung disease. S. agalactiae (A) is beta-hemolytic and bacitracin-
resistant. S. pyogenes (B) is beta-hemolytic and bacitracin-sensitive. Enterococcus
(D) is alpha-hemolytic or non-hemolytic but is optochin-resistant and grows in
6.5% NaCl.
QUESTION 2:
A wound culture from a patient with a diabetic foot ulcer grows gram-positive
cocci in clusters, catalase-positive, coagulase-positive, and produces yellow
colonies on mannitol salt agar. What is the MOST likely organism?
A) Staphylococcus epidermidis
B) Staphylococcus aureus
C) Staphylococcus saprophyticus
D) Micrococcus luteus
Answer: B) Staphylococcus aureus
Rationale: Staphylococcus aureus is a gram-positive coccus in clusters (grape-like
clusters) that is catalase-positive and coagulase-positive. It ferments mannitol,
producing yellow colonies on mannitol salt agar. It is a common cause of skin and
soft tissue infections, including diabetic foot ulcers. S. epidermidis (A) is
coagulase-negative. S. saprophyticus (C) is coagulase-negative and is associated
with urinary tract infections. Micrococcus (D) is catalase-positive but coagulase-
negative and produces yellow colonies on nutrient agar.
,QUESTION 3:
A throat culture from a child with pharyngitis grows beta-hemolytic colonies on
blood agar. The organism is gram-positive cocci in chains, catalase-negative, and
is inhibited by bacitracin. What is the MOST likely organism?
A) Streptococcus pyogenes
B) Streptococcus agalactiae
C) Streptococcus pneumoniae
D) Enterococcus faecalis
Answer: A) Streptococcus pyogenes
Rationale: Streptococcus pyogenes (Group A Streptococcus) is the classic cause
of bacterial pharyngitis ("strep throat"). It is a gram-positive coccus in chains, beta-
hemolytic on blood agar (clear zone of hemolysis), catalase-negative, and
bacitracin-sensitive (susceptible to bacitracin disk). S. agalactiae (B) is bacitracin-
resistant and is associated with neonatal infections. S. pneumoniae (C) is alpha-
hemolytic. Enterococcus (D) is not beta-hemolytic.
QUESTION 4:
Which of the following organisms is the MOST common cause of neonatal
meningitis and is characterized by gram-positive cocci in chains with a narrow
zone of beta-hemolysis?
A) Streptococcus pyogenes
B) Streptococcus agalactiae
C) Listeria monocytogenes
D) Escherichia coli
Answer: B) Streptococcus agalactiae
Rationale: Streptococcus agalactiae (Group B Streptococcus) is the most common
cause of neonatal meningitis and sepsis. It is a gram-positive coccus in chains with
a narrow zone of beta-hemolysis on blood agar (CAMP test-positive). It is
transmitted from the mother to the infant during delivery. E. coli (D) is the most
, common cause of neonatal meningitis in premature infants but is a gram-negative
bacillus. Listeria (C) is a gram-positive bacillus.
QUESTION 5:
A urine culture from a young female with symptoms of a urinary tract infection
grows gram-positive cocci in clusters, catalase-positive, coagulase-negative, and
resistant to novobiocin. What is the MOST likely organism?
A) Staphylococcus aureus
B) Staphylococcus epidermidis
C) Staphylococcus saprophyticus
D) Enterococcus faecalis
Answer: C) Staphylococcus saprophyticus
Rationale: Staphylococcus saprophyticus is a coagulase-negative staphylococcus
that is a common cause of urinary tract infections in young, sexually active
females. It is novobiocin-resistant (differentiating it from S. epidermidis, which is
novobiocin-sensitive). S. aureus (A) is coagulase-positive. S. epidermidis (B) is
novobiocin-sensitive and is more commonly associated with prosthetic device
infections. Enterococcus (D) is catalase-negative.
QUESTION 6:
A blood culture from a patient with endocarditis grows gram-positive cocci in pairs
and chains, alpha-hemolytic, optochin-resistant, and grows in 6.5% NaCl broth.
What is the MOST likely organism?
A) Streptococcus pneumoniae
B) Streptococcus viridans group
C) Enterococcus faecalis
D) Streptococcus agalactiae
Answer: C) Enterococcus faecalis
Practice Questions Comprehensive Medical
Microbiology Review Detailed Explanations | Verified
Answers | Complete Success Workbook
Examination Content Areas and Weightings:
Content Area Percentage
Bacteriology 40 – 45%
Mycology 10 – 15%
Parasitology 10 – 15%
Virology 10 – 15%
Immunology/Serology 5 – 10%
Laboratory Operations 5 – 10%
SECTION 1: BACTERIOLOGY – GRAM-POSITIVE ORGANISMS
(Questions 1-20)
QUESTION 1:
A 65-year-old male with a history of COPD presents with fever, productive cough,
and chest pain. Sputum culture grows gram-positive cocci in pairs and chains,
alpha-hemolytic colonies on blood agar, and is optochin-sensitive. What is the
MOST likely organism?
,A) Streptococcus agalactiae
B) Streptococcus pyogenes
C) Streptococcus pneumoniae
D) Enterococcus faecalis
Answer: C) Streptococcus pneumoniae
Rationale: Streptococcus pneumoniae is a gram-positive, encapsulated
diplococcus (cocci in pairs) that is alpha-hemolytic on blood agar (greenish
discoloration). It is optochin-sensitive, bile-soluble, and is the most common cause
of community-acquired pneumonia, particularly in elderly patients and those with
underlying lung disease. S. agalactiae (A) is beta-hemolytic and bacitracin-
resistant. S. pyogenes (B) is beta-hemolytic and bacitracin-sensitive. Enterococcus
(D) is alpha-hemolytic or non-hemolytic but is optochin-resistant and grows in
6.5% NaCl.
QUESTION 2:
A wound culture from a patient with a diabetic foot ulcer grows gram-positive
cocci in clusters, catalase-positive, coagulase-positive, and produces yellow
colonies on mannitol salt agar. What is the MOST likely organism?
A) Staphylococcus epidermidis
B) Staphylococcus aureus
C) Staphylococcus saprophyticus
D) Micrococcus luteus
Answer: B) Staphylococcus aureus
Rationale: Staphylococcus aureus is a gram-positive coccus in clusters (grape-like
clusters) that is catalase-positive and coagulase-positive. It ferments mannitol,
producing yellow colonies on mannitol salt agar. It is a common cause of skin and
soft tissue infections, including diabetic foot ulcers. S. epidermidis (A) is
coagulase-negative. S. saprophyticus (C) is coagulase-negative and is associated
with urinary tract infections. Micrococcus (D) is catalase-positive but coagulase-
negative and produces yellow colonies on nutrient agar.
,QUESTION 3:
A throat culture from a child with pharyngitis grows beta-hemolytic colonies on
blood agar. The organism is gram-positive cocci in chains, catalase-negative, and
is inhibited by bacitracin. What is the MOST likely organism?
A) Streptococcus pyogenes
B) Streptococcus agalactiae
C) Streptococcus pneumoniae
D) Enterococcus faecalis
Answer: A) Streptococcus pyogenes
Rationale: Streptococcus pyogenes (Group A Streptococcus) is the classic cause
of bacterial pharyngitis ("strep throat"). It is a gram-positive coccus in chains, beta-
hemolytic on blood agar (clear zone of hemolysis), catalase-negative, and
bacitracin-sensitive (susceptible to bacitracin disk). S. agalactiae (B) is bacitracin-
resistant and is associated with neonatal infections. S. pneumoniae (C) is alpha-
hemolytic. Enterococcus (D) is not beta-hemolytic.
QUESTION 4:
Which of the following organisms is the MOST common cause of neonatal
meningitis and is characterized by gram-positive cocci in chains with a narrow
zone of beta-hemolysis?
A) Streptococcus pyogenes
B) Streptococcus agalactiae
C) Listeria monocytogenes
D) Escherichia coli
Answer: B) Streptococcus agalactiae
Rationale: Streptococcus agalactiae (Group B Streptococcus) is the most common
cause of neonatal meningitis and sepsis. It is a gram-positive coccus in chains with
a narrow zone of beta-hemolysis on blood agar (CAMP test-positive). It is
transmitted from the mother to the infant during delivery. E. coli (D) is the most
, common cause of neonatal meningitis in premature infants but is a gram-negative
bacillus. Listeria (C) is a gram-positive bacillus.
QUESTION 5:
A urine culture from a young female with symptoms of a urinary tract infection
grows gram-positive cocci in clusters, catalase-positive, coagulase-negative, and
resistant to novobiocin. What is the MOST likely organism?
A) Staphylococcus aureus
B) Staphylococcus epidermidis
C) Staphylococcus saprophyticus
D) Enterococcus faecalis
Answer: C) Staphylococcus saprophyticus
Rationale: Staphylococcus saprophyticus is a coagulase-negative staphylococcus
that is a common cause of urinary tract infections in young, sexually active
females. It is novobiocin-resistant (differentiating it from S. epidermidis, which is
novobiocin-sensitive). S. aureus (A) is coagulase-positive. S. epidermidis (B) is
novobiocin-sensitive and is more commonly associated with prosthetic device
infections. Enterococcus (D) is catalase-negative.
QUESTION 6:
A blood culture from a patient with endocarditis grows gram-positive cocci in pairs
and chains, alpha-hemolytic, optochin-resistant, and grows in 6.5% NaCl broth.
What is the MOST likely organism?
A) Streptococcus pneumoniae
B) Streptococcus viridans group
C) Enterococcus faecalis
D) Streptococcus agalactiae
Answer: C) Enterococcus faecalis
