COMLEX Level 1 Microbiology Practice Set
Part 1 — Bacteriology (Q1–10)
Q1.
A 6-year-old boy presents with sore throat, fever, and tender cervical lymphadenopathy. His
throat appears erythematous with gray-white exudates. A throat swab grows Streptococcus
pyogenes. Which of the following virulence factors allows the organism to resist phagocytosis?
A. Streptolysin O
B. Hyaluronic acid capsule
C. M protein
D. Streptokinase
E. DNase
Answer: C. M protein
Explanation: S. pyogenes’ M protein inhibits complement activation and phagocytosis, a key
virulence factor in rheumatic fever.
OMM tie-in: Cervical chain lymphatics often congest; suboccipital release improves lymphatic
drainage and immune response.
Q2.
A 30-year-old IV drug user develops fever and a new systolic murmur. Blood cultures grow
Staphylococcus aureus. Which enzyme enables this organism to evade host defenses and form
abscesses?
A. Catalase
B. Coagulase
C. Hyaluronidase
D. Protein A
E. Lipase
Answer: B. Coagulase
Explanation: Coagulase converts fibrinogen to fibrin, coating bacteria to resist phagocytosis.
OMM link: Rib raising T1–T4 may normalize sympathetic tone to the heart during systemic
infection.
, Q3.
A 45-year-old man with a history of alcoholism presents with productive cough, “currant jelly”
sputum, and right upper lobe infiltrate. Which of the following organisms is most likely?
A. Klebsiella pneumoniae
B. Legionella pneumophila
C. Pseudomonas aeruginosa
D. Haemophilus influenzae
E. Mycoplasma pneumoniae
Answer: A. Klebsiella pneumoniae
Explanation: Causes lobar pneumonia with thick mucoid sputum due to polysaccharide capsule;
common in alcoholics and diabetics.
OMM: Rib raising for T1–T6 can aid pulmonary function by balancing autonomic tone.
Q4.
A 23-year-old college student presents with dysuria and purulent urethral discharge. Gram stain
shows Gram-negative diplococci inside neutrophils. Which mechanism allows this pathogen to
evade host immunity?
A. Capsule formation
B. Antigenic variation of pili
C. Endotoxin production
D. IgA protease secretion
E. Exotoxin A production
Answer: B. Antigenic variation of pili
Explanation: Neisseria gonorrhoeae frequently changes pilin genes, preventing long-term
immunity.
Q5.
A 58-year-old farmer develops a painless ulcer with a black eschar on his hand after handling
animal hides. Which organism is the most likely cause?
A. Bacillus anthracis
B. Clostridium perfringens
C. Yersinia pestis
D. Francisella tularensis
E. Brucella melitensis
Part 1 — Bacteriology (Q1–10)
Q1.
A 6-year-old boy presents with sore throat, fever, and tender cervical lymphadenopathy. His
throat appears erythematous with gray-white exudates. A throat swab grows Streptococcus
pyogenes. Which of the following virulence factors allows the organism to resist phagocytosis?
A. Streptolysin O
B. Hyaluronic acid capsule
C. M protein
D. Streptokinase
E. DNase
Answer: C. M protein
Explanation: S. pyogenes’ M protein inhibits complement activation and phagocytosis, a key
virulence factor in rheumatic fever.
OMM tie-in: Cervical chain lymphatics often congest; suboccipital release improves lymphatic
drainage and immune response.
Q2.
A 30-year-old IV drug user develops fever and a new systolic murmur. Blood cultures grow
Staphylococcus aureus. Which enzyme enables this organism to evade host defenses and form
abscesses?
A. Catalase
B. Coagulase
C. Hyaluronidase
D. Protein A
E. Lipase
Answer: B. Coagulase
Explanation: Coagulase converts fibrinogen to fibrin, coating bacteria to resist phagocytosis.
OMM link: Rib raising T1–T4 may normalize sympathetic tone to the heart during systemic
infection.
, Q3.
A 45-year-old man with a history of alcoholism presents with productive cough, “currant jelly”
sputum, and right upper lobe infiltrate. Which of the following organisms is most likely?
A. Klebsiella pneumoniae
B. Legionella pneumophila
C. Pseudomonas aeruginosa
D. Haemophilus influenzae
E. Mycoplasma pneumoniae
Answer: A. Klebsiella pneumoniae
Explanation: Causes lobar pneumonia with thick mucoid sputum due to polysaccharide capsule;
common in alcoholics and diabetics.
OMM: Rib raising for T1–T6 can aid pulmonary function by balancing autonomic tone.
Q4.
A 23-year-old college student presents with dysuria and purulent urethral discharge. Gram stain
shows Gram-negative diplococci inside neutrophils. Which mechanism allows this pathogen to
evade host immunity?
A. Capsule formation
B. Antigenic variation of pili
C. Endotoxin production
D. IgA protease secretion
E. Exotoxin A production
Answer: B. Antigenic variation of pili
Explanation: Neisseria gonorrhoeae frequently changes pilin genes, preventing long-term
immunity.
Q5.
A 58-year-old farmer develops a painless ulcer with a black eschar on his hand after handling
animal hides. Which organism is the most likely cause?
A. Bacillus anthracis
B. Clostridium perfringens
C. Yersinia pestis
D. Francisella tularensis
E. Brucella melitensis
