FPGEE FPGEE Microbiology and Immunology 2 — Questions and Answers
Question 1: Which component of the complement system forms the membrane attack complex (MAC)?
- C1q
- C3b
- C5b-9 (Correct answer)
- C4b2a
Correct answer: C5b-9
The membrane attack complex consists of complement proteins C5b, C6, C7, C8, and multiple C9 molecules that create pores in bacterial membranes.
Question 2: Vancomycin is the drug of choice for serious infections caused by MRSA because it:
- Inhibits ribosomal 30S subunit
- Binds D-Ala-D-Ala of peptidoglycan precursors (Correct answer)
- Disrupts the cell membrane directly
- Inhibits DNA gyrase
Correct answer: Binds D-Ala-D-Ala of peptidoglycan precursors
Vancomycin binds to the D-Ala-D-Ala terminus of peptidoglycan precursors, preventing transglycosylation and cell wall synthesis without using PBPs.
Question 3: Which hepatitis virus is transmitted via the fecal-oral route and does NOT cause chronic infection?
- Hepatitis B
- Hepatitis C
- Hepatitis D
- Hepatitis A (Correct answer)
Correct answer: Hepatitis A
Hepatitis A virus (HAV) is transmitted via contaminated food/water (fecal-oral) and causes only acute, self-limiting infection without chronicity.
Question 4: The CD4+ T helper cell count in an HIV-positive patient below which prophylaxis for Pneumocystis jirovecii pneumonia (PCP) is initiated is:
- < 500 cells/µL
- < 350 cells/µL
- < 200 cells/µL (Correct answer)
- < 100 cells/µL
Correct answer: < 200 cells/µL
PCP prophylaxis with trimethoprim-sulfamethoxazole is initiated when the CD4+ count falls below 200 cells/µL.
Question 5: Which antifungal mechanism is unique to the echinocandin class (e.g., caspofungin)?
- Inhibition of ergosterol synthesis (14α-demethylase)
- Binding to ergosterol and disrupting membrane
- Inhibition of β-1,3-glucan synthase (Correct answer)
- Inhibition of thymidylate synthase
Correct answer: Inhibition of β-1,3-glucan synthase
Echinocandins inhibit β-1,3-glucan synthase, disrupting fungal cell wall synthesis, which has no human counterpart.
Question 6: Clostridium difficile causes antibiotic-associated colitis primarily through production of:
- Endotoxin (lipopolysaccharide)
- Exotoxins A and B (Correct answer)
- Protein A
- Leukotoxin
Correct answer: Exotoxins A and B
C. difficile produces toxin A (enterotoxin) and toxin B (cytotoxin), which disrupt colonic epithelial tight junctions and cause pseudomembranous colitis.
FPGEE FPGEE Microbiology and Immunology 2
Which component of the complement system forms the membrane attack complex (MAC)?