FPGEE Microbiology and Immunology Flashcards

Which component of the complement system forms the membrane attack complex (MAC)?

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.

Vancomycin is the drug of choice for serious infections caused by MRSA because it:

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.

Which hepatitis virus is transmitted via the fecal-oral route and does NOT cause chronic infection?

Answer: Hepatitis A

Hepatitis A virus (HAV) is transmitted via contaminated food/water (fecal-oral) and causes only acute, self-limiting infection without chronicity.

The CD4+ T helper cell count in an HIV-positive patient below which prophylaxis for Pneumocystis jirovecii pneumonia (PCP) is initiated is:

Answer: < 200 cells/µL

PCP prophylaxis with trimethoprim-sulfamethoxazole is initiated when the CD4+ count falls below 200 cells/µL.

Which antifungal mechanism is unique to the echinocandin class (e.g., caspofungin)?

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.

Clostridium difficile causes antibiotic-associated colitis primarily through production of:

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.