Bacteria: Structure and Pathogenesis · USMLE Step 1

A bacterium with a thin peptidoglycan layer and outer membrane is least likely to be killed by which host defense?

  1. Lysozyme
  2. Macrophage phagocytosis
  3. Antibody-mediated opsonization
  4. Complement membrane attack complex
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Correct answer: Lysozyme

Lysozyme primarily degrades peptidoglycan. Gram-negative bacteria have only a thin peptidoglycan and an outer membrane which reduces lysozyme access, conferring resistance.

Difficulty: Medium Question 13 of 17

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