Bacteria: Structure and Pathogenesis · USMLE Step 1

Which bacterial structure is most commonly associated with resistance to phagocytosis and enhanced virulence?

  1. Flagellum
  2. Pilus
  3. Capsule
  4. Ribosome
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Correct answer: Capsule

Capsules are polysaccharide (or sometimes polypeptide) layers external to the cell wall that hinder phagocytosis. Many pathogenic bacteria use capsules to evade host immune defenses.

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