Which virulence factor of Staphylococcus aureus enables it to evade phagocytosis by binding the Fc portion of IgG at the wrong end, thereby preventing opsonisation?
- A Coagulase
- B Protein A ✓
- C Catalase
- D Hyaluronidase
Correct answer: B. Protein A
Explanation
Protein A is a surface component of the S. aureus cell wall that binds the Fc region of IgG1, IgG2 and IgG4, leaving the Fab regions facing outward. This reverses opsonisation and blocks complement activation via the classical pathway. Coagulase promotes fibrin clot formation but does not bind antibody, making it the most tempting distractor.
Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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