A blood culture isolate is identified as MRSA. The mechanism of methicillin resistance is:
- A Acquisition of mecA gene encoding PBP2a (penicillin-binding protein 2a) with very low affinity for all beta-lactam antibiotics ✓
- B Production of penicillinase (TEM beta-lactamase) hydrolyzing the beta-lactam ring
- C Efflux pump overexpression reducing intracellular methicillin concentration
- D Modification of porin channels preventing methicillin entry
Correct answer: A. Acquisition of mecA gene encoding PBP2a (penicillin-binding protein 2a) with very low affinity for all beta-lactam antibiotics
Explanation
MRSA resistance is mediated by the mecA gene (located on staphylococcal cassette chromosome mec, SCCmec) encoding PBP2a, a modified penicillin-binding protein with markedly reduced affinity for all beta-lactam antibiotics; this confers cross-resistance to all penicillins, cephalosporins, and carbapenems. Beta-lactamase hydrolysis mediates ordinary penicillin resistance (not methicillin resistance). Efflux pumps and porin changes are mechanisms seen in gram-negative bacteria.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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