Methicillin-resistant Staphylococcus aureus (MRSA) resistance to all beta-lactam antibiotics is conferred by which specific molecular mechanism?

• A Production of extended-spectrum beta-lactamase (ESBL) encoded by blaZ gene
• B Overexpression of efflux pumps expelling beta-lactams from the bacterial cell
• C Mutation in penicillin-binding protein PBP1 reducing drug binding affinity
• D Acquisition of mecA gene encoding PBP2a (PBP2') with low affinity for beta-lactams ✓

Explanation

MRSA resistance is mediated by the mecA gene (located on mobile genetic element SCCmec), which encodes an altered penicillin-binding protein — PBP2a (also called PBP2'). PBP2a has very low affinity for all beta-lactam antibiotics (penicillins, cephalosporins, carbapenems), meaning cell wall synthesis can proceed even in the presence of these drugs. This pan-beta-lactam resistance distinguishes MRSA from penicillinase-producing MSSA strains (which produce beta-lactamase encoded by blaZ). Treatment of serious MRSA infections requires vancomycin, linezolid, daptomycin, or teicoplanin; trimethoprim-sulfamethoxazole is used for community MRSA skin infections.

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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