Beta-lactam antibiotics act by binding PBPs (penicillin-binding proteins). In MRSA, which specific mechanism confers resistance to ALL beta-lactams including carbapenems?

• A Overproduction of beta-lactamase enzymes that hydrolyze all beta-lactam rings
• B Acquisition of mecA gene encoding PBP2a (PBP2'), a modified PBP with very low affinity for beta-lactams ✓
• C Efflux pumps of the RND family that export all beta-lactam antibiotics
• D Reduced outer membrane permeability secondary to OprD porin loss

Explanation

mecA is a mobile genetic element encoding PBP2a (also called PBP2'), an alternative penicillin-binding protein with extremely low affinity for all beta-lactam antibiotics. PBP2a can still catalyze peptidoglycan cross-linking even when native PBPs are blocked, conferring pan-beta-lactam resistance. Beta-lactamase overproduction (option A) and efflux pumps (C) confer resistance to some beta-lactams but not carbapenems in S. aureus; OprD porin loss (D) is the carbapenem resistance mechanism in Pseudomonas.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.