Methicillin-resistant Staphylococcus aureus (MRSA) resistance to all beta-lactam antibiotics is mediated by expression of a modified penicillin-binding protein. What is the specific genetic element responsible for this resistance?

• A mecA gene (carried on SCCmec cassette) encoding PBP2a with low affinity for beta-lactams ✓
• B blaZ gene encoding a beta-lactamase enzyme that hydrolyzes methicillin
• C vanA gene cluster altering peptidoglycan terminus to D-Ala-D-Lac
• D pbpB gene encoding PBP2b with intrinsically reduced affinity

Explanation

mecA, located on the mobile staphylococcal cassette chromosome mec (SCCmec), encodes PBP2a (also called PBP2'), a penicillin-binding protein with markedly reduced affinity for all beta-lactam antibiotics. Since PBP2a can continue cell-wall synthesis when other PBPs are inhibited, MRSA is resistant to all beta-lactams including carbapenems. blaZ encodes a conventional beta-lactamase that does not confer methicillin resistance; vanA is the basis for VRSA/VRE resistance.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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