A nasal swab from a healthcare worker screens positive for MRSA. The isolate is confirmed by a cefoxitin disk diffusion (zone ≤21 mm). Which gene encodes the altered penicillin-binding protein responsible for methicillin resistance in Staphylococcus aureus?
- A blaZ gene on a plasmid
- B vanA gene on Tn1546 transposon
- C mecA gene on staphylococcal cassette chromosome mec (SCCmec) ✓
- D cfr gene on a conjugative plasmid
Correct answer: C. mecA gene on staphylococcal cassette chromosome mec (SCCmec)
Explanation
mecA encodes PBP2a (also called PBP2'), a penicillin-binding protein with very low affinity for all beta-lactams, and is located on the mobile genetic element SCCmec. blaZ encodes beta-lactamase responsible for penicillin (not methicillin) resistance. vanA confers vancomycin resistance in enterococci and rare VRSA. cfr encodes a methyltransferase causing linezolid/chloramphenicol resistance.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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