Plasmid-mediated quinolone resistance mediated by the qnr gene differs from classical chromosomal fluoroquinolone resistance in that it:
- A Encodes a pentapeptide-repeat protein that protects DNA gyrase and topoisomerase IV from drug binding, producing low-level resistance ✓
- B Encodes an efflux pump belonging to the major facilitator superfamily
- C Alters the lipopolysaccharide so that the drug cannot penetrate the outer membrane
- D Hydrolyses the piperazinyl ring of ciprofloxacin enzymatically before drug entry
Correct answer: A. Encodes a pentapeptide-repeat protein that protects DNA gyrase and topoisomerase IV from drug binding, producing low-level resistance
Explanation
Qnr proteins are pentapeptide-repeat proteins that bind directly to the gyrase and topoisomerase IV holoenzymes and shield them from quinolone attachment, conferring low-level resistance that facilitates selection of higher-level mutants. Classical high-level resistance arises instead from chromosomal point mutations in the QRDR of gyrA and parC, often combined with efflux. Qnr does not pump drugs out, alter permeability, or degrade the drug; no bacterial enzyme that destroys fluoroquinolones has been described, which removes option D outright.
Reference: Ananthanarayan and Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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