Plasmid-mediated quinolone resistance in Enterobacterales is most often mediated by qnr genes. What is the mechanism by which Qnr proteins protect the organism?

• A They reduce outer membrane porin expression to limit drug entry
• B They enzymatically acetylate and inactivate fluoroquinolones
• C They increase drug efflux through AcrAB-TolC pumps
• D They bind and protect DNA gyrase and topoisomerase IV from quinolone inhibition ✓

Explanation

Qnr proteins belong to the pentapeptide repeat family and act as protective decoys, binding directly to DNA gyrase and topoisomerase IV so that fluoroquinolones cannot form the lethal drug-enzyme-DNA cleaved complex. They typically cause low-level resistance that facilitates selection of higher-level chromosomal mutants. Fluoroquinolone-inactivating enzymes such as AAC(6')-Ib-cr exist separately, and efflux upregulation or porin loss are chromosomal, not plasmid-borne qnr effects.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.