qnrmediated

Qnrmediated quinolone resistance refers to resistance conferred by qnr genes carried on plasmids that reduce the activity of quinolones and fluoroquinolones. The qnr gene family encodes pentapeptide repeat proteins that interact with DNA gyrase and topoisomerase IV, protecting these targets from drug binding and thereby diminishing drug efficacy.

Mechanistically, Qnr proteins act as protective shields for the enzymes rather than directly inactivating the drug. This often results in low-level resistance, with minimum inhibitory concentrations increasing modestly, typically a few-fold. However, this low-level resistance can promote the selection of higher-level resistance when combined with additional mechanisms.

Genetically, qnr determinants are frequently plasmid-borne and located on mobile genetic elements that facilitate horizontal transfer between bacteria. In many settings, qnrA, qnrB, and qnrS are the most commonly reported, while qnrC, qnrD, and qnrVC have also been identified in various species and environments. qnr genes are often found alongside other PMQR determinants such as the qepA efflux pump and the aac(6')-Ib-cr enzyme, and can coexist with chromosomal mutations in gyrA and parC that further elevate resistance.

Clinical and epidemiological significance varies by context but is globally reported in Enterobacterales and other Gram-negative bacteria from clinical, animal, and environmental sources. Although qnr-mediated resistance alone may not always cause treatment failure, it facilitates the emergence and spread of higher-level quinolone resistance, complicating therapy.

Detection typically relies on molecular methods (PCR and sequencing) and phenotypic susceptibility testing. Management emphasizes antibiotic stewardship, infection control, and monitoring of PMQR determinants to limit dissemination.