qnrC

qnrC is a gene that encodes a member of the Qnr family of plasmid-mediated quinolone resistance determinants. Like other qnr genes, qnrC produces a pentapeptide repeat protein that protects bacterial DNA gyrase and topoisomerase IV from inhibition by fluoroquinolones, resulting in reduced susceptibility rather than high-level resistance on its own.

qnrC is typically carried on plasmids in Gram-negative bacteria, enabling horizontal transfer between strains and species. It has been detected in diverse Enterobacterales and other opportunistic pathogens, often on mobile genetic elements such as plasmids, sometimes alongside other antimicrobial resistance genes. The genetic context can include IncQ-type plasmids and other vectors that facilitate dissemination.

Clinical and epidemiological implications of qnrC include its contribution to low-level fluoroquinolone resistance, which can serve as a stepping stone for the selection of additional resistance through chromosomal mutations in gyrA, gyrB, parC, or parE. In practice, the presence of qnrC can complicate treatment decisions and may be associated with broader resistance profiles when co-occurring resistance determinants are present.

Detection of qnrC is typically achieved by molecular methods such as PCR followed by sequencing, or by comprehensive molecular resistance gene panels used in surveillance. Reports of qnrC emphasize the ongoing need for monitoring plasmid-mediated resistance as part of efforts to manage fluoroquinolone efficacy and antimicrobial stewardship.