QnrA

qnrA is a gene that encodes a pentapeptide repeat protein which provides plasmid-mediated resistance to quinolone antibiotics in bacteria. It is part of the qnr gene family, which also includes qnrB, qnrS, qnrC, and qnrD. Among these, qnrA was one of the first plasmid-borne quinolone resistance determinants identified in clinical isolates of Enterobacterales.

qnrA is typically located on transferable plasmids and is frequently found alongside other resistance genes, such as beta-lactamases. It has been detected in a range of Gram-negative bacteria, including Escherichia coli, Klebsiella pneumoniae, and Enterobacter species. The distribution of qnrA varies by geographic region and over time due to differences in antibiotic usage and plasmid circulation.

The mechanism of resistance involves QnrA proteins binding to DNA gyrase and topoisomerase IV, protecting these target enzymes from fluoroquinolones. This protection reduces drug binding and results in a modest increase in the minimum inhibitory concentration. By itself, qnrA typically causes low-level resistance; however, it can facilitate the emergence of higher-level resistance when combined with chromosomal mutations or additional PMQR determinants.

Detection and monitoring of qnrA rely on molecular methods such as PCR assays specific for qnrA and sequencing. In research settings, plasmid profiling and conjugation experiments help confirm plasmid localization. Clinically, the presence of qnrA underscores the potential for rapid spread of resistance and the importance of prudent antibiotic use and surveillance.