Alterations in thegyrA andparC Genes inSalmonellaspp. FollowingIn VitroExposure to Fluoroquinolones

Abstract

We characterize alterations in the QRDR fragment of gyrA and parC in Salmonella spp. following repeated exposure to different quinolones in two in vitro models. Mutations in QRDR of gyrA were found in only 25% of the mutants. The most frequent mutations were Asp87(R)Asn and Asp87(R)Tyr. Strains with the former mutation had a higher ciprofloxacin MIC than those with the latter. We did not find mutations in parC. Our data confirm that mutation in the QRDR fragment of gyrA is the mechanism that produces the greatest decrease in fluoroquinolone susceptibility. There is a greater reduction in the ciprofloxacin susceptibility of strains that were originally nalidixic acid-resistant than in that of strains that were originally susceptible, and this confirms that there is a greater likelihood of therapeutic failures with such strains.

Genotypic Diversity of Ciprofloxacin Nonsusceptibility and Its Relationship with Minimum Inhibitory Concentrations in Nontyphoidal Salmonella Clinical Isolates in Taiwan

“…QRDR mutations in gyrA (82.1%) were more frequently observed than those in parC (59%) or parE (20.5%) in our 39 CIP-nonsusceptible NTS human isolates, and concurrent double mutations in both gyrA and parC coexisted in 18 strains (50%) highly resistant to CIP (Table 2). After in vitro exposure to FQs, compared with parC, gyrA was more inclined to undergo mutation in Salmonella spp., with the most frequent mutations observed in Asp87Asn and Asp87Tyr [23]. In addition, the predominance of gyrA with a rare report of gyrB was observed in other studies; however, the prevalence of parC and parE varied in human CIP-nonsusceptible NTS isolates.…”