Single or double mutational alterations of GyrA associated with fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli

We looked for the presence of gyrA mutations in seven fluoroquinolone-resis tant French clinical isolates of Campylobacter jejuni and Campylobacter col i. Three of the five isolates of C. jejuni and the two isolates of C coli h ad high-level resistance to nalidixic acid (MICs 128-256 mug/ml) and ciprof loxacin (MICs 32 mug/ml). A gyrA mutation was found in all these isolates l eading to the following substitutions: Thr86-Ile in four cases and Asp90-Ty r for one C. coli strain. One isolate had high-level resistance to nalidixi c acid (MIC 64 mug/ml) but low-level resistance to ciprofloxacin (MIC 2 mug /ml) and also carried a gyrA mutation leading to a Thr86-Ala substitution. The last isolate of C. jejuni studied displayed an atypical resistance phen otype: It was resistant to high levels of ciprofloxacin (MIC 64 mug/ml) but remained fully susceptible to nalidixic acid (MIC 2 mug/ml). This phenotyp e was not explained by, the presence of peculiar mutations in gyrA or gyrB. It carried a gyrA mutation leading to a Thr86-Ile substitution and was dev oid of gyrB mutation. Despite numerous attempts with various degenerate oli gonucleotide primers deduced from conserved regions of known parC genes, we were unable to amplify a corresponding sequence in C. jejuni or C. coli. F irst-step and second-step in vitro mutants, derived from reference strain C . coli ATCC 33559 with ciprofloxacin or moxifloxacin as selecting agents, w ere found to carry one and two mutations in gyrA, respectively. In contrast with the results obtained with clinical isolates, a variety of gyrA mutati ons were obtained in vitro.