title: Role of efflux pumps and topoisomerase mutations in fluoroquinolone resistance in Campylobacter jejuni and Campylobacter coli.
abstract: Point mutations in the topoisomerase (DNA gyrase A) gene are known to be associated with fluoroquinolone resistance in Campylobacter. Recent studies have shown that an efflux pump encoded by cmeABC is also involved in decreased susceptibilities to fluoroquinolones, as well as other antimicrobials. Genome analysis suggests that Campylobacter jejuni contains at least nine other putative efflux pumps. Using insertional inactivation and site-directed mutagenesis, we investigated the potential contributions of these pumps to susceptibilities to chloramphenicol, ciprofloxacin, erythromycin, and tetracycline in C. jejuni and Campylobacter coli. Insertional inactivation of cmeB resulted in 4- to 256-fold decreases in the MICs of chloramphenicol, ciprofloxacin, erythromycin, and tetracycline, with erythromycin being the most significantly affected. In contrast, inactivation of all other putative efflux pumps had no effect on susceptibility to any of the four antimicrobials tested. Mutation of gyrA at codon 86 (Thr-Ile) caused 128- and 64-fold increases in the MICs of ciprofloxacin and nalidixic acid, respectively. The replacement of the mutated gyrA with a wild-type gyrA allele resulted in a 32-fold decrease in the ciprofloxacin MIC and no change in the nalidixic acid MIC. Our findings indicate that CmeABC is the only efflux pump among those tested that influences antimicrobial resistance in Campylobacter and that a point mutation (Thr-86-Ile) in gyrA directly causes fluoroquinolone resistance in Campylobacter. These two mechanisms work synergistically in acquiring and maintaining fluoroquinolone resistance in Campylobacter species.
authors.affiliation: Department of Nutrition and Food Science, 0112 Skinner Building, University of Maryland, College Park, MD 20742, USA.
authors.forename: Beilei
authors.initials: B
authors.lastname: Ge
authors.forename: Patrick F
authors.initials: PF
authors.lastname: McDermott
authors.forename: David G
authors.initials: DG
authors.lastname: White
authors.forename: Jianghong
authors.initials: J
authors.lastname: Meng
mesh_terms: D000890:Anti-Infective Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D017000:Campylobacter coli / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D016123:Campylobacter jejuni / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D027081:DNA Gyrase / Q000235:genetics* / Q000378:metabolism; D024881:Drug Resistance, Bacterial / Q000235:genetics*; D024841:Fluoroquinolones / Q000494:pharmacology; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D017422:Sequence Analysis, DNA
chemical_list: D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins; D027081:DNA Gyrase