title: In vitro selection of fluoroquinolone resistance in Brucella melitensis.
abstract: Moxifloxacin-resistant mutants of Brucella melitensis 16M [moxifloxacin minimum inhibitory concentration (MIC)=1mg/L] were selected in order to characterise fluoroquinolone resistance mechanisms in this species. Eight independent mutants were obtained, with moxifloxacin MICs of 16-32mg/L. The mutants displayed variable cross-resistance levels to other fluoroquinolone compounds, but no increased resistance to aminoglycosides, tetracycline, rifampicin, macrolides or co-trimoxazole. Sequencing of type II topoisomerase-encoding genes (gyrA, gyrB, parC and parE), which are natural targets for fluoroquinolones, revealed a gyrA mutation leading to the amino acid substitution Ala83Val (Escherichia coli numbering system) in five mutants with a moxifloxacin MIC of 32mg/L, whereas no mutation was found in the remaining three mutants with a MIC of 16mg/L. Phenylalanine-arginine-beta-naphthylamide dihydrochloride, an efflux pump inhibitor, reduced moxifloxacin MICs by a factor of two to eight in all resistant mutants. In B. melitensis, fluoroquinolone resistance may arise from gyrA mutation and efflux pump overexpression mechanisms.
authors.affiliation: Laboratoire de Bactériologie, Centre Hospitalier Universitaire de Grenoble, Université Joseph Fourier, BP217, 38043 Grenoble Cedex 9, France.
authors.forename: N
authors.initials: N
authors.lastname: Ravanel
authors.forename: B
authors.initials: B
authors.lastname: Gestin
authors.forename: M
authors.initials: M
authors.lastname: Maurin
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D017347:Brucella melitensis / Q000187:drug effects*; D004252:DNA Mutational Analysis; D026942:DNA Topoisomerases / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004791:Enzyme Inhibitors / Q000494:pharmacology; D024841:Fluoroquinolones / Q000494:pharmacology*; D026901:Membrane Transport Proteins / Q000378:metabolism; D008826:Microbial Sensitivity Tests; D020125:Mutation, Missense
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004791:Enzyme Inhibitors; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins; D026942:DNA Topoisomerases