title: Evaluation of colistin susceptibility in multidrug-resistant clinical isolates from cystic fibrosis, France.
abstract: The emergence of multidrug-resistant (MDR) bacteria in cystic fibrosis (CF) patients has led to the use of colistin drug and the emergence of colistin-resistant Gram-negative bacteria. The aim of this study was to compare the disk diffusion and Etest methods for colistin susceptibility testing on MDR bacteria associated with CF from Marseille, France. Forty-nine MDR clinical isolates (27 Stenotrophomonas maltophilia, 22 Achromobacter xylosoxidans) were used in this study. Disk diffusion and Etest assays were used to assess the reliability of these two techniques. For S. maltophilia, 25 out of 27 isolates had low minimum inhibitory concentrations (MICs, 0.125-0.75 mg/L), whereas two isolates displayed high MICs (32 mg/L). Similarly, 19 out of 22 A. xylosoxidans isolates had low MICs (0.75-3.0 mg/L), whereas three isolates had high MICs (32-256 mg/L). The diameters of zone inhibition with a 50-μg colistin disk displayed a good correlation with the MICs obtained by the Etest. Susceptible and resistant strains were eventually separated using a disk diffusion assay at a cut-off of ≤ 12 mm for a 50-μg disk. Colistin displayed excellent activity against S. maltophilia and A. xylosoxidans and the disk diffusion assay could be confidently used to determine the susceptibility to colistin for MDR Gram-negative bacteria in the context of CF.
authors.affiliation: URMITE CNRS-IRD, UMR 6236, Méditerranée Infection, Faculté de Médecine et de Pharmacie, Aix-Marseille Université, 27 Boulevard Jean Moulin, 13385, Marseille Cedex 05, France.
authors.forename: S
authors.initials: S
authors.lastname: Biswas
authors.forename: J-C
authors.initials: JC
authors.lastname: Dubus
authors.forename: M
authors.initials: M
authors.lastname: Reynaud-Gaubert
authors.forename: N
authors.initials: N
authors.lastname: Stremler
authors.forename: J-M
authors.initials: JM
authors.lastname: Rolain
mesh_terms: D042441:Achromobacter denitrificans / Q000187:drug effects* / Q000302:isolation & purification; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D003550:Cystic Fibrosis / Q000150:complications*; D024901:Drug Resistance, Multiple, Bacterial; D005602:France; D016905:Gram-Negative Bacterial Infections / Q000382:microbiology*; D006801:Humans; D008826:Microbial Sensitivity Tests; D020615:Stenotrophomonas maltophilia / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D003091:Colistin