title: AcrAB-TolC directs efflux-mediated multidrug resistance in Salmonella enterica serovar typhimurium DT104.
abstract: Multidrug-resistant Salmonella enterica serovar Typhimurium definitive phage type 104 (DT104) strains harbor a genomic island, called Salmonella genomic island 1 (SGI1), which contains an antibiotic resistance gene cluster conferring resistance to ampicillin, chloramphenicol, florfenicol, streptomycin, sulfonamides, and tetracyclines. They may be additionally resistant to quinolones. Among the antibiotic resistance genes there are two, i.e., floR and tet(G), which code for efflux pumps of the major facilitator superfamily with 12 transmembrane segments that confer resistance to chloramphenicol-florfenicol and the tetracyclines, respectively. In the present study we determined, by constructing acrB and tolC mutants, the role of the AcrAB-TolC multidrug efflux system in the multidrug resistance of several DT104 strains displaying additional quinolone resistance or not displaying quinolone resistance. This study shows that the quinolone resistance and the decreased fluoroquinolone susceptibilities of the strains are highly dependent on the AcrAB-TolC efflux system and that single mutations in the quinolone resistance-determining region of gyrA are of little relevance in mediating this resistance. Overproduction of the AcrAB efflux pump, as determined by Western blotting with an anti-AcrA polyclonal antibody, appeared to be the major mechanism of resistance to quinolones. Moreover, chloramphenicol-florfenicol and tetracycline resistance also appeared to be highly dependent on the presence of AcrAB-TolC, since the introduction of mutations in the respective acrB and tolC genes resulted in a susceptible or intermediate resistance phenotype, according to clinical MIC breakpoints, despite the presence of the FloR and Tet(G) efflux pumps. Resistance to other antibiotics, ampicillin, streptomycin, and sulfonamides, was not affected in the acrB and tolC mutants of DT104 strains harboring SGI1. Therefore, AcrAB-TolC appears to direct efflux-mediated resistance to quinolones, chloramphenicol-florfenicol, and tetracyclines in multidrug-resistant S. enterica serovar Typhimurium DT104 strains.
authors.affiliation: Unité BioAgresseurs, Santé et Environnement, Institut National de la Recherche Agronomique, 37380 Nouzilly, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Baucheron
authors.forename: Shaun
authors.initials: S
authors.lastname: Tyler
authors.forename: David
authors.initials: D
authors.lastname: Boyd
authors.forename: Michael R
authors.initials: MR
authors.lastname: Mulvey
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Chaslus-Dancla
authors.forename: Axel
authors.initials: A
authors.lastname: Cloeckaert
mesh_terms: D001426:Bacterial Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D015153:Blotting, Western; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D005798:Genes, Bacterial / Q000235:genetics; D009154:Mutation / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism
chemical_list: C493251:AcrAB-TolC protein, Salmonella enterica; D001426:Bacterial Proteins; D002352:Carrier Proteins