title: Molecular study of quinolone resistance mechanisms and clonal relationship of Salmonella enterica clinical isolates.
abstract: In the last few years, the number of Salmonella enterica strains resistant to nalidixic acid has steadily increased. In a previous study, the quinolone susceptibility phenotype and genotype of 38 S. enterica clinical isolates (19 S. enterica serovar Typhimurium and 19 S. enterica serovar Enteritidis) were determined. Forty-two percent of the isolates showed nalidixic acid resistance associated with a mutation in gyrA together with putative overexpression of efflux pump(s). In this study, mutations in the quinolone resistance-determining region (QRDR) of parE and the regulators of AcrAB (acrR, marRAB, soxRS and ramR) were analysed. Intracellular accumulation of ciprofloxacin and nalidixic acid was determined. Gene expression of the efflux pump components acrB, tolC, acrF and emrB was also assessed. In addition, an epidemiological study of the isolates by multilocus sequence typing (MLST) and pulsed-field gel electrophoresis (PFGE) was performed. No mutations were detected in parE, whereas two amino acid substitutions were found in two susceptible strains in MarR (I84L) and AcrR (N214T) in one strain each, although both were suggested to be polymorphisms. No changes in the gene expression of acrB, tolC, acrF and emrB were detected between nalidixic-acid-resistant and -susceptible strains. Intracellular accumulation was not useful to reveal differences. Epidemiological analysis showed an important clonal relatedness among the S. Enteritidis isolates, whereas major divergence was seen for S. Typhimurium. Altogether, these results suggest the presence of previously undiscovered drug efflux pump(s) and confirm the high clonality of S. Enteritidis and the genetic divergence of S. Typhimurium.
authors.affiliation: Centre for International Health Research, CRESIB, Hospital Clínic, University of Barcelona, Rosselló 149-153, 1st Floor, 08036 Barcelona, Spain.
authors.forename: Clara
authors.initials: C
authors.lastname: Ballesté-Delpierre
authors.affiliation: Centre for International Health Research, CRESIB, Hospital Clínic, University of Barcelona, Rosselló 149-153, 1st Floor, 08036 Barcelona, Spain.
authors.forename: Mar
authors.initials: M
authors.lastname: Solé
authors.affiliation: Department of Physical Chemistry, School of Pharmacy, University of Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain.
authors.forename: Òscar
authors.initials: Ò
authors.lastname: Domènech
authors.affiliation: Department of Physical Chemistry, School of Pharmacy, University of Barcelona, Martí i Franquès 1, 08028 Barcelona, Spain.
authors.forename: Jordi
authors.initials: J
authors.lastname: Borrell
authors.affiliation: Centre for International Health Research, CRESIB, Hospital Clínic, University of Barcelona, Rosselló 149-153, 1st Floor, 08036 Barcelona, Spain; Department of Microbiology, Hospital Clínic, School of Medicine, University of Barcelona, Villarroel 170, 08036 Barcelona, Spain. Electronic address: jvila@ub.edu.
authors.forename: Jordi
authors.initials: J
authors.lastname: Vila
authors.affiliation: Centre for International Health Research, CRESIB, Hospital Clínic, University of Barcelona, Rosselló 149-153, 1st Floor, 08036 Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Fàbrega
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000235:genetics; D024881:Drug Resistance, Bacterial; D016521:Electrophoresis, Gel, Pulsed-Field; D020869:Gene Expression Profiling; D005838:Genotype; D006801:Humans; D058885:Multilocus Sequence Typing; D009154:Mutation; D015363:Quinolones / Q000494:pharmacology*; D012480:Salmonella Infections / Q000382:microbiology*; D019779:Salmonella enterica / Q000145:classification* / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D015363:Quinolones
keywords: Efflux pumps; MLST; PFGE; Quinolone resistance; Salmonella