title: Analysis of mechanisms involved in reduced susceptibility to ciprofloxacin in Salmonella enterica serotypes Typhi and Paratyphi A isolates from travellers to Southeast Asia.
abstract: Owing to multidrug resistance, quinolones and third-generation cephalosporins are currently used as key antibiotics to combat Salmonella organisms. Therapy failure due to reduced ciprofloxacin susceptibility has been reported in endemic areas, but also in imported disease. Different bacterial resistance mechanisms may result in reduced ciprofloxacin susceptibility. In this study, the presence and expression of different resistance mechanisms resulting in reduced minimum inhibitory concentrations (MICs) for ciprofloxacin were evaluated in 23 blood-culture-derived Salmonella enterica serotypes Typhi and Paratyphi A organisms from ill-returned travellers to Asia. The presence of mutations in the quinolone resistance-determining region (QRDR) of the gyrA gene as well as an activated efflux pump and plasmid-mediated quinolone resistance genes was determined. Resistance selection during therapy and the clonal relatedness of all isolates were established. Efflux pump inhibition did not appear to affect the MICs of ciprofloxacin and activity of the efflux pump appeared to be specific for nalidixic acid. Repeated exposure of the isolates to ciprofloxacin did not result in a significant increase in the MICs for ciprofloxacin. Repetitive sequence-based polymerase chain reaction (rep-PCR) profiles identified five different genotypes, but no correlation with resistance was observed. However, a significant relation was found with geographic region; reduced ciprofloxacin susceptibility was only found in travellers returning from India and Pakistan. All isolates with reduced ciprofloxacin susceptibility had a mutation at position 83 in the QRDR region of the gyrA gene. Plasmid-mediated quinolone resistance was not found. These findings confirm that the reduced ciprofloxacin MIC in S. Typhi and S. Paratyphi A is solely due to an amino acid substitution in the QRDR 'cluster' of the gyrA gene.
authors.affiliation: Department of Medical Microbiology and Infectious Diseases, Erasmus University Medical Center Rotterdam, Rotterdam, The Netherlands.
authors.forename: Robert-Jan
authors.initials: RJ
authors.lastname: Hassing
authors.forename: Godfred A
authors.initials: GA
authors.lastname: Menezes
authors.forename: Wilfred
authors.initials: W
authors.lastname: van Pelt
authors.forename: Pieter L
authors.initials: PL
authors.lastname: Petit
authors.forename: Perry J
authors.initials: PJ
authors.lastname: van Genderen
authors.forename: Wil H F
authors.initials: WH
authors.lastname: Goessens
mesh_terms: D019943:Amino Acid Substitution / Q000187:drug effects; D000900:Anti-Bacterial Agents / Q000494:pharmacology* / Q000627:therapeutic use; D001210:Asia, Southeastern; D001769:Blood / Q000382:microbiology; D002939:Ciprofloxacin / Q000494:pharmacology* / Q000627:therapeutic use; D027081:DNA Gyrase / Q000235:genetics; D024881:Drug Resistance, Bacterial; D005838:Genotype; D006801:Humans; D008826:Microbial Sensitivity Tests; D009268:Nalidixic Acid / Q000494:pharmacology / Q000627:therapeutic use; D010284:Paratyphoid Fever / Q000382:microbiology; D010957:Plasmids / Q000187:drug effects / Q000235:genetics; D016133:Polymerase Chain Reaction; D015363:Quinolones / Q000494:pharmacology / Q000627:therapeutic use; D012482:Salmonella paratyphi A / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D012485:Salmonella typhi / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification; D014195:Travel; D014435:Typhoid Fever / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D015363:Quinolones; D009268:Nalidixic Acid; D002939:Ciprofloxacin; D027081:DNA Gyrase