Mechanisms of Resistance in Nontyphoidal Salmonella enterica Strains Exhibiting a Nonclassical Quinolone Resistance Phenotype

摘要: Nontyphoidal Salmonella enterica strains with a nonclassical quinolone resistance phenotype were isolated from patients returning Thailand or Malaysia to Finland. A total of 10 isolates seven serovars studied in detail, all which had reduced susceptibility (MIC ≥ 0.125 μg/ml) ciprofloxacin but either susceptible showed only low-level ≤ 32 nalidixic acid. Phenotypic characterization included testing by the agar dilution method and investigation efflux activity. Genotypic screening mutations resistance-determining regions (QRDR) gyrA, gyrB, parC, parE PCR denaturing high-pressure liquid chromatography amplification plasmid-mediated (PMQR) genes qnrA, qnrB, qnrS, qnrD, aac(6′)-Ib-cr, qepA PCR. PMQR was confirmed plasmid analysis, Southern hybridization, transfer. No QRDRs detected exception Thr57-Ser substitution within ParC seen S. serovar Typhimurium strains. The qnrA qnrS determinants detected. Plasmids carrying qnr alleles transferable vitro, reproducible Escherichia coli DH5α transformants. These data demonstrate emergence highly mobile genotype that, absence mutation topoisomerase genes, confers nontypical isolates. mechanism enables bacteria survive elevated concentrations, therefore, may be able expand during fluoroquinolone treatment. This is concern since mediated therefore mobilizable.