Mechanisms of resistance in non-typhoidal Salmonella enterica exhibiting a novel quinolone resistance phenotype

Abstract number: P1536

Caddick J.M., Lindgren M., Webber M.A., Kotilainen P., Siitonen A., Hakanen A.J., Piddock L.J.V.

Objective: To determine the mechanisms which underpin a novel quinolone resistance phenotype of Salmonella enterica isolates from Finnish patients. All isolates were susceptible to nalidixic acid but had reduced susceptibility to ciprofloxacin.

Methods: Six Salmonella enterica isolates, consisting of five serovars (Corvallis, Stanley, Mbandaka, Montevideo and Virginia) were acquired by Finnish patients during travel to Malaysia and Thailand. Isolates were screened for plasmid mediated quinolone resistance by plasmid extraction and by PCR of qnrA, qnrB, qnrS, aac6'-lb-Cr, qepA and oqxB. Positive qnr genotypes were compared with previously identified qnr plasmids by Southern blotting. Transfer of resistance was examined by transformation and subsequent MIC testing of transformants. Mutations in the quinolone resistance determining regions (QRDRs) of gyrA, gyrB, parC and parE were identified by PCR and DHPLC. Efflux activity was assessed by determining accumulation of the fluorescent substrate Hoescht 33342 by all isolates and compared with matched wild strains of the same serovar.

Results: Plasmid mediated quinolone resistance genes were detected in all six isolates. One isolate carried qnrA, two qnrS and three both qnrB and qnrS. aac6'-lb-Cr, qepA and oqxB were not detected. Southern blotting identified qnrS1 in Stanley, Montevideo, Virginia and both Corvallis serovars. All plasmids, when transferred into a wild-type host had increased MICs of ciprofloxacin. In addition, plasmids from Stanley, Mbandaka and Montevideo serovars conferred increased MICs of chloramphenicol and tetracycline. No mutations were detected in the QRDRs of gyrA, gyrB, parC and parE, however, two isolates possessed mutations in gyrA at codon 396 (Leu to Met). All isolates accumulated less Hoescht 33342 than wild-type suggesting increased efflux activity.

Conclusion: These data demonstrate the rise of a highly mobile genotype that confers a novel quinolone resistance phenotype, which has become widely disseminated.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Location: Barcelona, Spain
Presentation type:
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