Plasmid-mediated quinolone resistance determinant qnrS1 found in Salmonella enterica strains isolated in the UK

Katie L. Hopkins*, Lara Wootton, Martin Day, E. John Threlfall

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    87 Citations (Scopus)


    Objectives: To determine the prevalence of qnr genes in selected Salmonella enterica and Escherichia coli isolated in the UK. Methods: One hundred and eighteen S. enterica and 103 E. coli were screened for qnrA, qnrB and qnrS by PCR. Transferability of qnr plasmids was assessed and isolated plasmids compared with previously identified qnr plasmids by restriction fragment length polymorphism analysis and hybridization experiments. PCRs and sequencing identified co-transferred β-lactamase genes and mutations in the quinolone resistance-determining region of gyrA. Results: Only six S. enterica strains belonging to four serotypes (Stanley, Typhimurium, Virchow and Virginia) were positive for qnrS1. qnrS1 was present on plasmids of 13.5 kb (TPqnrS-1a and -1b) in Typhimurium and Virginia isolates, 44 kb (TPqnrS-2) in two Virchow isolates and >148 kb (TPqnrS-3a and -3b) in two Stanley isolates. blaTEM-1 and a group 9 blaCTX-M were co-transferred on TPqnrS-2 and TPqnrS-3b. Hybridization of a qnrS1 probe to digested qnrS1 plasmids suggested qnrS1 on TPqnrS-2 may be located in a similar genetic environment to Shigella qnrS plasmid pAH0376, but in a different environment in the other plasmids. Conclusions: This is the first report of plasmid-mediated quinolone resistance in a Salmonella isolate from the UK; five isolates were associated with foreign travel to, or food imported from, the Far East. The presence of qnrS1 on different plasmid backbones in several Salmonella serotypes suggests successful dissemination of plasmids or qnrS1. It is of concern that qnrS1 is being identified in Salmonella serotypes that are commonly implicated in human infection in the UK. Coupled with β-lactam resistance, it may compromise treatment of vulnerable patient groups.

    Original languageEnglish
    Pages (from-to)1071-1075
    Number of pages5
    JournalJournal of Antimicrobial Chemotherapy
    Issue number6
    Publication statusPublished - Jun 2007

    Bibliographical note

    Funding Information:
    We would like to thank George Jacoby, Lahey Clinic, USA, for providing pMG252 and pMG298 and Mami Hata, Aichi Prefectural Institute of Public Health, Japan, and Myonsun Yoh, Research Institute for Microbial Diseases, Osaka University, Japan, for providing pAH0376. Part of this study was presented at the Forty-sixth Interscience Conference on Antimicrobial Agents and Chemotherapy (San Francisco, CA, USA, 2006; Poster C2-0088). This study was funded by the Department of Environment, Food and Rural Affairs, UK, project VM02136.


    • Fluoroquinolones
    • Molecular epidemiology
    • Plasmids


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