Poster Presentation International Pasteurellaceae Conference 2014

Identification of dfrA14 in two distinct plasmids conferring trimethoprim resistance in Actinobacillus pleuropneumoniae (#60)

Janine T. Bosse 1 , Yanwen Li 1 , Stephanie Walker 1 , Tom Atherton 1 , Susanna M. Williamson 2 , Jon Rogers 2 , Roy R. Chaudhuri 3 4 , Lucy A. Weinert 3 , Matt T. Holden 5 , Duncan J. Maskell 3 , Alexander W. Tucker 3 , Brendan W. Wren 6 , Andrew N. Rycroft 7 , Paul R. Langford 1 , on behalf of the BRaDP1T Consortium 1 3 6 7
  1. Department of Medicine, Imperial College London, London, UK
  2. Animal Health and Veterinary Laboratories Agency (AHVLA), Bury St Edmunds, UK
  3. Department of Veterinary Medicine, University of Cambridge, Cambridge, UK
  4. Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield, UK
  5. The Pathogen Sequencing Unit, The Wellcome Trust Sanger Institute, Cambridge, UK
  6. Department of Pathogen Molecular Biology, London School of Hygiene & Tropical Medicine, London, UK
  7. Department of Pathology and Pathogen Biology, The Royal Veterinary College, Hatfield, UK

As part of a screen to determine antimicrobial resistance profiles of Actinobacillus pleuropneumoniae (APP) strains in the UK, as well as the genetic basis of resistance, we have identified for the first time the presence of dfrA14 encoding trimethoprim resistance (TMPR) in APP. Of 107 UK clinical isolates collected between 1995 and 2011, 17% were found to be TMPR (MIC >32 mg/L). Analysis of shotgun genome sequence data of the TMPR strains identified the presence of dfrA14 insertionally inactivating strA in all cases. This gene arrangement has previously been reported in Enterobacteriaceae1 2, but never in Pasteurellaceae species. Plasmids were conjugated from selected TMPR APP isolates into an NAD-independent recipient APP strain, with counterselection on BHI containing 25 µg/ml TMP. Isolated plasmids were fully sequenced and confirmed the presence of two different plasmids circulating in UK APP strains. One, a 6050 bp plasmid, contains a sulfonamide resistance gene (sulII) upstream of the ΔstrA::dfrA14 sequence, and an intact streptomycin resistance gene (strB) downstream, as well as the mobilization genes (mobCA) required for conjugation. The other plasmid (6100 bp), does not contain the strB gene, and encodes the sulfonamide resistance gene (sulII) downstream of the ΔstrA::dfrA14 sequence. This plasmid also encodes the mobilization genes (mobCAB). The 6050 bp TMPR plasmid has been in the UK APP population since at least 1998 and the 6100 bp plasmid since at least 2005. Identification of dfrA14 as the gene conferring TMPR in APP strains will facilitate PCR screens for resistance to this important antimicrobial.

Acknowledgements

This work was supported by a Longer and Larger (LoLa) grant from the Biotechnology and Biological Sciences Research Council (grant numbers BB/G020744/1, BB/G019177/1, BB/G019274/1 and BB/G003203/1), the UK Department for Environment, Food and Rural Affairs and Zoetis awarded to the Bacterial Respiratory Diseases of Pigs-1 Technology (BRaDP1T) consortium.

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