JAC Advance Access originally published online on June 8, 2007
Journal of Antimicrobial Chemotherapy 2007 60(2):263-268; doi:10.1093/jac/dkm186
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Transposon characterization of vancomycin-resistant Enterococcus faecium (VREF) and dissemination of resistance associated with transferable plasmids
1 Antimicrobial Resistance Unit, National Food Institute, Danish Technical University, Bülowsvej 27, DK-1790 Copenhagen V, Denmark 2 Department of Food and Environmental Safety, Veterinary Laboratories Agency—Weybridge, Addlestone, Surrey KT15 3NB, UK
Received 6 March 2007; returned 19 March 2007; revised 17 April 2007; accepted 1 May 2007
* Corresponding author. Tel: +45-72-34-61-04; Fax: +45-72-34-60-01; E-mail: l.garcia-migura{at}liverpool.ac.uk
Objectives: VanA glycopeptide resistance has persisted on broiler farms in the UK despite the absence of the antimicrobial selective pressure, avoparcin. This study aimed to investigate the contribution of horizontal gene transfer of Tn1546 versus clonal spread in the dissemination of the resistance.
Methods and results: One hundred and one vancomycin-resistant Enterococcus faecium isolated from 19 unrelated farms have been investigated. Tn1546 characterization by long PCR and ClaI-digestions of amplicons showed a very low diversity of Tn types (n = 4) in comparison to the high genotypic diversity demonstrated by PFGE (n = 62). Conjugation experiments were carried out to assess the transfer of vancomycin resistance. Co-transfer of vanA together with erm(B) positioned on the same conjugative plasmid containing a replicon similar to pRE25 was demonstrated and also the presence of different plasmid replicons, associated with antimicrobial resistance on several unrelated farms.
Conclusions: Horizontal transfer of vancomycin resistance may play a more important role in the persistence of antimicrobial resistance than clonal spread. The presence of different plasmid replicons, associated with antimicrobial resistance on several unrelated farms, illustrates the ability of these enterococci to acquire and disseminate mobile genetic elements within integrated livestock systems.
Keywords: broiler , Tn1546 , horizontal transfer , replicon typing
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