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Applied and Environmental Microbiology, January 2006, p. 516-521, Vol. 72, No. 1
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.1.516-521.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Prevalence, Persistence, and Molecular Characterization of Glycopeptide-Resistant Enterococci in Norwegian Poultry and Poultry Farmers 3 to 8 Years after the Ban on Avoparcin

M. Sørum,2* P. J. Johnsen,1 B. Aasnes,1 T. Rosvoll,1 H. Kruse,2 A. Sundsfjord,1,3 and G. S. Simonsen1,3

Department of Microbiology and Virology, Faculty of Medicine, University and University Hospital of North Norway, Tromsø, Norway,1 National Veterinary Institute, Oslo, Norway,2 Norwegian Institute of Public Health, Oslo, Norway3

Received 25 May 2005/ Accepted 20 October 2005

Environmental reservoirs of glycopeptide-resistant enterococci (GRE) in Norway have been linked to former growth promoting use of the glycopeptide avoparcin in poultry production. We have examined the prevalence of fecal GRE in poultry and poultry farmers 3 to 8 years after the Norwegian avoparcin ban in 1995 and performed molecular analyses of the GRE population. Fecal samples from poultry farmers and their flocks on 29 previously avoparcin-exposed farms were collected on five occasions during the study period (1998 to 2003). All flocks (100%) were GRE positive in 1998. Throughout the study period, 78.5% of the poultry samples were GRE positive. Glycopeptide-resistant Enterococcus faecium (GREF) was isolated from 27.6% of the farmer samples in 1998 and from 27.8% of the samples collected between 1998 and 2003. The prevalence of fecal GRE in poultry declined significantly during the study period, but prevalence in samples from the farmers did not decline. PCR analysis revealed a specific Tn1546-plasmid junction fragment in 93.9% of E. faecium isolates. A putative postsegregation killing (PSK) system linked to Tn1546 was detected in 97.1% of the isolates examined. Multilocus sequence typing of glycopeptide-susceptible (n = 10) and -resistant (n = 10) E. faecium isolates from humans (n = 10) and poultry (n = 10) on two farms displayed 17 different sequence types. The study confirms the continuing persistence of a widespread common plasmid-mediated vanA-pRE25-PSK element within a heterogeneous GRE population on Norwegian poultry farms 8 years after the avoparcin ban. Moreover, it suggests an important role of PSK systems in the maintenance of antimicrobial resistance determinants in reservoirs without apparent antimicrobial selection.

* Corresponding author. Mailing address: Section of Bacteriology, National Veterinary Institute, P.O. Box 8156 Dep, 0033 Oslo, Norway. Phone: 0047 23216313. Fax: 0047 23216301. E-mail: marit.sorum{at}vetinst.no

Applied and Environmental Microbiology, January 2006, p. 516-521, Vol. 72, No. 1
0099-2240/06/$08.00+0     doi:10.1128/AEM.72.1.516-521.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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