Skip to main content
Doctoral thesis, 2011

Vancomycin resistant enterococci in Swedish broilers

Nilsson, Oskar


Vancomycin resistance enterococci (VRE) are an important cause of nosocomial infections. Presence of VRE in farm animals constitute a reservoir of resistance that can spread to humans via the food-chain and is due to extensive use of the growth promoter avoparcin conferring cross-resistance to vancomycin. Since 2000, the occurrence of VRE among Swedish broilers has increased in the absence of any obvious selective pressure as avoparcin has not been used since 1984. Also, the increased occurrence seemed to be due to spread of one clone of VRE. The work of this thesis confirms that the increased occurrence of VRE is caused by the spread of one predominant clone. Both the predominant and the minority clones are E. faecium with plasmid mediated vanA gene. The vanA gene is transferrable from the predominant and several of the minority clones. Thus, the predominance of one clone is not due to that the resistance is untransferable from the clones. It also confirms that VRE among Swedish broilers have a potential for zoonotic spread of the vanA gene. Plasmid addiction systems are most likely not involved in the retention of the vanA gene as there is a near absence of such systems among VRE from Swedish broilers. Decreased susceptibility to the ionophore narasin can be co-transferred with the vanA gene from the predominant and some of the minority clones. Thereby the use of narasin for coccidial prophylaxis could contribute to retention of the vanA gene. The traits are probably located close to each other so when retaining the decreased susceptibility to narasin, the enterococci also retain the vanA gene. Broilers arriving to the farms are colonized with VRE persisting in the broiler houses. Differences in occurrence of VRE among farms indicate that the occurrence of VRE can be reduced. Furthermore, a reduction in the contamination of the broiler houses can be achieved by disinfection with a method combining steam and formaldehyde. Subsequently, this could reduce the occurrence of VRE in Swedish broiler production on the whole. Further research should focus on the role of narasin in the VRE epidemiology as well as exploring the possibility to eliminate VRE from Swedish broiler production.


VRE, epidemiology, broiler, vancomycin, vanA, Enterococcus faecium, disinfection, gene transfer, narasin, plasmid addiction system

Published in

Acta Universitatis Agriculturae Sueciae
2011, number: 2011:51
ISBN: 978-91-576-7595-8
Publisher: Department of Clinical Sciences, Swedish University of Agricultural Sciences

Authors' information

Nilsson, Oskar
Swedish University of Agricultural Sciences, Department of Clinical Sciences

UKÄ Subject classification

Clinical Science

URI (permanent link to this page)