The use of avoparcin as a growth promoter and the occurrence of vancomycin-resistant Enterococcus species in Norwegian poultry and swine production

This study documents a strong and statistically significant association bet ween the use of the glycopeptide avoparcin as a growth promoter in Norwegia n poultry production and the occurrence of vancomycin-resistant Enterococcu s species (VRE), Avoparcin was approved as a feed additive for broilers and turkeys in Norway in 1986 and was banned from June 1, 1995. In a survey co nducted in Norway between June, 1995 and March, 1997, VRE were isolated fro m fecal samples from 106 out of 109 poultry houses previously exposed to av oparcin (97%) and from six out of 33 poultry houses never exposed to avopar cin (18%) (RR = 5.35), Samples from previously exposed poultry houses were collected in three time periods. The proportion of positive samples remaine d high (96-98%), in all three time periods indicating a persistence of vanc omycin resistance among enterococci for more than a year and a half after t he withdrawal of avoparcin, VRE were also isolated from six out of 10 poult ry farmers living on farms previously exposed to avoparcin, and from none o f 16 farmers living on farms never exposed to avoparcin, Moreover, VRE were isolated from 68 out of the 225 broiler carcasses investigated (30%), The resistance to vancomycin was a high-level type (MIC greater than or equal t o 256 mu g/ml) mediated by the vanA gene. For comparison, VRE could only be isolated from two out of 147 fecal samples from Norwegian flocks of swine (1%), Because avoparcin never has been used in Norwegian swine production, this observation strengthens the association between the use of avoparcin i n animal husbandry and the occurrence of VRE.