Avoparcin was used as a feed additive in Norwegian broiler and turkey production from 1986 until 1995. It was banned due to the selection of VanA‐type vancomycin‐resistant enterococci (VRE) in animal husbandry and to reduce the potential for human exposure to VRE. The aim of the present study was to investigate the prevalence of VRE carriage in Norwegian poultry farmers and their poultry three years after avoparcin was banned. Corresponding faecal samples from poultry and humans on farms where avoparcin had previously been used (exposed farms, n = 73) and farms where avoparcin had never been used (unexposed farms, n = 74) were analysed for the presence of VRE. For each farm, one sample from the poultry house and one sample from the farmer were obtained. VRE were isolated from 72 of 73 (99%) and eight of 74 (11%) poultry samples from exposed and unexposed farms, respectively. VRE were isolated from 13 of 73 (18%) and one of 74 (1%) farmer samples from exposed and unexposed farms, respectively. All VRE isolates were highly resistant to vancomycin and possessed the vanA gene, as shown by PCR. The high prevalence of VRE is in accordance with previous Norwegian studies, and shows a remarkable stability of the VanA resistance determinant in an apparently non‐selective environment.
Shiga-toxin-2 (stx 2 )-encoding bacteriophages were isolated from Norwegian Escherichia coli O157 :H7 isolates of cattle and human origin. The phages were characterized by restriction enzyme analysis, hybridization with probes for toxin genes and selected phage DNA such as the P gene, integrase gene and IS1203, and by PCR studies and partial sequencing of selected DNA regions in the integrase to stx 2 region of the phages. The stx 2 -phage-containing bacteria from which inducible phages were detected produced similar amounts of toxin, as shown by a Vero cell assay. The results indicate that the population of stx 2 -carrying phages is heterogeneous, although the phages from epidemiologically linked E. coli O157 :H7 isolates were similar. There appears to have been frequent recombination of stx 2 phages with other lambdoid phages.
Aims: To investigate if cattle on the same farm as sheep are a possible risk factor for stx in sheep and to determine whether or not sheep and cattle on the same farm share the same stx pool. Methods and Results: Faecal samples from sheep and cattle were screened for stx by polymerase chain reaction (PCR). Of these samples, 87AE6 and 64AE6% were stx positive in sheep and cattle, respectively. There was no difference in stx occurrence in sheep from farms with or without cattle. From stx positive samples, 118 Shiga toxin-producing Escherichia coli (STEC) isolates were recovered by a filter-hybridization method. Serotyping, PCR and pulsed-field gel electrophoresis (PFGE) showed that there was a distinct association between serotypes, stx profiles and animal species. Conclusions: Keeping animals together in pens, which enhances faecal-oral contact, is suggested as a possible explanation for the differences seen in stx occurrence. Sheep and cattle isolates are distinctly different in serotype and stx profile although isolated from the same farm, and are more related to isolates within the same serotype with the same stx profile than to isolates with different serotype from the same farm. Significance and Impact of Study: The study supports the animal-host relationship hypothesis suggested in other studies and indicates that the STEC sheep reservoir in Norway may not pose a serious public health risk.
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