Abstract
Avoparcin was used as a feed additive in New Zealand broiler production from 1977 until June 2000. We report here on the effects of the usage and discontinuation of avoparcin on the prevalence of vancomycin-resistant enterococci (VRE) in broilers. Eighty-two VRE isolates were recovered from poultry fecal samples between 2000 and mid-2001. VRE isolates were only obtained from broiler farms that were using, or had previously used, avoparcin as a dietary supplement. Of these VRE isolates, 73 (89%) were VanA-type
Enterococcus faecalis
and nine (11%) were VanA-type
Enterococcus faecium
. All
E. faecalis
isolates were found to have an identical or closely related pulsed-field gel electrophoresis (PFGE) pattern of
Sma
I-digested DNA and were susceptible to both ampicillin and gentamicin. The PFGE patterns of the nine
E. faecium
isolates were heterogeneous. All VRE contained both the
vanA
and
ermB
genes, which, regardless of species or PFGE pattern, resided on the same plasmid. Eighty-seven percent of the VRE isolates also harbored the
tet
(M) gene, while for 63 and 100%, respectively, of these isolates, the avilamycin and bacitracin MICs were high (≥256 μg/ml). Five of eight vancomycin-resistant
E. faecalis
isolates recovered from humans in New Zealand revealed a PFGE pattern identical or closely related to that of the
E. faecalis
poultry VRE isolates. Molecular characterization of Tn
1546
-like elements from the VRE showed that identical transposons were present in isolates from poultry and humans. Based on the findings presented here, a clonal lineage of VanA-type
E. faecalis
dominates in VRE isolated from poultry and humans in New Zealand.