Persistence of vancomycin-resistant enterococci in New Zealand broilers after discontinuation of avoparcin use.
Large amounts of tylosin, zinc-bacitracin, and avilamycin are currently used as prophylactics in New Zealand broiler production. Avoparcin was also used from 1977 to 2000. A total of 382 enterococci were isolated from 213 fecal samples (147 individual poultry farms) using enrichment broths plated on m-Enterococcus agar lacking antimicrobials. These isolates were then examined to determine the prevalence of antimicrobial resistance. Of the 382 isolates, 5.8% (22 isolates) were resistant to vancomycin, and 64.7% were resistant to erythromycin. The bacitracin MIC was > or =256 microg/ml for 98.7% of isolates, and the avilamycin MIC was > or =8 microg/ml for 14.9% of isolates. No resistance to ampicillin or gentamicin was detected. Of the 22 vancomycin-resistant enterococci (VRE) isolates, 18 (81.8%) were Enterococcus faecalis, 3 were Enterococcus faecium, and 1 was Enterococcus durans. However, when the 213 fecal enrichment broths were plated on m-Enterococcus agar containing vancomycin, 86 VRE were recovered; 66% of these isolates were E. faecium and the remainder were E. faecalis. Vancomycin-resistant E. faecium isolates were found to have heterogenous pulsed-field gel electrophoresis (PFGE) patterns of SmaI-digested DNA, whereas the PFGE patterns of vancomycin-resistant E. faecalis isolates were identical or closely related, suggesting that this VRE clone is widespread throughout New Zealand. These data demonstrate that vancomycin-resistant E. faecalis persists in the absence and presence of vancomycin-selective pressure, thus explaining the dominance of this VRE clone even in the absence of avoparcin.
Department of Microbiology, Otago School of Medical Sciences, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Janet M
JM
Manson
John M B
JM
Smith
Gregory M
GM
Cook
D000822:Animal Husbandry; D000818:Animals; D000900:Anti-Bacterial Agents / Q000008:administration & dosage; D002645:Chickens / Q000382:microbiology*; D004269:DNA, Bacterial / Q000235:genetics / Q000302:isolation & purification; D004197:Disease Reservoirs; D016521:Electrophoresis, Gel, Pulsed-Field; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D016984:Enterococcus faecium / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification*; D005516:Food Microbiology; D006020:Glycopeptides; D009520:New Zealand; D020713:Vancomycin Resistance / Q000235:genetics
D000900:Anti-Bacterial Agents; D004269:DNA, Bacterial; D006020:Glycopeptides; C016249:avoparcin