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.
Manson
Janet M
JM
Department of Microbiology, Otago School of Medical Sciences, University of Otago, P.O. Box 56, Dunedin, New Zealand.
Smith
John M B
JM
Cook
Gregory M
GM
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