Persistence of vancomycin-resistant enterococci in New Zealand broilers after discontinuation of avoparcin use

• Published in: Applied and Environmental Microbiology 2004-10, Vol.70 (10), p.5764-5768
• Main Authors: Manson, J.M, Smith, J.M.B, Cook, G.M
• Format: Article
• Language: English
• Subjects: Animal Husbandry; animal pathogenic bacteria; Animals; Anti-Bacterial Agents - administration & dosage; antibiotic resistance; antibiotics; avoparcin; Bacteria; Bacteriology; Biological and medical sciences; broiler chickens; Chickens - microbiology; Disease Reservoirs; DNA fingerprinting; DNA, Bacterial - genetics; DNA, Bacterial - isolation & purification; Drug resistance; Electrophoresis, Gel, Pulsed-Field; Enterococcus durans; Enterococcus faecalis; Enterococcus faecalis - drug effects; Enterococcus faecalis - genetics; Enterococcus faecalis - isolation & purification; Enterococcus faecium; Enterococcus faecium - drug effects; Enterococcus faecium - genetics; Enterococcus faecium - isolation & purification; feed additives; Food Microbiology; Fundamental and applied biological sciences. Psychology; Glycopeptides; Microbiology; New Zealand; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Poultry; poultry production; Public Health Microbiology; pulsed-field gel electrophoresis; vancomycin; Vancomycin Resistance - genetics
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.70.10.5764-5768.2004

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 greater than or equal to 256 microgram/ml for 98.7% of isolates, and the avilamycin MIC was greater than or equal to 8 microgram/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.