Prevalence and Genetic Relatedness of Vancomycin-resistant Enterococci Isolated from Livestock and Humans after Ban of Avoparcin in Korea

Jung, Young Hee; Lee, Yeong Seon; Ahn, Jae Oh; Lee, Ha Rim; Lee, Jeom Kyu; Yoo, Jae Il; Kwak, Hyo Sun; Kim, Bong Su

Abstract

BACKGROUND: Avoparcin, cross-resistance with vancomycin, was added as feed-additive since 1970s and was prohibited in 1997 in Korea. After avoparcin was banned we examined prevalence and genetic relatedness of VRE in enterococci isolated from livestock and humans.
MATERIALS AND METHODS
Using enrichment broth and 6 microgram/mL vancomycin-containing enterococcosel selective agar, vancomycin-resistant enterococci (VRE) were isolated from fecal sample of 255 pigs of 8 farms, 431 chickens of 9 farms, and 328 humans (Food industry employee and Institution cafeteria employee) of 5 public health centers, and 100 raw chicken meats from April to June 2003. Antimicrobial susceptibility was examined by disk diffusion and minimum inhibitory concentrations (MICs), and E-test. Species identification and genotyping were done by multiplex PCR method. Pulsed-field gel electrophoresis (PFGE) of vanA-type VRE isolates was performed by CHEF-Mapper system.
RESULTS
19 isolates from 255 pigs, 122 isolates from 431 chickens, 19 isolates from 100 raw chicken meat, and 7 isolates from 328 humans were resistant to vancomycin. Of the 167 VRE isolates, vanA gene was detected in 141 isolates; 1 isolate (0.4%) in pigs, 121 isolates (28.1%) in chickens, 18 isolates (18.0%) in raw chicken meat, and 1 isolate (0.3%) in humans. Resistant rates of streptomycin, tetracycline, and erythromycin were over 60% in vanA-type E. faecium isolated from poultry. PFGE analysis resulted in two major patterns, F and P types. Also PFGE pattern of 1 VRE from human was identical to that of 1 VRE from poultry.
CONCLUSION
Despite the high prevalence of vanA-type VRE in poultry farms, VRE isolation rate in human was relatively low. This result suggests that the possibility of VRE transmission from poultry to human is low but that possibility may be not ruled out. In PFGE analysis showing 51.5% identical in 2 PFGE patterns, the dissemination of VRE isolates in poultry may be transmitted vertically and horizontally.