Antimicrobial resistance, virulence and transmission of enterococci isolated from humans and animals

Abstract

Enterococci are commensal bacteria of humans as well as of animals and major causes of nosocomial infections. Enterococci of animals have potential risks of dissemination to human or transferring their antimicrobial resistance or virulence genes. It is concerned that companion animals can be a reservoir of infectious enterococci. Food, especially provided by food animals, has been also suspected as a carrier of enterococci of animal with antimicrobial resistance and virulence factor. Accordingly, enterococcal isolates from humans and animals were characterized and their epidemiological relation was analyzed in this study. It was carried out to compare the phenotypes and genotypes of antimicrobial resistance and virulence genes from 184 enterococci strains isolated from chickens, pigs, companion animals (dogs and a cat), and human patients in Korea. Then, ampicillin resistant E. faecium (AREF) strains were selected and multilocus sequence typing was performed to investigate the dispersion of clonal complex 17 (CC17), a global epidemic strain, among animals and humans. The companion animal and human isolates showed high resistance rates against ampicillin and ciprofloxacin, whereas food animal isolates from chickens and pigs showed high tetracycline and erythromycin resistance rates. AREF was only detected in human (21 of 21 E. faecium, 100%) and companion animal (3 of 5 E. faecium, 60%) isolates, and all human AREF strains and one of the canine AREF strains were confirmed as CC17. It was suggested that the antibiotic resistance patterns of companion animal isolates were more similar to those of humans than to those of food animals, and CC17 was also detected among only companion animal and human isolates. Companion animal and human E. faecium isolates were characterized and analyzed epidemiologically. Unlike colonization isolates, companion animal infection isolates showed similar CC17 prevalence with human infection isolates. However, patterns of antimicrobial resistance, virulence and pulsed-field gel electrophoresis were different between CC17 isolates from almost all companion animals and humans. From pork meat processing chain, slaughterhouses, processing plants and retails, 339 E. faecalis isolates were isolated and were compared with human infection strains for investigating the dissemination from pork meat to human via pork meat processing chain. From slaughterhouses to retails, chloramphenicol, high-level gentamicin, and erythromycin and multidrug resistance rates decreased while the penicillin resistance rate increased along the processing chain. The prevalence rate of strong or moderate biofilm forming isolates was highest at retails. Random amplified polymorphic DNA-PCR analysis was performed for genetic comparison of the isolates. No isolate seemed to be persistent through the production chain and all the isolates was not similar with human clinical isolates. Therefore, it is suggested that E. faecalis strains from pork meat might not be delivered to humans by consumption of pork meat. In conclusion, the results of the above studies suggested that the transmission of enterococci between animal and human is opportunistic.