Vancomycin-Resistance Phenotypes, Vancomycin-Resistance Genes, and Resistance to Antibiotics of Enterococci Isolated from Food of Animal Origin

In the present study, 500 raw beef, pork, and chicken meat samples and 100 pooled egg samples were analyzed for the presence of vancomycin-resistant enterococci, vancomycin-resistance phenotypes, and resistance genes. Of 141 isolates of enterococci, 88 strains of Enterococcus faecium and 53 strains of E. faecalis were identified. The most prevalent species was E. faecium. Resistance to ampicillin (n=93, 66%), ciprofloxacin (n=74, 52.5%), erythromycin (n=73, 51.8%), penicillin (n=59, 41.8%) and tetracycline (n=52, 36.9%) was observed, while 53.2% (n=75) of the isolates were multiresistant and 15.6% (n=22) were susceptible to all antibiotics. Resistance to vancomycin was exhibited in 34.1% (n=30) of the E. faecium isolates (n=88) and 1.9% (n=1) of the E. faecalis isolates (n=53) using the disc-diffusion test and the E-test. All isolates were tested for vanA and vanB using real-time polymerase chain reaction (PCR) and multiplex PCR, and for vanC, vanD, vanE, vanG genes using multiplex PCR only. Among E. faecalis isolates, no resistance genes were identified. Among the E. faecium isolates, 28 carried the vanA gene when tested by multiplex PCR and 29 when tested with real-time PCR. No isolate carrying the vanC, vanD, vanE, or vanG genes was identified. Melting-curve analysis of the positive real-time PCR E. faecium isolates showed that 22 isolates carried the vanA gene only, 2 isolates the vanB2,3 genes only, and seven isolates carried both the vanA and vanB2,3 genes. Enterococci should be considered a significant zoonotic pathogen and a possible reservoir of genes encoding resistance potentially transferred to other bacterial species.