Enterococcus faecalis and Enterococcus faecium in pasteurized milk: Prevalence, genotyping, and characterization of virulence traits

To assess the prevalence of enterococci in pasteurized milk and characterize their virulence traits, 416 pasteurized milk samples were purchased from retail stores in the Northwest of Iran. Enterococci were isolated by conventional methods and confirmed by genus-specific PCR. Amongst the samples, 269 were identified as either Enterococcus faecalis or E. faecium, which were then subjected to genotypic and phenotypic analyses. Using enterobacterial repetitive intergenic consensus (ERIC)-PCR, E. faecalis and E. faecium strains were effectively grouped into 15 and 16 clusters, respectively. Nonetheless, ERIC-PCR was unable to accurately cluster E. faecalis and E. faecium strains according to their virulence or phenotypic characteristics. Based on the results, most of the isolates, especially E. faecalis strains, carried gelE, hyl, asa1, esp, cylA, ace, and efaA genes. Results also revealed that E. faecalis and E. faecium isolates were highly resistant to most of the tested antibiotics. The resistance to vancomycin for E. faecalis and E. faecium was estimated at 71.9% and 77.6%, respectively. Moreover, 81% and 69% of E. faecalis and E. faecium strains were able to produce biofilm. It was concluded that pasteurized milk could be an intermediate vehicle for the transmission of multidrug-resistant virulent enterococci strains to humans.