Characterization and safety evaluation of enterococci isolated from Spanish goats' milk cheeses

Enterococci are common constituents of dairy products such as cheese, in which it is believed that they contribute to the development of some of their organoleptic properties. This is particularly true in the Mediterranean region, where farmhouse cheeses are generally made from raw milk, which tends to harbour enterococci. In recent years, however, enterococci have emerged as serious pathogens in hospital environments, where vancomycin-resistant strains are on the increase. In this study we have characterized 95 enterococci isolated from 3 different goats' milk cheeses, belonging to the species Enterococcus devriesei, Enterococcus faecalis and E. malodoratus, among others. Genomic typification by RAPD and ERIC-PCR showed that the genotypes tended to be specific to particular cheeses; only two of the different cheeses contained two genotypes. E. malodoratus showed the highest intraspecific diversity. No more than 13% of the isolates demonstrated any antimicrobial activity, most of these belonging to E. devriesei. Screening for the most important enterocin structural genes by dot-blot hybridization proved negative for enterocins A, B and P. All the isolates belonging to E. faecalis, E. hirae and E. avium, on the other hand, hybridized with the enterocin EJ97 gene probe and all the E. faecalis strains hybridized with the AS-48 and MR10A structural gene probes. The genes gelE, esp, asa1, efaA and ace, all associated to virulence factors in enterococci, were detected at different levels in E. faecalis whilst they were not detected in the remaining species studied. No resistance to vancomycin was detected by PCR screening. The gene for tyrosine decarboxylase (tdc) was detected in all the E. faecalis and E. hirae isolates but in none of the others.