Enterococci from Tolminc cheese: Population structure, antibiotic susceptibility and incidence of virulence determinants

Microbiological analysis of ripened artisanal Tolminc cheese revealed the presence of an enterococcal population in numbers of up to 106 per g. All colonies, isolated from the citrate azide tween carbonate (CATC) enterococcal selective medium were Gram positive and coccal-shaped and were analysed with PhenePlate™ FS system. This system discriminated 10 PhP clusters among the 90 enterococcal isolates. From each cluster the most representative isolate for that particular type was selected for further study. The 10 representative enterococci were catalase negative and grew in the presence of NaCl (2%, 4% and 6.5%) and bile salts (0.06%). Genus specific primers confirmed all 10 enterococcal representatives as Enterococcus members, while species specific primers determined them further as strains of Enterococcus faecalis species. PCR for vanA and vanB genes detection, respectively, amplified no PCR products. The absence of van genes was confirmed with both disc and E-test, as isolates were susceptible to vancomycin according to the National Committee for Clinical Laboratory Standards (NCCLS). The results of disc tests with other antimicrobial agents (ampicillin, vancomycin, kanamycin, penicillin, erythromycin, neomycin, chloramphenicol, clindamycin, rifampin) did not differ much among the tested enterococci: they were all very resistant to clindamycin only. The incidence of enterococcus virulence determinants was as expected: all of the 10 E. faecalis strains tested possessed multiple determinants (between 7 and 11).