Safety evaluation of enterococci isolated from raw milk and artisanal cheeses made in Slovenia and Serbia

Enterococci represent a significant part of the non-starter LAB microbiota of artisanal cheeses produced mainly from raw milk. Common approaches to safety evaluation of enterococci isolates include assessment of antimicrobial resistance and virulence potential. Hence, a collection of 47 (n = 22, Serbia; n = 25, Slovenia) dairy enterococcal isolates, of which E. faecalis (n = 28), E. faecium (n = 11), E. durans (n = 5), E. casseliflavus (n = 2), and E. gallinarum (n = 1), was analyzed. The susceptibility to 12 antimicrobials was tested using a broth microdilution method, and the presence of the selected antimicrobial resistance and virulence genes was investigated using PCR. Isolates were resistant to tetracycline (TET) (25.5%), erythromycin (ERY) (17.0%), gentamycin and chloramphenicol (CHL) (similar to 6%). No resistance to ampicillin (AMP), ciprofloxacin (CIP), daptomycin (DAP), linezolid (LZD), teicoplanin (TEI), tigecycline (TGC) and vancomycin (VAN) was detected. Among all the resistance determinants analyzed, ermB gene was detected most frequently. All 10 virulence genes analyzed were detected with a distribution of cpd (72.3%), cob and ccf (70.2%), gelE (68.1%), hyl (59.6%), agg (53.2%) and esp (46.8%). The genes encoding cytolysin (cylA, cylM and cylB) were amplified to a lesser extent (21.3%, 21.3% and 12.8%, respectively). However, due to the limited number of enterococci isolates analyzed in the present study, further studies are still required in order to better document the safety status of dairy enterococci.