Antimicrobial activity and identification of bacteriocin genes in enterococcus and lactococcus strains isolated from italian raw milk and cheeses.

Besides their technological roles, lactic acid bacteria (LAB) also improve the hygiene quality and safety of dairy products by inhibiting competitive natural flora, which include spoilage and pathogenic bacteria As well as producing organic acids, LAB can produce a range of antimicrobial metabolites and bacteriocins, the latter being ribosomally synthesized substances of proteinaceous nature that kill or, at least, inhibit the growth of. some microorganisms. From the screening of 238 lactococcal and enterococcal strains isolated from raw milk and traditional Italian cheeses, we found 19 (10 Enterococcus faecalis, 4 E. faecium and 5 Lactococcus lactis ss lactis) that produced antimicrobial substances. The enterococcal strains were active against Listeria monocytogenes, L. innocua, Staphylococcus aureus and Escherichia coli indicator strains, while the Lc. lactis ss lactis isolates presented a wider spectrum of antimicrobial activity which included Bacillus cereus. Instead, none of the bacteriocin producers inhibited Salmonella enterica. We performed the PCR amplification of known structural genes of nisin and different enterocins (A, AS-48, B, CRL35, L50A and B, P, Q, 1071A and B, mundticin KS and bacteriocin 31). Enterocins A, AS-48, P, Q and bacteriocin 31 genes were detected in the E. faecalis and E. faecium strains, while three Lc. lactis ss lactis harboured the nisin gene. Enterocin AS-48 was the most frequent among the enterocins looked for, and was produced by 10 of the 14 enterococcal isolates. One E. faecium and two E. faecalis isolates harboured different enterocin genes (two, three and five respectively). Bacteriocin identification, and the determination of their spectrum of activity towards a wide range of pathogenic strains, could be useful in defining the applicability of strains as bioprotective starter cultures.