Preliminary characterization of anti-listerial activity in Lactobacillus strains isolated from traditional Italian cheeses

Contamination of some varieties of soft smear cheeses with Listeria monocytogenes is an important problem for the consumer's health, leading to industrial substantial financial losses. Especially smear and soft traditional Italian cheeses such as Taleggio and Gorgonzola, may be risk products from a listeriosis point of view since they constitute a suitable medium for growth of L. monocytogenes. For this reason there is considerable interest in developing microbial ripening consortia which display anti-listerial activity. In this study, 42 Lactobacillus strain isolated from different traditional Italian cheeses surface (Taleggio, Gorgonzola, Casera Valtellina, Scimudin and Formaggio di Fossa) were analyzed for their ability to produce anti-listeria substances. Lactobacillus sakei, L. curvatus, L. plantarum, L. rhamnosus, L. paracasei, L. casei, L. acidophillus and L. acidipiscis, were preliminary screening by an agar spot test and the well diffusion assays. PCR was also performed to search the presence of bacteriocin encoding genes. Although inhibitory activity against L. monocytogenes was detected for all isolates by the agar stop test, the number of positive strains was severely reduced, when the neutralized cell-free supernatants (CFS) were subjected to the well-diffusion assay resulting much less inhibitory against L. monocytogenes. The preliminary characterization of the antimicrobial substances present on the CFS revealed high thermo stability while the sensibility to the treatment with trypsin, proteinase K and papain was different and strain dependent. Based on our results we found 14 news bacteriocin-producing Lactobacillus strains, belong to the genera L. curvatus (8), L. plantarum (2), L. rhamnosus (1), L. casei (1), L. acidophillus (1) and L. acidipiscis (1). According to trycine–SDS–PAGE, these inhibitory actives molecules are approximately 2.5-7 kDa in size. PCR- based analysis demonstrated a great diversity among bacteriocin genes presents in different