Antagonistic activity against foodborne-pathogens of lactic acid bacteria from Calabrian raw milk cheeses

Background and aims: Previous studies have been carried out to select Escherichia coli-inhibiting strains of Lactobacillus paracasei subsp. paracasei isolated from raw milk cheeses. This study aims to select foodborne pathogen-inhibiting strains of lactic acid bacteria useful as adjunct cultures in cheese manufacturing. Methods: Lactic acid bacteria have been isolated from eight samples of the artisanal ewes’ milk cheeses Pecorino del Poro and Pecorino d’Aspromonte and from four samples of the artisanal goats’ milk cheese Caprino d’Aspromonte, made without the addition of starters. The lactic acid bacteria have been identified, characterised, and tested by spot method in Petri plate against 5 strains of dairy E. coli and against a reference E. coli strain (ATCC 45922). The strains showing antagonistic activity against the dairy E. coli strains have been tested against the following foodborne-pathogens: verocytotoxin-producing Escherichia coli (VTEC) O157:H7, VTEC E. coli O26, Listeria monocytogenes, Salmonella spp., S. typhimurium, and enterotoxigenic Staphylococcus aureus. Two control strains of L. paracasei subsp. paracasei have been used. Results: The lactic acid bacteria isolated were 17 coccal-shaped and 51 rod-shaped. Only the rod-shaped strain have showed antagonistic activity against the dairy E. coli and the E. coli reference strain. Eight strains of Lactobacillus spp. have been tested in Petri plate against the pathogens, exhibiting different behaviours: three strains showed inhibiting activity against all the pathogens; the other five strains showed activity against some of them. The two L. paracasei subsp. paracasei strains were active against the tested pathogens, with the exclusion of VTEC O157:H7 and O26. The observed antagonistic activity was presumably due to bacteriocin-like compound production. Conclusions: Using expressly selected lactic acid bacteria as adjunct cultures could be an effective strategy to protect artisanal raw milk cheeses against foodborne-pathogens, so improving their safety.