Production of bacteriocins active against Listeria monocytogenes and Listeria innocua from dairy enterococci

One hundred and sixteen strains of enterococci were screened for antagonistic activities against other micro-organisms, including pathogenic or spoilage bacteria such as Listeria monocytogenes and Clostridium tyrobutyricum. Several strains belonging to Enterococcus faecalis and Enterococcus faecium produced bacteriocins with a wide activity spectrum. Five bacteriocins were further characterized. Bacteriocins were produced as secondary metabolities in both liquid synthetic media and milk, were insensitive to rennet and heat stable. In milk, bacteriocins were produced during incubation either at 37°C or under a temperature gradient reproducing the first 24 h of soft cheese manufacture. The antimicrobial activity form E. faecium strain 7C5 remained stable in milk until the end of the incubation period. The cell-free culture supernatants from producer strains exhibited a bactericidal mode of action on L. innocua. In mixed cultures with E. faecium 7C5, growth of L. innocua was strongly inhibited by bacteriocin production. The Enterococcus spp. bacteriocins studied showed some useful characteristics for technological applications.