Characterization of anti-Listeria monocytogenes bacteriocins from Enterococcus faecalis, Enterococcus faecium, and Lactococcus lactis strains isolated from Raïb, a Moroccan traditional fermented milk

Seventy-four samples of raïb, a Moroccan traditional fermented milk, were screened for their anti-Listeria monocytogenes activity. Nine lactic acid bacteria with antilisterial activity were isolated and identified as Lactococcus lactis [4], Enterococcus faecium [4], and E. faecalis [1]. Antibacterial spectra, determined against 45 target strains, led to the selection of four antibacterial-producing strains, which were further characterized. Their anti-microbial agents, inactivated by one or more proteases, were designed as bacteriocins. Lactococcin R9/2 and R10/1 showed the broadest range of inhibitory action. Anti-bacterial spectra and physico-chemical properties suggest that these bacteriocins were similar to nisin. Enterocin R69 had a specificity of action against Listeria spp., whereas Enterocin R18 had a broad spectrum of activity. Lc. lactis R9/2 and E. faecalis R18 were able to coagulate sterilised UHT milk at 30 degrees C in 24 h and induced a 2 log reduction in L. monocytogenes ATCC 15313 population.