Evidence for a bacteriocin-like substance produced by a new strain of Streptococcus sp., inhibitory to gram-positive food-borne pathogens.

A new strain of Streptococcus sp. (CNCM I-841) isolated from a commercial probiotic product was shown to be antagonistic towards several food-borne pathogens including Clostridium sp. and Listeria monocytogenes. This strain produced and excreted an antibacterial substance in MRS broth. The inhibitory substance was different from hydrogen peroxide, since it was unaffected by catalase. It was sensitive to proteolytic enzymes, indicating that the active moiety of the inhibitor was proteinaceous in nature, and it had no effect on its producer strain. These properties suggested that the inhibitory substance could be considered as a bacteriocin-like substance. The antimicrobial substance was also produced in M17 and tryptose broths if they were supplemented with Tween-80. Partial purification allowed a 10.5-fold increase in the specific activity. A preliminary characterization showed that it was active against lactobacilli, Enterococcus faecalis, Clostridium sp. and Listeria sp. It was not affected by 2-h treatment at 60 degrees C, but was sensitive to treatments at 100 degrees C and to autoclaving at 121 degrees C. The activity was not affected by treatments at pH values ranging from 2 to 11.