Bacteriocinogenic activity of lactobacilli isolated from cheese and baby faeces

Lactobacillus strains, isolated from cheese (30 strains) and from baby faeces (41 strains) were examined for bacteriocin production, by deferred agar spot (DAS) test and by agar well diffusion (AWD) assay, using 29 Gram-positive test strains from different genera. Eight cheese isolates and 2 human isolates showed antimicrobial activity against at least one test strain. The proteinaceous nature of the inhibitor was confirmed in four cheese isolates and in both human isolates (LF221 and K7). Human isolates also inhibited some non-LAB bacteria. Strain Lactobacillus acidophilus LF221, was additionally tested by AWD assay against a wide range of bacteria, including pathogens. Besides some lactic acid bacteria test strains, particular strains of the following species were also inhibited: Listeria innocua, Enterococcus faecalis, Bacillus cereus, Staphylococcus aureus and Clostridium sp. The inhibitor was found to be a heat stable protein, as it was inactivated by trypsin, proteinase K, pronase and was resistant to heat (100 degrees C). Strain L. acidophilus LF221 was bactericidal, but not bacteriolytic to Lactobacillus helveticus ATCC 11509. Bacteriocin molecules were present in the supernatant in the form of aggregates with relative molecular masses exceeding 150 kDa.