A total of 285 samples of meat and meat products were evaluated for the presence of bacteriocin-producing lactic acid bacteria by the "sandwich" test. From 174 of these samples, 813 strains of lactic acid bacteria were isolated. They were able to inhibit the growth of Staphylococcus aureus CTC 33 and/or Listeria innocua Lin 11. When evaluated by the well-diffusion assay, 128 of these strains inhibited the growth of the indicator strains. The inhibitory spectra of activity of the isolates were evaluated against a range of Gram-positive and Gramnegative test organisms. S. aureus was the most sensitive indicator tested, whereas Enterococcus faecalis and Lactobacillus plantarum were the most resistant ones. All the compounds produced by the lactic acid bacteria were fully or partially inactivated by some of the proteolytic enzymes, which indicates their proteinaceous nature. The antimicrobial activity of the bacteriocins produced by the lactic acid bacteria isolated in this work could act as a potential barrier to inhibit the growth of spoilage bacteria and foodborne pathogens.

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Bacteriocins produced by fifteen strains of Lactococcus lactis (14 L. lactis subsp. lactis and one L. lactis subsp. cremoris) were heat resistant, sensitive to several proteolytic enzymes and active over a wide range of pH. Their resistance to the heating was greatly influenced by the pH. Only the strain L. lactis subsp. lactis ITAL 383 produced a bacteriocin with a wide activity spectrum, similar to nisin of L. lactis subsp. lactis ATCC 11454. This bacteriocin inhibited closely related species and other Gram-positive microorganisms including Listeria monocytogenes and Staphylococcus aureus, but it was not active against the Gram-negative bacteria tested. The identification of partially purified antimicrobial compounds by SDS-PAGE showed that bacteriocin produced by strain ITAL 383 had the same molecular weight of nisin produced by L. lactis subsp. lactis ATCC 11454.

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One hundred sixty seven strains of Lactococcus lactis were screened for bacteriocin production by well diffusion assay of GM17 agar. Fourteen (8.4%) produced antimicrobial activity other than organic acids, bacteriophages or hydrogen peroxide. The frequency of bacteriocin production ranged from 2% in L. lactis subsp. cremoris up to 12% in L. lactis subsp. lactis. Antimicrobial activities were not observed in any strain of L. lactis subsp. lactis var. diacetylactis. Among thirteen bacteriocin-producing strains and two nisin-producing strains (L. lactis subsp. lactis ATCC 11454 and L. lactis subsp. lactis CNRZ 150), eight (53%) were characterized as lactose-positive (Lac + ) and proteinase-negative (Prt -). The bacteriocin-producing cultures were also characterized on the basis of plasmid content. All strains had 2 to 7 plasmids with molecular weights varying from 0.5 to 28.1 Mdal. Four strains (ITAL 435, ITAL 436, ITAL 437 and ITAL 438) showed identical profiles and the other were quite distinct.