ABSTRACT
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 pH. Only the strain "L. lactis" subsp. "lactis" ITAL 383 produced a bacteriocin with a wide activity spectrum, similar to nisin of "L. lactis" ATCC 11454. This bacteriocin inhibited closely related species and other Gram-positive microorganisms including "Listeria monocytogenes" and "Staphylococcus", 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.
Subject(s)
Bacteriocins , In Vitro Techniques , Lactococcus lactis , Nisin , Spectrum AnalysisABSTRACT
One hundred sixty strains of Lactococcus lactis were screened for bacteriocin production by well diffusion assay of GM17 agar. Fourteen (8.4 per cent) produced antimicrobial activity other than organic acids, bacteriophages or hydrogen peroxide. The frequency of bacteriocin production ranged from 2(per cent) in L.lactis subsp. cremoris up to 12(per cent) 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 per cent) 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.