Detection and characterization of bacteriocin-producing Lactococcus lactisstrains

One hundred sixty seven strains of Lactococcus lactis were screened for bac teriocin production by well diffusion assay of GM17 agar. Fourteen (8.4%) p roduced antimicrobial activity other than organic acids, bacteriophages or hydrogen peroxide. The frequency of bacteriocin production ranged from 2% i n L. lactis subsp. cremoris up to 12% in L. lactis subsp. lactis. Antimicro bial activities were not observed in any strain oft. lactis subsp. lactis v ar. diacetylactis. Among thirteen bacteriocin-producing strains and two nis in-producing strains (L. lactis subsp. lactis ATCC 11454 and L. lactis subs p. lactis CNRZ 150), eight (53%) were characterized as lactose-positive (La c(+)) 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 st rains (ITAL 435, ITAL 436, ITAL 437 and ITAL 438) showed identical profiles and the other were quite distinct.