DETECTION OF BACTERIOCINS PRODUCED BY LACTIC-ACID BACTERIA

22 strains of lactic acid bacteria were examined for bacteriocin production and sensitivity using three screening techniques and two media. Distinct inhibition zones were obtained when 9 of 10 strains previously identified in other laboratories as bacteriocin producers were spotted onto yeast extract-supplemented trypticase soy agar without glucose and overlaid with agar seeded with an indicator strain. Of the 12 ATCC strains screened, only Lactobacillus brevis B155 produced bacteriocin. Lactobacillus MRS was not a satisfactory screening medium because the large amunt of acid produced from glucose gave inhibition zones around all strains. The flip-streak deferred-antagonism method was cumbersome and of limited value. The well-diffusion method gave a large number of false-negative results compared to the spot-on-the-lawn method. Lactobacillus sake ATTC 15521 was sensitive to all of the bacteriocins and was chosen as the best indicator strain for further screening studies.