ANALYSIS OF LACTOBACILLUS PHAGES AND BACTERIOCINS IN AMERICAN DAIRY-PRODUCTS AND CHARACTERIZATION OF A PHAGE ISOLATED FROM YOGURT

Yogurt and acidophilus milk that contain Lactobacillus acidophilus cou ld promote human health because L. acidophilus can inhibit enteric and food-borne microbial pathogens. To evaluate the stability of dairy L. acidophilus cultures, we studied whether some dairy lactobacilli coul d be inhibited by phages or bacteriocins released by other dairy lacto bacilli, From 20 yogurts and two acidophilus milks purchased at local food markets, 38 Lactobacillus strains were isolated, Eight Lactobacil lus type strains were used as controls. With mitomycin induction and a gar spot assay, phages and bacteriocins were isolated from these strai ns and their activities were analyzed, Lactobacillus strains from 11 y ogurts released phages, while the strains from most of the remaining p roducts released bacteriocins, One phage, designated phi y8, was chara cterized, It was spontaneously released from its host strain, L. acido philus Y8, at a rate of about 10(4)/ml, This phage lysed nine other da ily Lactobacillus strains tested, It had a burst size of 100, an elong ated prolate head of 39 by 130 nm, a long, flexible but noncontractile tail of 300 nm, and a 54.3-kb linear double-stranded DNA. DNA fingerp rinting analysis indicated that L. acidophilus phages of nine yogurts in this study belonged to the same type as phi y8, Although they may b e sensitive to bacteriocins, all lysogens resisted further phage attac ks, whereas most nonlysogens were sensitive to both phages and bacteri ocins, Therefore, Lactobacillus cultures of some American yogurts and acidophilus milks may be unstable or unsafe because they can either he inhibited by phages or bacteriocins or release them to inhibit lactob acilli of other dairy products.