Bacteriocin involved in premature death of Lactobacillus acidophilus NCFM during growth at pH 6.

Lactobacillus acidophilus NCFM maintained at pH 6 during growth in lactobacilli MRS broth appeared to exhibit premature death. However, during extended incubation, the culture reinitiated growth. Spent broth collected from the culture when it began the premature death was very toxic to the culture, but growth did occur during extended incubation of the assay tubes. When several successive subcultures with extended incubation were made in MRS broth containing added inhibitory spent broth, a strain (identified as L. acidophilus) was isolated that was resistant to the inhibitor. This strain produced a bacteriocin that was inhibitory to the growth of L. acidophilus NCFM and the predominating strains isolated from it. The producer strain grew more slowly than did the predominating strains in culture NCFM. The results show that when L. acidophilus NCFM, a mixed strain culture, was grown at pH 6, the inhibitory strain was able to grow sufficiently to produce enough bacteriocin to destroy the predominating strain(s) in the culture.