The Production of a Growth Inhibitor by Lactic Streptococci

probably was the first to show that lactic streptococci may inhibit growth of another lactic organism. He found that Streptococcus lactis inhibited acid production by Lactobacillus bulgaricus when the two organisms were grown together in making buttermilk. Whitehead and Ridder (14) and later Meanwell (8) isolated from "non-acid" or "slow" milks lactic streptococci which, when grown in normal milk, rendered it unsuitable for growth of starter organisms. Oxford (9) studied two of the cultures isolated by MeanweU and concluded that they produced a "protein-like substance of small molecular weight" which caused the inhibition of other organisms. He called the substance "diplocoeein." Hunter and Whitehead (5) observed that most strains of Streptococcus eremoris and most of the commercial mixed starter cultures tested by them grew poorly in milk in which inhibitory lactic organisms had previously grown, although certain strains grew normally. About one-fourth of the cultures of S. cremoris isolated from commercial starters by Hoyle and Nichols (4) were inhibitory to a test culture of S. cremoris. These workers also found that about one-third of the cultures of S./actis isolated by them from raw milk were inhibitory, and to a greater degree than were the cultures of S. cremoris.