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Some Characteristics of the Growth Inhibitor Produced by a Lactic Streptococcus^{1, 2,}

Department of Bacteriology, University of Wisconsin, Madison

ABSTRACT

The inhibitory substance produced by one strain of Streptococcus lactis was associated with the cells that produced it but was liberated from them by acid. Boiling or autoelaving a culture of S. lactis for 10 min. at pH 4.8 had little effect on its inhibitory activity but heating at pH 7.4 rapidly destroyed about half of the inhibitor in the culture. It is believed that the inhibitor is somehow protected from destruction by heating at neutral or alkaline reactions when it is attached to the cells, but when released into the culture medium it is rapidly destroyed by this treatment. At acid reactions it is relatively stable to heat whether bound to the cells or not.

The inhibitory material was not only more stable but it was also more active at acid reactions.

Its ability to inhibit a test culture of Lactohacillus casei was markedly increased when the reaction of the culture medium was below pH 5.4.

¹ Published with the permission of the Director of the Wisconsin Agricultural Experiment Station.

² This work was supported in part by funds supplied by the Wisconsin Alumni Besearch Foundation.

³ Current address: The Western Condensing Co., Appleton, Wisconsin.