L. acidophilus and L. bulgaricus as influenced by surface tension.

Abstract

Following the suggestive report of Albus and Holm 1 on the effect of surface tension on lactobacilli, studies were undertaken with some of the same organisms used by them, and we employed their technic, as described in an unpublished paper generously placed at our disposal. Sodium ricinoleate was used as a depressant, for which we are indebted to Dr. W. P. Larson of the University of Minnesota, who very kindly supplied us with a pure product.

Six strains each of L. bulgaricus and L. acidophilus were tested. While no growth of the former took place in media depressed below 42 dynes, the growth of L. acidophilus was abundant at this point and considerably below. L. acidophilus was inhibited at 35 dynes as measured by the drop-weight method.

The results, therefore, are in close agreement with those of Albus and Holm, and it appears that surface tension may well be considered an effective criterion for differentiating the very closely allied L. acidophilus and L. bulgaricus.