The bactericidal action of fermented milk on
Escherichia coli var. communis was investigated experimentally.
1) The sterilizing power of fermented milk, displayed when
E. coli is inoculated directly in it, acts on
E. coli very vigorously, and at pH 3.6, it takes about 30 minutes for the milk to sterilize the germs in it.
2) When the latex in which both lactic-acid baceria and
E. coli are contained, is made to fermented milk, the
E. coli in fermented milk lives for a much loger period than that mentioned above.(SeeFigs. 3 & 4).
3) The amount of viable
E. coli fermented with lactic-acid bacteria in milk increases until the pH reaches 4. After that, it rapidly decreases to zero at pH3.5-3.6 if the fermentation continues (See Figs. 2 & 4).
4) If the fermented milk is refrigerated during the process of fermentation for the purpose of suppressing or stopping the metabolism of
E. coli, the
E. coli lives for a very long time even in the pH range in which the bactericidal action might be displayed (See Fig. 5).
5) The principal cause of the bactericidal action of fermented milk is lactic acid produced by lactic culture.
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