THE EFFECT OF DIET ON THE FECAL BACTERIAL FLORA OF MICE AND ON THEIR RESISTANCE TO INFECTION

Abstract
A study was made of the effect of certain dietary regimens on the lactobacillus flora in the stools of mice and on their resistance to infection. Semi-synthetic diets with purified casein or wheat gluten as sole source of protein, gave rise to much smaller numbers of viable lactobacilli in the stools than did other diets containing unidentified natural products - as present for example in mixtures of whole wheat and whole milk, or in certain commercial pellets. Furthermore, one of the lactobacillus types with rhizoid morphology disappeared completely from the stools of animals fed the semi-synthetic diet. The change in the lactobacillus flora became apparent within a very few days after the animals had been shifted from the complex to the synthetic diet. Moreover, this change was not completely reversible. Whereas the total numbers of lactobacilli increased when the animals were shifted back from the synthetic to the complex diets, the rhizoid lactobacilli which had disappeared completely from the stools reappeared only slowly or not at all. In 12 consecutive experiments the 3 diets which gave rise to the large numbers of lactobacilli in the stools also conferred on the mice a much higher resistance to experimental infection with Staphylococcus aureus and Klebsiella pneumoniae, than did the semi-synthetic diets.

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