Diet and the equilibrium between bacteria and yeast implanted in gnotobiotic rats

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Abstract
Ten strains of strictly anaerobic bacteria belonging to the genera Acuformis, Inflabilis, Clostridium, Streptococcus (two strains, S1 and S2), Veillonella, Eubactrium, Zymobacterium, Ristella, and Pasteurella; three strains of facultatively anaerobic bacteria belonging to the genera Lactobacillus, Staphylococcus, and Actinobacillus; and one yeast strain of the genus Torulopsis, were inoculated successively into germfree rats fed a semisynthetic diet. The Acuformis strain established in the digestive tract of rats only if the Ristella strain was already established there. When the 14 strains were established, the equilibrium between the strains was as follows: Pasteurella constituted the dominant population, and the number of viable cells varied little as a function of time; Ristella, Eubacterium, Streptococcus (strains S1 and S2), Acuformis, Veillonella, Lactobacillus, and Clostridium were 10- to 100-fold less abundant than Pasteurella, and the numbers of viable cells of Acuformis, Ristella, and Streptococcus (strain S2) decreased progressively as a function of time while those of other strains varied little. Inflabilis, Zymobacterium, Torulopsis, Actinobacillus, and Staphylococcus, which constituted the subdominant population, were 100- to 10,000-fold less abundant than Pasteurella, and the numbers of viable cells of Inflabilis, Zymobacterium, Torulopsis, and Staphylococcus varied a great deal as a function of time. When lactose was added to the diet of tetradecaphoric rats, the total number of viable cells increased tenfold and reached 5 x 1010/g of feces, but the basic equilibrium between the 14 strains was almost unchanged. It was observed that the number of viable cells of Acuformis and Lactobacillus increased 100-fold and that of Pasteurella and Veillonella increased 10- to 50-fold; whereas that of Streptococcus (strain S2) decreased tenfold. There were great differences in the localization of the 14 strains along the digestive tract of the tetradecaphoric rats. Facultatively anaerobic strains and two strictly anaerobic strains, Acuformis and Clostridium, were dominant in the stomach and small intestine where the other strains were present only in small numbers, whereas the strictly anaerobic strains were dominant in the cecum and colon, where strains of Staphylococcus, Actinobacillus, and Torulopsis were subdominant. There was a reduction in cecal size in the tetradecaphoric animals to the level seen in homologous classic rats. Preliminary results of histological study showed also that the cecal mucosa presented a number of features characteristic of classic rats. The bacterial strains used in this study did not, however, form dense layers on the cecal mucosa. On the other hand, with immunofluorescent techniques, Lactobacillus, Acuformis, and Staphylococcus were seen to be attached to the upper layers of squamous epithelium in the nonglandular portion of the stomach.

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