Nobuo Suegara

Studies on streptococci. II. Colonization of lactic acid bacteria isolated from rats and humans in the gastrointestinal tract of rats.

The population levels of bacteria in the contents and the walls of the gastrointestinal tract of gnotobiotic rats inoculated with lactic acid bacteria (streptococci, lactobacilli, and bifidobacteria) from humans and rats were determined. Lactobacilli as well as streptococci isolated from rats colonized in the digestive tracts of the gnotobiotic rats at a high population level, characteristically highest in the stomach. On the other hand, in the rats inoculated with human lactic acid bacteria, streptococci were dominant in the lower tract. The human lactobacilli or bifidobacteria did not colonize when the organisms in each genus were inoculated together with streptococci. However, when all three genera were inoculated together, lactobacilli and bifidobacteria colonized. Observations on the species of streptococci showed that the intestinal type of streptococci was found to colonize at a high population level, but the oral type was not. Strains of the same genus of lactic acid bacteria from humans and from rats showed different colonization patterns.

Distribution of Indigenous Lactobacilli in the Digestive Tract of Conventional and Gnotobiotic Rats

Distribution of indigenous lactobacilli in the gastrointestinal tracts of rats was investigated at the species level. The indigenous lactobacilli isolated from conventional rats were divided into three groups, Lactobacillus acidophilus and its related strains, L. fermentum, and L. murini. Localization of the Lactobacillus groups in the gastrointestinal tracts could be distinguished clearly based on arabinose and glucose fermentation reaction of isolates from each part of the gastrointestinal tract. Group I (L. acidophilus and the related strains) and Group II (L. fermentum) were the major populations of lactobacilli on the walls of the non‐glandular part and in the contents of the stomachs of both conventional and gnotobiotic rats. Group I predominated in all the parts of the digestive tract of conventional rats, whereas Group II was in the minority in the lower part of the gastrointestinal tracts of both groups of rats. Group III (L. murini) was the predominant population of Lactobacillus in the lower part of small intestine of conventional rats and in all parts of the gastrointestinal tracts of gnotobiotic rats except for the wall of the non‐glandular part of the stomach.

Intestinal microflora and aging: Age-related change of lipid metabolism in germ-free and conventional rats

The influence of intestinal microflora and aging on the lipid metabolism in germ-free (GF) and conventional (CV) rats, 8 and 40 weeks old, was investigated. Serum cholesterol at the age of 8 and 40 weeks and serum triglyceride (TG) at the age of 40 weeks was higher in GF than in CV rats. Serum cholesterol decreased and serum TG and corticosterone tended to increase in both GF and CV rats with aging. In the rats 40 weeks of age, lipase activity of the pancreas and the duodenal, jejunal, and colorectal contents in GF rats increased, but that of the ileal and cecal contents in GF and CV rats decreased. Intestinal microflora tended to depress the age-related increase of serum TG and lipase activity of the pancreas and the duodenal and jejunal contents. Lipoprotein lipase (LPL) and hormone-sensitive lipase (HSL) activities of the epididymal adipose tissue were higher in CV than in GF rats at both 8 to 40 weeks of age. The LPL activity increased and the HSL activity decreased in both GF and CV rats with aging. The concentration of cholesterol increased and that of bile acids decreased in the cecal contents of 40-week-old GF rats.