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Human feces contain: 1) Chemotrophic anaerobic bacteria (strains XII, 57, IV) identified with D. desulfuricans ssp. faecalis (nov. ssp.) at a level approaching 10 7/g. 2) Organotrophic anaerobic gram positive rods (strains 30, 35, and 43) at between 10(5) and 10 7/g. 3) Chemo-organotrophic anaerobic gram positive rods (strains 22, 27, 47, and 66) were present at 40 5/g. Strains of these two last groups have not been described in the literature and are not found in any accepted toxonomic scheme.

The phenotypes of 153 strains belonging or related to the genus Bijidobacterium were studied. These organisms included 38 collection strains and 115 wild strains (41 strains of human origin, 56 strains of animal origin, and 18 strains obtained from rivers or sewage). Our phenotypic analysis revealed seven main groups that were subdivided into 20 subgroups. Seven subgroups contained no type or collection strain. Among the human strains, the type strains of BiJidobacterium pseudocatenulatum and B . catenulatum fell into group I, which contained the type strains of B. adolescentis (subgroup Ib), B . dentium (subgroup Ic), and B. angulatum (ungrouped). The type strain of B. breve belonged to subgroup IIIal, and the type strains of B . infantis and B . longum fell into subgroup IIIbl. Group VII comprised only wild strains that were isolated from human infant feces. Among the animal strains, group I1 consisted mainly of bifidobacteria that were isolated from pig feces and contained the type strains of B . suis (subgroup IIb), B . thermophilum (subgroup IIf), B . choerinum, and B. boum (ungrouped). Wild strains belonging to group V were isolated from pig, calf, cow, and chicken feces; this included the type strains of B . animalis (subgroup Va), B . magnum (subgroup Vb), B . pseudolongum, and B . globosum (subgroup Vc). The strains of human origin (groups I, 111, and VII) were well separated from the animal strains (groups 11, IV, and V). It was not surprising that the wild strains isolated from surface water or sewage were distributed in the animal groups as well as the human groups. Thus, bifidobacteria can be considered to be successful indicators of human or animal fecal pollution when they are correctly classified. The acidification patterns were not adequate to differentiate Bijidobacterium species, as determined previously by Mitsuoka

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The ingestion of viable bacteria is thought to be required to modify intestinal microflora. In the present study, the effects on fecal flora of consumption of cell-free concentrated whey from milk that had been fermented with Bifidobacterium breve C50 was tested using 10 healthy human volunteers. Results were compared with effects of a commercial milk formula that had been fermented with Streptococcus thermophilus and B. breve C50 and given to 10 control subjects. Nitroreductase and beta-glucuronidase activities were assessed as risk indexes for colon carcinogenesis, and beta-galactosidase was measured as an indicator of the fermentation capacity of the colonic flora. Fecal excretion of Bacteroides fragilis, Clostridium perfringens, and clostridial spores decreased after 7 d of consumption of either preparation; however, counts of bifidobacteria only increased after intake of B. breve whey. Fecal pH was reduced from 7.1 +/- 0.2 to 6.6 +/- 0.3 after intake of whey that had been fermented with Bif. breve. Fecal nitroreductase and beta-glucuronidase significantly decreased, and beta-galactosidase activity increased, after consumption of either preparation. The results indicate that ingestion of viable bifidobacteria was not required to modify intestinal flora of humans. Repression of B. fragilis and clostridia seems to be independent of colonic bifidobacterial overgrowth in humans.