The microbial community in the human colon contains bacteria that reduce cholesterol to coprostanol, but the species responsible for this conversion are still unknown. We describe here the first isolation and characterization of a cholesterol-reducing bacterium of human intestinal origin. Strain D8 was isolated from a 10 ؊8 dilution of a fresh stool sample provided by a senior male volunteer with a high capacity to reduce luminal cholesterol to coprostanol. Cholesterol-to-coprostanol conversion by strain D8 started on the third day, while cells were in stationary phase, and was almost complete after 7 days. Intermediate products (4-cholesten-3-one and coprostanone) were occasionally observed, suggesting an indirect pathway for cholesterol-to-coprostanol conversion. Resting-cell assays showed that strain D8 could reduce 1.5 mol of cholesterol/mg bacterial protein/h. Strain D8 was a gram-negative, non-spore-forming, rod-shaped organism identified as a member of the genus Bacteroides closely related to Bacteroides vulgatus, based on its morphological and biochemical characteristics. The 16S rRNA gene sequence of strain D8 was most similar (>99.5%) to those of two isolates of the recently described species Bacteroides dorei. Phylogenetic tree construction confirmed that Bacteroides sp. strain D8 clustered within an independent clade together with these B. dorei strains. Nevertheless, no cholesterol-reducing activity could be detected in cultures of the B. dorei type strain. Based on Bacteroides group-specific PCR-temporal temperature gradient gel electrophoresis, there was no correlation between the presence of a band comigrating with the band of Bacteroides sp. strain D8 and cholesterol conversion in 11 human fecal samples, indicating that this strain is unlikely to be mainly responsible for cholesterol conversion in the human population.

Purpose: Delayed diarrhea is the most important side effect of irinotecan. The aim of this study was to investigate the role of intestinal microflora on the induction of systemic and intestinal toxicity and diarrhea, studying germ-free and holoxenic mice i.p. injected with irinotecan. Experimental Design: To evaluate the lethal dose, starting with 100 mg/kg/4 d, we treated the holoxenic mice with100, 80, and 60 mg/kg/4 d and germ-free mice with 60, 80,100, and150 mg/ kg/4 d. We recorded the percentage of dead animals, diarrhea, and the epithelial damage to the jejunum, ileum, cecum, and colon at optical and scanning electron microscopy. Results: Germ-free mice were more resistant to irinotecan than the holoxenic group. The lethal dose was between 60 and 80 mg of irinotecan for holoxenic mice and z150 mg for the germ-free. The intestinal damage score was higher in holoxenic than germ-free mice at 100 mg and equally diffuse in the small and large bowel. The damage in germ-free mice was less severe (8 of 40 samples) prevailing in the ileum. The differences were significant for all sites (jejunum, P < 0.001; ileum, P = 0.012; cecum, P = 0.001; colon, P < 0.001). No damage was found in germ-free mice at 60 mg. Diarrhea was present in all 100 and 80 mg holoxenic mice and in 19 of 20 cases at 60 mg whereas it was absent in 60 mg or sporadic in 80 and 100 mg germ-free mice. Conclusions: The intestinal microflora plays a key role in the intestinal toxicity of irinotecan.

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Fourteen microbial strains isolated from conventional rats were inoculated into axenic rats and mice receiving identical diets. The populations of these organisms which became established in the feces of gnotobiotic adult recipient rats and mice were quite similar. The only major difference was that one strain, belonging to the genus Clostridium, disappeared from the feces of gnotobiotic mice, whereas this strain became established in gnotobiotic rats. Most of the strictly anaerobic strains were absent or present only in small numbers before weaning in young rats and mice. A clear-cut barrier effect against Salmonella typhimurium was found in adult gnotobiotic mice colonized with a complex flora derived from a conventional chicken. The microflora established in these recipient mice exerted the same barrier effect when further transferred into axenic chickens. Inoculation of feces from a human donor into adult gnotobiotic recipient mice produced colonization by several strains from the donor, whereas other strains, belonging to the genera Bifidobacterium, Lactobacillus, and Clostridium were present in the donor, but did not persist in recipient mice. In these mice, nonetheless, the colonizing human fecal flora exerted an effective barrier against a toxigenic strain of Clostridium difficile. This barrier effect spontaneously disappeared several weeks later. Administration of clindamycin to the recipient mice led to large variations in the number of viable cells of C. difficile.

The composition of a synthetic medium supporting the growth of lactobacilli is given (Table 1). The medium, containing glucose, amino acids, vitamins, mineral salts, purines and pyrimidines, allows the study of nutritional requirements of different strains of lactobacilli under identical environmental conditions. It was found that all the strains tested needed L‐glutamic acid, L‐valine and L‐leucine, and a group of them also required L‐arginine, L‐tyrosine and L‐tryptophan. Some strains required vitamins, e.g. L. bulgaricus (pantothenic acid), L. fermenti (pantothenic acid and niacin). These results are compared with those found by others employing different media.

The effect of erythromycin base was studied on intestinal resistance to colonization of gnotobiotic mice inoculated with a human fecal flora and challenged with six microbial strains potentially pathogenic for immunocompromised patients. Fecal concentrations of erythromycin were greater than 1,000 micrograms/g in the human donor and in mice. Total intestinal bacterial counts were not significantly different in the human donor and in the recipient mice and were not affected by erythromycin treatment. Strains of various species from the dominant flora (greater than 10(9) colony-forming units/g) and resistant to greater than 1,000 micrograms of erythromycin/ml were present before and persisted during treatment. Strains sensitive to such concentrations - particularly all enterobacteria-were eliminated. Treatment did not reduce colonization resistance against Candida albicans, Clostridium perfringens, and erythromycin-sensitive Escherichia coli. It reduced but did not eliminate some colonization resistance against Pseudomonas aeruginosa, Clostridium difficile, and erythromycin-resistant E coli.

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Gnotohiotic growing rats harbouring either a whole human faecal flora or single human strains of Escherichia coli (EMO) or Bactevoides vulgatus (BVSHl) were fed for 7 weeks on semi-synthetic diets in which the protein source was either soya-bean meal (SM) or rape-seed meal (RM). For each bacterial status the RM-diet group was compared with the control group fed on the S M diet. The association of human faecal flora with the R M diet was responsible for reduced feed intake and reduced weight gain, an enlargement of the liver and thyroid and a decrease in both thyroxine and triiodothyronine plasma levels. The association of the B. vufgatus BVIHl strain with the R M diet reproduced all these effects, except that triiodothyronine plasma levels were not significantly modified. Rats inoculated with the E. coli EM0 strain and fed on the R M diet exhibited a goitre and lowered thyroxine and triiodothyronine plasma levels. These results show that the human intestinal microflora may he involved in glucosinolate metabolism when cruciferous Vegetables are consumed by man. The specificity of the symptoms observed according to the rat bacterial status supports the hypothesis that bacteria yield specific toxic glucosinolate derivatives according to their enzymic potential.