Culture-based approaches have been used for the analysis of human gut microbiota, however, it is difficult to culture 70 to 80% of the bacteria in the human gut. The gut microbiota of adult, elderly, and strictly vegetarian individuals were analyzed by the 16S rRNA gene library and T-RFLP. Among a total of about 1,800 clones obt(ned, approximately 75% of the clones were phylotypes (unexploited bacteria). A large number of species that have not yet been identified exist in the human gut. As a result of phylogenetic analysis, the Clostridium leptum subgroup, the Clostridium coccoides group, and the Bacteroides group were considered to be the predominant bacteria in adult individuals. The C. leptum subgroup, the C. coccoides group, the Bacteroides group, and "Gammaproteobacteria" were detected with high frequency in elderly individuals. In addition, the proportion of the C. coccoides group was lower than that in younger adults. The C. leptum subgroup, the C. coccoides group, the Clostridium rRNA cluster XVIII, and the Bacteroides group were detected in strictly vegetarian individuals. Especially, the Clostridium rRNA cluster XVIII was detected with high frequency. The composition of human gut microbiota was shown by these analyses, and, there were major differences between individuals in the composition of gut microbiota. Microbiota in jejunum, ileum, cecum and recto-sigmoid colon obtained from elderly individuals at autopsy were analyzed using 16S rRNA gene libraries and T-RFLP. The jejunal and ileal microbiota consisted of simple microbial communities that cont(n streptococci, lactobacilli "Gammaproteobacteria", the Enterococcus group, and the Bacteroides group. The cecal and recto-sigmoidal colonic microbiota consisted of complex microbial communities with numerous species (OTUs) that belonged to the C. coccoides group, the C. leptum subgroup, the Bacteroides group and "Gammaproteobacteria". The microbiota group structure was different in each of the four different parts of the human gut. Functional genes were cloned from environmental samples without cultivation of microbes. Novel 1,4-b-xylanase genes, which may contribute to the breakdown of xylan, which cont(ns dietary fiber, were obt(ned directly from mixed genome DNA of fecal microbiota without cultivation. A SOM (Self-Organizing Map) analysis demonstrated that the xylanase gene belongs to the Bacteroidetes.

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Chitosan is a food ingredient recognized as safe, which is produced by deacetylation of aminoacetyl residue in chitin contained in the shells of crabs and shrimps. Chitosan is not digested in the stomach or intestine, but is degraded and digested in the colon by indigenous bacteria such as Bacteroides. A hard capsule made of chitosan was developed to deliver substances to the colon avoiding digestive enzymes in the stomach and intestines. Whether or not the capsule disintegrates in the colon has not yet been tested in humans. In this experiment, a chitosan capsule containing barium sulfate was ingested by healthy male volunteers, and the fate of the capsule was monitored by chronological abdominal radiography. The capsule was shown to disintegrate in the ascending and transverse colon.

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The barrier function of the intestinal mucosa is immature in newborns, and is strengthened by breast milk. We reported previously that systemic bacterial translocation (BT) induced by gastric cannulation in artificially reared (AR) pups continued for 18 days following the gastric cannulation, whereas, systemic BT disappeared within 10 days in sham-operated (Sham) pups reared by a foster parent. In relation to these findings, the purpose of this experiment was to compare phagocytic activity of peritoneal polymorphonuclear leukocytes (PMNL) in AR pups with that in MR pups, and to examine the effects of lipopolysaccharide (LPS) after intra peritoneal (i.p.) injection on the phagocytic activity of PMNL in mother reared (MR) pups. The PMNL were infiltrated with a bovine serum albumin (BSA) i.p. injection 18 h prior to LPS. The cells that phagocytosed FITC-labeled-latex-beads on a cover-glass were counted after May-Grünwald-Giemsa-staining. The phagocytic activity in AR pups was 60% lower at 6 days post-cannulation than that in MR pups. The phagocytic activity in MR pups was time-and dose-dependently decreased after peritoneal injection of LPS. These findings suggest that phagocytic activity of PMNL may be lowered by gram-negative bacteria derived from their systemic BT.

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