The human large bowel contains a large variety of bacterial genera, species and strains. Nondigestible food ingredients that escape digestion in the small intestine are thought to be important substrates for some colonic bacteria. The human intestinal bacterial ecosystem has been adapted to nondigestible but fermentable carbohydrates. Ingestion of several nondigestible but fermentable dietary carbohydrates results in a different spectrum of fermented products including the production of a high concentration of short chain organic acids. The most predominant anaerobic bacteria in the colon are able to ferment nondigestible carbohydrates. Moreover, the spectrum of fermented products differs, depending on the amount of carbohydrates. The significance of carbohydrate availability with respect to aromatic amino acid metabolism was shown in fecal batch culture fermentation. Fecal batch culture with arabinogalactan showed a decrease of indole with the cultivation time in two of three cases. Some intestinal bacteria seemed to dissimilate indole. It is the reason why no significant correlation was found between indole and fecal moisture in our previous study.It might be possible to estimate the bowel condition by examining fecal bacterial compositions and other fecal factors such as moisture, concentrations of organic acids and putrefactive products in special cases.

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Characteristic bacterial species inhabit on or in the human body including the skin, mouth, pharynx, stomach, intestine, vagina, urethra, and make up indigenous microbiota.Many of the indigenous bacteria are potential pathogens. If the equilibra are disturbed by certain factors, the potential pathogens may become involved in so-called "opportunistic infections". Disturbances of equilibria are seen in such factors as administration of antibacterial agents or steroid hormones, surgical operations, stresses, diabetes, overwork, aging, etc. During the last 5 decades research on intestinal microbiota has made rapid progress. These are : (1) Development of the method for comprehensive analysis of intestinal microbiota; (2) Classification and differentiation of intestinal anaerobes; (3) Research in intestinal microbial ecology; (4) Role of intestinal flora in health and disease. Thus, intestinal bacteriology has been established. Recent advances of research on intestinal microbiota have led to the appearance of functional foods (probiotics, prebiotics, and biogenics). Although molecular biological methods were introduced for microbiota analysis since the 1980s, they are still under investigation. In the near future, the followings must be investigated. (1) The establishment of molecular methods for qualitative and quantative analysis of intestinal microbiota including scarcity of their numbers. In addition, efforts to characterize taxa of viable but non-culturable bacteria. (2) Research in biochemical properties as well as interactions between microbes, animal host cells, and diets. (3) Functions including immunostimulation, detoxification etc. of intestinal microbiota to enable their use as functional foods for complementary and alternative medicine in both prophylaxis and therapies for life-style related diseases, depressed immune function, inflammatory bowel disease, etc. (4) To advance in these research, unrestricted and evenly liberal cooporation between industry and academic world, as was performrd by me at RIKEN from 1958 to 1992, under taking a leading role in the project by the latter is needed.

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