The intestinal microbiota is composed of hundreds of species in tens of genera of facultative and anaerobic members of the domains Bacteria and Archaea. Its population exceeds 1×10¹⁴ microbial cells. Its mass is one-half that of intestinal content. It influences many physiological and immunological properties of its animal host. This knowledge supports two concepts: 1. the microbiota is an organ of the body essential for survival of man in the natural world, and 2. humans are composites of eukaryotic animal cells and bacterial and archeal members of the biota. These concepts have important implications for research during the 21st Century on human biology and evolution, advancing health, and diagnosis and treatment of disease. Much of that research will be pursued with the technologies of molecular biology and genetics. This review concerns how such technologies might be used to advance our capacities to enhance beneficial influences and minimize harmful effects of the biota.

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During the hundreds of thousands of years that bacteria have co-existed with humans, they have developed highly specialised skills to maintain stable niches in the gastrointestinal tract. To achieve this they act in concert with their hosts to create a fully integrated ecosystem and facilitate the process by modifying host gene expression and function so that habitats are shaped according to the needs and capabilities of the resident flora. This has a profound influence on the human host, and we are dependent on a functional intestinal microflora for our health. By deciphering the strategies employed by the intestinal microflora to create mutualistic relationships with its host we will gain entirely new insights into the shaping and maintenance of human physiology. The combination of genetically defined model hosts and microorganisms, gnotobiology providing a controlled environment, and high resolution molecular techniques will be important tools in this quest. These insights will provide a more accurate understanding of both functionality as well as of the pathogenesis of a wide array of diseases. Inaddition, it will open up new opportunities for treatment and prevention of disease.

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Bacterial species that have traditionally been regarded as safe are used in probiotics. The main strains used include lactic acid bacteria and bifidobacteria. However, reports of frequent isolation of bacteria used in probiotics from infection sources in recent years have raised much debate over the safety of probiotics. This article describes the status quo of isolation of probiotic bacteria from infections and reviews each of the factors that have to be addressed in assessing the safety of probiotics, namely pathogenicity, infectivity, toxicity, and intrinsic properties of the bacteria. Monoassociation with Bifidobacterium longum BB536 in gnotobiotic mice as a method to assess safety with respect to infection, and translocation and immune responses as a result of the monoassociation are also described.

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The ability of survival of Pediococcus pentosaceus IDS885 strain in the gastrointestinal tract and the effect of ingestion of cultured vegetable drink prepared with 8 kinds of vegetables and Pc. pentosaceus IDS885 on fecal microflora in human were studied. Twelve healthy subjects administrated 100 g of cultured vegetable drink containing 5×10⁸ CFU per gram for 4 weeks. Fresh fecal samples were collected before (day-5), during (day 3, 7, 14, 21, 28) and after ingestion (day 35). Pc. pentosaceus IDS885 was enumerated for all samples and the fecal microflora was analyzed before (day-5) and during ingestion (day 28). Pc. pentosaceus IDS885 strain was not detected before administration of cultured vegetable drink (day-5), but averaged 10⁶∼10⁷CFU per gram for ingestion period (day 3, 7, 14, 21, 28). When subjects stopped administration of cultured vegetable drink, Pc. pentosaceus IDS885 disappeared from all samples (day 35). In eight cases of 12 subjects, percentage of Bifidobacterium in microflora increased by ingestion of cultured vegetable drink. In five subjects whose percentage of Bifidobacterium was less than 15% increased from 10.2±1.5% to 21.7±12.8%, while percentage of Bacteroides decreased from 69.2±12.5% to 59.5±18.3%. From these results, we demonstrated that Pc. pentosaceus IDS885 strain can survive in the human gastrointestinal tract, and administration of cultured vegetable drink altered the composition of fecal microflora in a manner with a beneficial effect for human health.

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