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. In addition, it will open up new opportunities for treatment and prevention of disease.
Lactobacillus casei Shirota (LcS), a strain of lactic acid bacteria, has been investigated for biological activity over many years. Recently it was revealed that LcS has potent antitumor and antimetastatic effects in rodents: An intrapleural injection of LcS effectively inhibits tumor growth in the thoracic cavity in mice, resulting in prolonged survival and an improved quality of life (QOL). These activities were dependent on the stimulation of the production of several cytokines such as interferon-γ, interleukin-12, and tumor necrosis factor-α. It was suggested that LcS induces a Thl response rather than a Th2 response. As a result of this action, the inhibition of ovalbumin-specific immunoglobulin E production in the LcS-treated group was evident, compared with the response in the control group. Also, an oral administration of LcS significantly delayed the onset of carcinogenesis in mice treated with 3-methylcholanthrene and restored T cell responses such as concanavalin A-induced T cell proliferation and interleukin-2 production. Moreover, it was demonstrated that an oral administration of LcS enhanced the natural killer cell activity of spleen cells. These observations indicate that LcS affects innate immunity and augments the natural resistance of the host. Taken together, the results suggest that LcS has the potential to ameliorate or prevent a variety of diseases through a modulation of the host's immune system, specifically cellular immune responses.
The potential of six strains of Bifidobacterium to colonise the gastrointestinal (GI) tract of Swiss mice, their interaction i n the GI tract of Swiss mice and their in-vitro characteristics were investigated. This study revealed that a strain of Bifidobacterium that was isolated from a C57BL/10 ScSn mouse was capable of colonising the GI tract of Swiss mice and remaining there for at least one month. The in-vitro studies showed that this strain had the highest capability among the six strains to adhere to the intestinal tissue of BALB/c mice. This strain grew in presence of 2% bile and lost less than 10-fold viability at pH 2.5.
The effect of the ingested culture of Propionibacterium freudenreichii ET-3 that produced bifidogenic growth stimulator (BGS) on stool frequency and quantity was investigated in 41 young healthy women in a randomized double-blind crossover study. The fecal samples of 7 of these 41 subjects were analyzed to study the modification of intestinal microflora by BGS. The results were compared with the effects of an ingested placebo tablet. The ratio of bifidobacteria population (%) to total bacteria population during the BGS-tablet intake period was significantly increased (p < 0.05) in comparison with that during the placebo tablet intake period. There were no significant differences in fecal pH and water contentduring the experimental periods. However, the putrefactive metabolites, namely, fecal indole and skatole concentration, of the BGS-tablet intake period significantly decreased (p < 0.05) in comparison with those of the placebo tablet period. The stool quantity of the BGS-tablet intake period was slightly higher (p = 0.083) than that of the nonintake period. Moreover, the stool frequency of the BGS-tablet intake period chosen from those originally with lower frequency (≤ 4 times/week) was significantly higher (p < 0.05) than that of the placebo tablet intake period. These results show that the ingestion of P. freudenreichii ET-3 culture increases the number of defecations of constipated females, indicating an improvement of intestinal microflora.
The effects of the soy protein and casein diets on mice were studied. Bifidobacteria, clostridia, and lactobacilli were fewer and the cecal β-glucuronidase activity was higher in the soy protein diet group. Equol was detected only in plasma from the soy protein diet group. These results indicate that the soy protein diet has an impact on the intestinal microflora.