Until recently, ecological analysis of human intestinal microbiota had been conducted with culture-dependent methods. However, the majority of our intestinal bacteria remain not-yet cultured. Many culture-independent, molecular ecological methods have been developed to investigate real compositions of microbiota in the last decade. Among them, fluorescencein situhybridization (FISH) is one of the most widely used methods, though it is time-consuming and requires laborious counting work of the detected bacteria. Development of FISH coupled with flow cytometry (FISH-FCM) has circumvented this problem. Since the development of FISH-FCM, it has been used in several fields of microbiology such as environmental microbiology and clinical microbiology. It is now being applied to more complex biological samples, such as feces. These days, intestinal microbiota analyses with FISH-FCM are being conducted not only at group or genus level, but also at the species level. Recently, we have succeeded in the development of a FISH-FCM method that is applicable to fecal samples containing high amounts of autofluorescent particles. Further development of specific probes for the bacteria of interest will contribute to the illustration of the real picture of our intestinal microbiota

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Probiotics have beneficial effects on the host health. These effects are mediated through the improvement of intestinal microflora to increase the number of health-promoting bacteria and to stimulate colonic fermentation. Ingested probiotic bacteria competitively and/or symbiotically interact with indigenous intestinal bacteria. This interaction can lead to improvement in the intestinal microflora and colonic environment. The succession of intestinal microflora is affected by many factors. As a result, every individual has a unique intestinal microflora. Individual differences in intestinal microflora may induce inter-individual differences of probiotic effects, because the interaction between intestinal microflora and probiotic bacteria can differ from one individual to another. The composition of intestinal microflora is one of the important factors determining the efficiency of probiotics.

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The role of tannase produced by Lactobacillus plantarum in tannin-rich medium was demonstrated by using strains with known tannase activities. After 20 h incubation in aerobic tannin-rich medium, the growth of L. plantarum KOG 19 with low activity was lower than that of L. plantarum ATCC 14917^T with high activity by approximately 1.5 orders of magnitude, whereas the growth of KOG 19 in aerobic medium without tannin was almost the same as that of ATCC 14917^T. The reduced growth of KOG 19 in aerobic tannin-rich medium was recovered by the addition of exogenous tannase or Mn²⁺ to the medium. A similar result was obtained in the comparison of growth levels between high and low tannase activity groups in aerobic tannin-rich medium, while no significant differences were observed between the groups in anaerobic tannin-rich medium. Furthermore, the growth of the low tannase activity group in aerobic tannin-rich medium was restored by the addition of catalase. These results suggest that tannase production allows L. plantarum strains to acquire and accumulate Mn²⁺ which is otherwise chelated by tannins, and then high intracellular Mn²⁺ compensates for the lack of the enzyme superoxide dismutase in L. plantarum resulting in resistance to oxygen toxicity under aerobic conditions.

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This study examined the effect of Lactobacillus plantarum ONRIC b 0240 (L.p.b 0240) on the amounts of salivary and fecal IgA in adult volunteers. A double-blind comparative study was conducted on healthy adult volunteers. Thirty subjects were randomly divided into three groups, control group, L.p.b 0240 (2x10⁹ CFU) group and L.p.b 0240 (2x10⁹ CFU) group, and their diets were supplemented for 3 weeks. Twenty-six subjects completed the study. The results show the salivary IgA secretion rate was significantly higher for the L.p.b 0240 group than that of the control group. Furthermore, the amount of fecal IgA was higher in the L.p.b 0240 group than that of the control group, but not significantly. In addition, no adverse reaction was observed after oral administration of L.p.b 0240 during the study. These results suggest that L.p.b 0240 may con- tribute to the host defense through the enhancement of the mucosal immune function.

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