Bile acid stress is one of the most powerful gastrointestinal stresses for probiotic lactic acid bacteria and bifidobacteria. Recent analysis using functional genomics is beginning to unravel whole picture of stress response in these bacteria upon challenge by bile acid. In this review article, the bile acid stress responses in these bacteria are overviewed in special reference to those to prevent deleterious actions of bile acid on bacterial cell membrane.

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Quorum sensing is a cell-density dependent regulatory system which is sometimes involved in expression of pathogenicity-related genes. Gram-positive bacteria often employ peptidic compound as an autoinducer to control quorum sensing and the peptide-mediated quorum sensing has attracted interest as a new target of antipathogenic agents. In this review, current knowledge and future scope for the development of quorum sensing inhibitors will be presented.

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Lactobacillus casei YIT 9029 (Shirota strain), a popular strain of probiotics, can survive within the intestine, affect the intestinal microflora and produce metabolites, resulting in the regulation of intestinal functions. This probiotic strain also modulates the host immune system and exerts health benefits. L. casei YIT 9029 is one of the pioneer strains for the application in controlling allergy, in addition to reducing a cancer risk and restoring NK cell activity. This review outlines a series of studies showing that the improvement of Th1/Th2 balance is one of the critical anti-allergic mechanism of probiotics, and also describes the clinical effects of L. casei YIT 9029-containing fermented milk in patients with pollen allergy.

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The ‘hygiene hypothesis’, which postulates that decreased opportunities for exposure to immunostimulating pathogens in early childhood has been proposed for the explanation of the rapidly increased prevalence of allergic diseases over the past decades. It has been suggested that association of allergy development with intestinal microflora, and probiotic bacteria have been demonstrated to be effective in the treatment of allergic disorders. Bifidobacterium longum BB536, a probiotic strain originated from a healthy infant, has been shown to be efficient in the treatment of Japanese cedar pollinosis (JCPsis)in several clinical trials. It has been reported that bifidobacteria would exhibit anti-allergic effects by modulating Th1/ Th2 balance and inducing regulatory T cells. Furthermore, in the clinical trials on JCPsis, BB536 suppressed the fluctuation along with pollen dispersion of Bacteroides fragilis group in fecal microbiota of JCPsis subjects, suggesting an indirect mechanism of BB536 by the maintenance of normal microbiota. In this review, we would introduce some data concerning the anti-allergic effects and the mechanisms of bifidobacteria with focus on the results of the efficacy of BB536 in the treatment of JCPsis.

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[in Japanese]

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