Gut microbes are present in large concentrations on the human intestinal mucosal surface and play important roles in health and disease of the host. Numerous groups of gut microbes are associated with immunological and metabolic diseases and in maintaining health status of the host. Among these health- and disease-associated gut microbes, Bacteroides, Clostridium and Bifidobacterium appear regularly in the list. Scientific and clinical evidence available to date indicates that diet is a major driving factor for the establishment of the gut microbiome. Slow digestible carbohydrates (human milk glycan, inulin and fructooligosaccharide), insoluble complex carbohydrates and protein diets favor the growth of Bacteroides, Clostridium and Bifidobacterium. Fat on the other hand suppresses the number of Bacteroides, Clostridium and Bifidobacterium; whereas polyphenols in general suppress Bacteroides and Clodtridium but enhance the Bifodobacterium. The implication is that dietary habits could be a major determinant of health and disease susceptibility. Dietary strategies could be an effective means of potentially inducing changes in intestinal microbiota and are certainly achievable, thus facilitating correction of intestinal microbiome aberrations or imbalances to improve our health. Most of the physiological and functional interactions between individual dietary components and the concoction of foods in a meal and gut microbiota have not yet been well studied. A concerted effort is required to acquire better understanding of their interaction in order to rationally maintain our intestinal microbiome homeostasis and general health through dietary intervention.

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The effects of oral administration of enteric-coated tablets containing lactoferrin (LF; 100 mg/tablet) and heat-killed Lactobacillus brevis subsp. coagulans FREM BP-4693 (LB; 6×10⁹ bacteria/tablet) on fecal properties were examined in 32 Japanese women (20–60 years of age) with a tendency for constipation (defecation frequency at equal to or less than 10 times/2 weeks) by a double-blind placebo-controlled crossover design. A significant increase in defecation days per week was obserbed in the subjects who ingested the tablets containing LF and LB compared with the placebo group. The number of bifidobacteria in feces also significantly increased compared with the placebo group. In an in vitro study, LF and tryptic hydrolysate of LF, but not peptic hydrolysate of LF, upregulated the growth of Bifidobacterium longum ATCC15707 when added to the culture. These results demonstrate the capability of the enteric-coated tablets containing LF and LB in improving intestinal function and suggest that they have a growth promoting function for bifidobacteria.

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In yogurt, the formation of formate by Streptococcus thermophilus stimulates the activity of Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). However, there have been no reports how formic acid acts on the exopolysaccharide (EPS) production of L. bulgaricus. Here, the effect of formate on the EPS production in skim milk by L. bulgaricus OLL1073R-1 was investigated. After incubation for 24 hr with 100 mg/l formate, cell proliferation and lactic acid production were accelerated. The viable and total cell numbers were increased about ten- and four-fold, respectively. The amount of EPS in culture with formate (~116 µg/ml) was also four-fold greater than that of the control (~27 µg/ml). Although elongation of cells was observed at 6 hr of cultivation in both cultures, cells cultivated with formate returned to a normal shape after incubation for 24 hr. The sensitivity to cell wall hydrolase and composition of surface layer proteins, as well as the cell membrane fatty acid composition of L. bulgaricus OLL1073R-1, were not influenced by formate. However, differences were observed in intracellular fatty acid compositions and sensitivity to antibiotics. Cell length and surface damage returned to normal in cultures with formate. These observations suggest that formic acid is necessary for normal cell growth of L. bulgaricus OLL1073R-1 and higher EPS production.

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A double-blind, placebo-controlled, randomized trial was conducted to investigate the beneficial effect of probiotic and prebiotic fermented milk on the skin of healthy adult women. Forty healthy Japanese adult female volunteers with healthy skin randomly received either a bottle of probiotic and prebiotic fermented milk containing Bifidobacterium breve strain Yakult and galacto-oligosaccharides (GOS) (active group) or a non-fermented placebo milk containing neither probiotics nor GOS (placebo group) daily for 4 weeks. Before and after intake, hydration levels and cathepsin L-like activity in the stratum corneum and phenol levels in the serum and urine were determined. After intake, the hydration level of the stratum corneum decreased significantly in only the placebo group and was significantly lower than in the active group (p=0.031). Cathepsin L-like activity, an indicator of keratinocyte differentiation, was significantly increased in the active group (p=0.027). Serum and urine phenol levels decreased significantly in the active group (p=0.014, p=0.002, respectively), and serum phenol levels were significantly lower in the active group compared with the placebo group (p=0.006). The consecutive intake of probiotic and prebiotic fermented milk can benefit skin condition without dryness and decrease the levels of phenol production by gut bacteria in healthy adult women.

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