The resident microbiota of the mammalian intestine influences diverse homeostatic functions of the gut, including regulation of cellular growth, restitution after injury, maintenance of barrier function, and modulation of immune responses. However, it is unknown how commensal prokaryotic organisms mechanistically influence eukaryotic signaling networks. We have shown that epithelia contacted by enteric commensal bacteria in vitro and in vivo rapidly generate reactive oxygen species (ROS), and distinct microbial taxa have markedly different potencies in stimulating this response. This physiologically generated ROS is known to participate in a variety of cellular signal pathways via the rapid and transient oxidative inactivation of a number of regulatory enzymes. We show that these oxidant sensitive enzymes include key control points in the proinflammatory NF-κB pathway and in the regulation of cytoskeletal dynamics. Accordingly, we show various commensal bacterial have the ability to suppress inflammatory signaling and stimulate cell motility both in cell culture and in animal models. These events are consistent with known effects of the microbiota and selected probiotics. Collectively, our studies outline a molecular mechanism that may account for aspects of microbial-host cross-talk in the intestine in normal physiology and during therapeutic intervention with probiotics.
Shiga toxin-producing Escherichia coli and Salmonella, causative bacteria of food poisoning (intestinal infectious disease) in humans, are still serious problems. Shiga toxin-producing E. coli O157:H7 (STEC) grows and produces Shiga toxin (Stx) in the intestine, and causes hemorrhagic enteritis. A typical etiologic agent of Salmonella food poisoning, Salmonella enterica serovar Typhimurium (S. Typhimurium), grows in the intestine and invades the body via the intestinal epithelium, causing inflammation. The importance of the prevention of STEC- and S. Typhimurium-induced food poisoning has been stressed because they frequently cause outbreaks, the course is rapid, and only a very small number of bacteria (101 to 103 CFU) is needed to induce a severe infection. Probiotics are defined as `Live microorganisms which when administered in adequate amounts confer a health benefit on the host'. Bifidobacteria, major constituents of the intestinal flora, are typical probiotics which are expected to help prevent intestinal infection. In this study, we investigated the anti-infectious activity of bifidobacteria against STEC and S. Typhimurium infections using a mouse intestinal infection model, and analyzed the infection-preventive mechanism. For STEC infection, a novel mouse fatal infection model was prepared by combining STEC infection at 5 × 10 3 CFU and Mitomycin C (MMC) treatment (for the induction of stx gene expression) in the late logarithmic phase of intestinal STEC growth. The anti-infectious activity of the orally administered probiotic Bifidobcterium breve strain Yakult (BbY) was investigated using this mouse intestinal STEC infection model. STEC-induced death was strongly inhibited in BbY-treated mice. Interestingly, STEC growth in the intestine was not inhibited, but stx gene expression and Stx production were strongly inhibited. In addition, the intestinal environment was improved in the BbY-treated mice through normalization of the intestinal level of acetic acid, a major organic acid in the intestine, and pH. When STEC was grown in vitro in a medium reproducing the acetic acid level and pH in the cecum, Stx production was completely inhibited, suggesting that the expression of this pathogenic factor was inhibited by BbY-induced improvement of the intestinal environment. In the mouse intestinal S. Typhimurium infection model, BbY inhibited the abnormal growth of S. Typhimurium and improved the intestinal environment, resulting in the inhibition of systemic S. Typhimurium infection. This study, using an experimental animal model, clarified the preventive effect of the probiotic BbY on food poisoning (intestinal infectious disease) caused by STEC and S. Typhimurium. Improvements of the intestinal environment, such as elevation of the acetic acid concentration and decrease in pH level, induced by intestinal BbY colonization, are suggested to be important defense mechanisms for the inhibition of pathogenic factors production induce by intestinal STEC and retardation of intestinal S. Typhimurium growth. These findings suggest the usefulness of probiotics as a novel preventive agent for human food poisoning (intestinal infectious disease).
Many bifidobacteria produce an endo-α- N-acetylgalactosaminidase that liberates the O-linked galactosyl β-1,3N-acetylgalactosamine (GNB) from intestinal mucin glycoproteins. The molecular cloning of the Bifidobacteriumlongum enzyme was completed using information in public databases. The enzyme constitutes a novel glycoside hydrolase (GH) family 101 member. The gene encoding a specific 1,2-α -L-fucosidase was cloned from B.bifidum. The recombinant enzyme specifically hydrolyzes the terminal α-1,2-fucosidic linkages of various oligosaccharides, including human milk oligosaccharides and blood group substances. Analysis of its primary structure revealed that this enzyme constitutes a novel GH family 95 member. We also solved the crystal structure of its catalytic domain. We assumed that these bifidobacterial enzymes are involved in the metabolism of oligosaccharides in mucin glycoproteins that are abundant in the intestine. Some bifidobacteria strains produce a lacto-N-biosidase that releases galactosyl β-1,3N-acetylglucosamine (LNB) from human milk oligosaccharides, but the other enteric bacteria do not. This disaccharide is one of the building blocks in human milk oligosaccharides and is rarely found in other mammalian milks. The lacto-N-biosidase gene was cloned from B.bifidum and we hypothesized that this enzyme is crucially involved in the degradation of human milk oligosaccharides. The genes encoding sialidase and α-1,3/4-L-fucosidase were also cloned from B.bifidum. These enzymes release modified sialic acid and L-fucose from human milk oligosaccharides, respectively. A solute-binding protein of a putative ABC transporter specific for GNB and LNB was also discovered, and its gene was cloned from B.longum. We named it GNB/LNB-binding protein and crystallized it. Isothermal titration calorimetry measurements revealed that this protein specifically binds GNB and LNB. We speculate that bifidobacteria have a novel GNB/LNB metabolic pathway.
Short chain fatty acids (SCFAs) are major anions in the large intestine. They are produced by bacterial fermentation of dietary fiber. However, the mechanism by which intraluminal SCFAs are sensed is unknown. Free fatty acids including SCFAs have recently been demonstrated to act as ligands for several G-protein-coupled receptors (GPCRs: FFA1, FFA2, FFA3, GPR84, GPR109A and GPR120). SCFAs are ligands for FFA2 and FFA3. These receptors are proposed to play a variety of physiological and pathophysiological roles in the intestine. In rat and human colons, FFA2 and/or FFA3 are located in mucosal enteroendocrine cells containing peptide YY (PYY) and are related to energy balance. Among SCFAs, propionate and butyrate induce concentration-dependent phasic and tonic contractions in rat colonic circular muscle. These responses are not observed in mucosal free preparations. Thus, FFA2 and FFA3 are important molecular devices for monitoring the chemical composition in the colonic lumen. For the local function of SCFAs, it should be stressed that individual SCFAs have different modes of action on colonic smooth muscles. These different actions may be due to the relative contributions of FFA2 and FFA3 to the control of intestinal muscle activity. FFA2 and FFA3 may also contribute to the whole body energy balance through the release of gastrointestinal hormones related to feeding and satiety control. This review summarizes recent findings about the roles of deorphanized FFA receptors, especially, FFA2 and FFA3 and their contributions to the regulation of colonic motility.
The influence of Prebio SupportTM (PS), which is a mixture of fermented products of Lactobacillus gasseri OLL2716 and Propionibacteriumfreudenreichii ET-3, on the fecal microbiota and fecal metabolites in calves were investigated. During the intake of PS, the number of bifidobacteria was significantly higher (p<0.05), and the fecal water content (p<0.05) and fecal ammonia (p<0.05) were significantly lower in the PS intake group than in the control group. Furthermore, fecal concentrations of sulfide tended to decrease and short-chain fatty acids (acetic, butyric, and propionic acids) tended to increase through the intake of PS. The numbers of other fecal bacteria and the fecal pH of the PS intake group did not differ from those of the control group. The fecal condition, such as hardness, in calves given PS was better than that of the control group. These findings indicate that PS intake effectively improves the fecal environment, and there is a possibility of it alleviating clinical symptoms.
We collected fecal samples twice from 8 subjects and obtained 160 isolates of lactobacilli. The isolates were genetically fingerprinted and identified by pulsed-field gel electrophoresis (PFGE) and 16S rDNA sequence analysis, respectively. The numbers of lactobacilli detected in fecal samples varied greatly among the subjects. The isolates were divided into 37 strains by PFGE. No common strain was detected in the feces of different subjects. Except for one subject, at least one strain, unique to each individual, was detected in both fecal samples. The strains detected in both fecal samples were identified as Lactobacillus amylovorus, L. gasseri, L. fermentum, L. delbrueckii, L. crispatus, L. vaginalis and L. ruminis. They may be the indigenous Lactobacillus species in Japanese adults.