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Background Bifidobacterium longum 105-A produces markedly high amounts of capsular polysaccharides (CPS) and exopolysaccharides (EPS) that should play distinct roles in bacterial–host interactions. To identify the biological function of B. longum 105-A CPS/EPS, we carried out an informatics survey of the genome and identified the EPS-encoding genetic locus of B. longum 105-A that is responsible for the production of CPS/EPS. The role of CPS/EPS in the adaptation to gut tract environment and bacteria-gut cell interactions was investigated using the ΔcpsD mutant.ResultsA putative B. longum 105-A CPS/EPS gene cluster was shown to consist of 24 putative genes encoding a priming glycosyltransferase (cpsD), 7 glycosyltransferases, 4 CPS/EPS synthesis machinery proteins, and 3 dTDP-L-rhamnose synthesis enzymes. These enzymes should form a complex system that is involved in the biogenesis of CPS and/or EPS. To confirm this, we constructed a knockout mutant (ΔcpsD) by a double cross-over homologous recombination. Compared to wild-type, the ∆cpsD mutant showed a similar growth rate. However, it showed quicker sedimentation and formation of cell clusters in liquid culture. EPS was secreted by the ∆cpsD mutant, but had altered monosaccharide composition and molecular weight. Comparison of the morphology of B. longum 105-A wild-type and ∆cpsD by negative staining in light and electron microscopy revealed that the formation of fimbriae is drastically enhanced in the ∆cpsD mutant while the B. longum 105-A wild-type was coated by a thick capsule. The fimbriae expression in the ∆cpsD was closely associated with the disappearance of the CPS layer. The wild-type showed low pH tolerance, adaptation, and bile salt tolerance, but the ∆cpsD mutant had lost this survivability in gastric and duodenal environments. The ∆cpsD mutant was extensively able to bind to the human colon carcinoma Caco-2 cell line and was phagocytosed by murine macrophage RAW 264.7, whereas the wild-type did not bind to epithelial cells and totally resisted internalization by macrophages.ConclusionsOur results suggest that CPS/EPS production and fimbriae formation are negatively correlated and play key roles in the survival, attachment, and colonization of B. longum 105-A in the gut.Electronic supplementary materialThe online version of this article (doi:10.1186/s13099-017-0177-x) contains supplementary material, which is available to authorized users.

Bovine colostrum is a rich source of tissue repair and growth factors, and inhibits gastrointestinal injury induced by the side effects of nonsteroidal antiinflammatory drugs (NSAID), such as indomethacin. Nonsteroidal antiinflammatory drugs are drugs with analgesic and antipyretic effects, but in higher doses they have inflammatory effects. The pathogenesis of small intestinal damage caused by NSAID is unclear. The present study was performed to investigate the antiinflammatory effects of skimmed, sterilized, and concentrated bovine late colostrum on intestinal injury induced by side effects of NSAID, and then to identify the active ingredient in the colostrum for intestinal tissue. In Japan, the sale of bovine colostrum within 5 d after parturition is prohibited by law. Therefore, we focused on bovine late colostrum obtained from healthy lactating cows 6 to 7 d after parturition. Proliferation of small intestine epithelial cells was stimulated in mice fed the colostrum for 1 wk. With regard to indomethacin-induced enteropathy, both prefeeding and postfeeding with colostrum facilitated growth of the intestinal villi, indicating preventive and healing effects. Furthermore, to identify the active ingredient in the colostrum responsible for this effect, the casein and whey fractions were prepared from the colostrum and fed to normal mice. Only the colostrum casein fraction stimulated intestinal villus elongation, whereas the whey fraction and mature milk casein showed no such effect. Taken together, these observations indicate that the skimmed, sterilized, and concentrated bovine late colostrum, especially the casein fraction, could be used to treat the injurious effects of NSAID in the intestine and could be effective for treatment of other ulcerative conditions in the bowel, suggesting that the colostrum has therapeutic potential for intestinal inflammation.

We found that skimmed and concentrated bovine late colostrum (SCBLC) obtained from normal cows at 6-7 d after parturition exhibited high potency in inhibiting replication of human rotavirus (HRV) in vitro. Furthermore, prophylactic oral administration of SCBLC once before inoculation of HRV prevented the development of diarrhea in suckling mice in vivo. SCBLC from normal cows might be useful in the prevention of HRV-induced severe gastroenteritis in immunocompromised hosts.

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