Mucin in the GI tract is produced by goblet cells in the mucosa and glandular mucous cells in the submucosa. Mucin consists of a peptide core with oligosaccharide side chains O-glycosidically bound, and it has several important physiological and patho-physiological roles. It acts as lubricant, as a barrier and stabilizer for the intestinal microclimate as well as a source of energy for the microbiota. There is growing evidence that the mucin pattern may be a relevant issue to take into account in the pathophysiology of some intestinal diseases, such as ulcerative colitis, Crohn's disease, gastric and duodenal ulceration, and colon adenocarcinoma.
In contrast to conventional rats and healthy adult humans, organisms without any intestinal microbiota excrete large amounts of mucin with their feces (28). The complete degradation of mucin requires various glycosidases and peptidases, and the degradation is a sequential action of several bacterial strains (28,29). However, one Peptostreptococcus strain can degrade mucin in vitro and in vivo (30). Additionally, some strains belonging to other species can act upon mucin (31) e.g., Bifidobacterium and Ruminococcus genera (31) have been isolated and are related to degrading of mucin.
In all mammalian species so far studied, the intestinal microbiota is capable of breaking down mucin (8). In healthy children the function is successively established within the first year of life. It has also been shown that the microbiota might act upon the glycosylation pattern of mucin (32). In fact, alteration in glycosylation was the first observation of a molecular, quorum sensing dependent cross-talk between a host and a single microbial strain present in the GI tract (33). Also regarding this intestinal function, it has been demonstrated that different antibiotics cause disturbance of this microbial function in animals and man (34,35).
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