The human gut harbors a complex and diverse microbiota. The numbers of microorganisms in the upper gastrointestinal (GI) tract are kept low by the actions of gastric acid, pancreatic enzymes, bile, and a propulsive motor pattern. The colonic population of microbes is estimated to be 1012 organisms/gram with at least 400 possible species. The above figure was obtained by traditional culture-based methods. Modern molecular methods such as 16S ribosomal RNA clone libraries that are discussed in Chapter 1 indicate that the number of species will be even higher. The composition of the intestinal microbiota varies from human to human. These differences in the composition of the microbiota are affected by physiological, chemical, and environmental factors. The common intestinal microbiota in humans includes predominantly members of genera Clostridium, Eubacterium, Bacter-oides, Atopobium and Bifidobacterium spp. and many others to a lesser extent. There is an approximation that almost 90% of the cells in our body are microbial, whereas only 10% are human.

The bacteria that colonize the gut must be able to proliferate at a rate that resists washout. Adherence to the intestinal mucosal surface is an important factor in intestinal bacterial colonization. In healthy individuals, a layer of mucus is found to line the gut. It is composed mostly of glycoproteins and serves as a lubricant and a protective lining over the mucosa. Microbiota degradation of the mucin polymeric glycoprotein results in the release of monosaccharides such as N-acetylglucosamine and fucose amongst others, which the microbiota use to support their growth (2). Furthermore, under the mucus the surfaces of intestinal epithelial cells are covered with an abundance of terminally fucosylated glycoproteins and glycolipids which are induced by members of the intestinal microbiota (3). In particular, it was demonstrated that Bacteroides thetaiotaomicron cleaves L-fucose moieties from the host's surface and internalizes them for use as an energy source. This commensal microbe modulates the production of the fucose by the host with its requirement needs, which gives it a competitive colonization advantage within the intestinal niche (68). Thus, the interaction of microorganisms with the mucosa is a complex one, which involves cross-talk between the microbes, and between the microbes and the host.

In this chapter, we provide some insights about the development and regulation of the gastrointestinal microbiota as well as the interaction of the microbes with the intestinal mucosal layer. The majority of research on the molecular interactions between microbes and the mucosa relate to pathogen-enterocyte interaction, and consequently, this field is also occasionally referred to.

Pregnancy And Childbirth

Pregnancy And Childbirth

If Pregnancy Is Something That Frightens You, It's Time To Convert Your Fear Into Joy. Ready To Give Birth To A Child? Is The New Status Hitting Your State Of Mind? Are You Still Scared To Undergo All The Pain That Your Best Friend Underwent Just A Few Days Back? Not Convinced With The Answers Given By The Experts?

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