Associations and physiological interactions of indigenous microorganisms and gastrointestinal epithelia

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Abstract
Some indigenous microorganisms associate intimately with the mucosal epithelia in various areas of the gastrointestinal canals of mammals and birds. Certain microbial types associate with particular epithelia. In dissimilar animal types, similar types of microorganisms can be found on comparable epithelia in the stomach or bowel. Some of the microbial types attach directly to epithelial cells. For instance, certain indigenous lactobacilli attach specifically and directly to keratinized squamous cells in the murine stomach. This particular attachment may be mediated by acid mucopolysaccharides on the surface of bacteria. Other microbial types do not attach directly to cells. These organisms colonize the mucin layered over the epithelium. Examples are a yeast (Torulopsis sp.) that colonizes the secreting epithelium of the murine stomach, and spiral- and fusiform-shaped anaerobic bacteria that colonize the epithelium of the mouse large bowel. Such organisms are undoubtedly components of the autochthonous microbiota in the alimentary canals of animals. Autochthonous microbes interact physiologically in important ways with their animal host. Some such microbes markedly depress alkaline phosphatase activity in the duodena of mice. Physiological interactions with its autochthonous biota must have important consequences for the health and well-being of an animal.