A cute diarrhoea is the main cause of mortality and morbidity. Under normal conditions, the gastro-intestinal mucosa resists aggressions due to its protective blanket of mucus, and membrane of gastric epithelium cells. The mucus produced by the epithelium goblet cells is a continuous physical barrier between the underlying tissue and micro-organisms, the toxins they produce, and the antigens present in the intestinal lumen. Mucus is also a competitive inhibitor for adherence to the epithelial cells.
Adherence is a vital factor in intestinal colonisation.
It is achieved by means of the fimbriae or pili, flagella responsible for mobility, by chemotactic factors and by interactions between the bacteria and mucus. For many bacteria, the specific nature of the interactions is known. On the surface of E. coli , Helicobacter pylori and Yersinia enterocolitica , for example, there are specific proteins called adhesins which often recognise carbohydrates on target cells. Inhibition of an organism's adhesion to the epithelial cells may be due to similarities between its natural binding site and the mucin's carbohydrates. The protein core of mucins may also contain hydrophobic zones able to form non-covalent bonds with lipids which would protect certain potential receptors from bacteria.