Pathogens usually colonize host tissues that are in contact with the external environment.
Sites of entry in human hosts include the urogenital tract, the digestive tract, the respiratory tract and the conjunctiva. Organisms that infect these regions have usually developed tissue adherence mechanisms and some ability to overcome or withstand the constant pressure of the host defenses on the surface. Bacterial Adherence to Mucosal Surfaces. The receptors so far defined are usually specific carbohydrate or peptide residues on the eukaryotic cell surface. The bacterial adhesin is typically a macromolecular component of the bacterial cell surface which interacts with the host cell receptor.