Cellular and molecular mechanisms of bacterial adhesion to respiratory mucosa

Different bacterial species adhere avidly to respiratory mucus. Such adhesion, when followed by ciliary clearance, represents an important stage of the airway defense system. However, in pathological conditions, the mucociliary clearance may be severely reduced, and mucus-associated bacteria may multiply and infect the underlying epithelium. Only a few bacteria have been shown to adhere to ciliary membranes of functionally active ciliated cells. Therefore, the first way in which most of the respiratory pathogens associate with the airway epithelium is likely to be by their adhesion to mucus. Some bacteria also secrete products that may affect ciliary function and/or cause cell death and epithelial disruption. Respiratory pathogens that do not bind to normal ciliated cells may readily adhere to injured epithelial cells, or to the unmasked extracellular matrix. Furthermore, following injury, epithelial respiratory cells in the process of migration, in order to repair the wounds, may present receptors to which bacteria adhere. The adhesion to all of these epithelial receptors may contribute to the chronicity of many bacterial respiratory infections.