Bacterial Colonization: Bacteria Pili and Adhesins Binding to Host Cell Receptors

Pili enable some organisms to adhere to receptors on target host cells. The pilus has a shaft composed of a protein called pilin. At the end of the shaft is the adhesive tip structure having a shape corresponding to that of specific glycoprotein or glycolipid receptors on a host cell. Because both the bacteria and the host cells have a negative charge, pili may enable the bacteria to bind to host cells without initially having to get close enough to be pushed away by electrostatic repulsion. Once attached to the host cell, the pili can depolymerize and this enables bacterial cell wall adhesins to bind to adhesin receptors on the host cell. This allows the bacterial cell wall to make more intimate contact with the host cell and enables the bacterium to colonize the host cell and resist flushing. There is also evidence that the binding of pili to host cell receptors can serve as a trigger for activating the synthesis of some cell wall adhesins.