Adherence and invasion of Haemophilus influenzae

Adherence of Haemophilus influenzae to epithelial cells plays a central role in colonization and is the first step in infection. It allows H. influenzae to establish itself, adapt to local conditions required for localized growth of the bacteria, and resist mechanical clearance mechanisms of the host. Bound to the cells the organism can evoke localized effects on the tissue which may lead to an inflammatory reaction, or the penetration of the bacteria between the cells into the tissues underlying the epithelium. Various adhesins, including fimbriae and high-molecular-weight outer membrane proteins, promote binding to different receptors, resulting in tissue tropism. A variety of other bacterial determinants, including the capsule and LPS, also contribute to the establishment and course of the infection. The occurrence of random and reversible fimbrial phase variation ensures the generation of a genetically and phenotypically diverse bacterial population. The diversity allows properly equipped H. influenzae cells (fimbriated on epithelia and non-fimbriated in the blood) to be present at random in the bacterial population, not selected for a particular fimbrial phenotype. Subsequently, natural conditions will drive selection of a particular phenotype required for survival in a spedfic host tissue site (mucosa, blood, etc).