Fimbria-mediated adherence and hemagglutination of Haemophilus influenzae.

The gram-negative bacterium Haemophilus influenzae expresses morphologically and functionally distinct types of fimbriae, of which the LKP fimbriae mediate hemagglutination and adherence to human epithelial cells but hamper mucosal invasion. Therefore, the both in vivo and in vitro observed fimbrial phase variation may contribute to the pathogenesis of the infection. The existence of greater than 14 LKP serotypes hampers vaccine development based on fimbriae, since a monovalent fimbria vaccine confers protection against only the homologous strain. Cloning of the fimbrial genes in Escherichia coli results in the expression of morphologically intact fimbriae. Analysis of the cloned DNA indicates that a fimbrial gene cluster is necessary for formation of complete fimbriae and for fimbria-mediated adherence. The gene encoding the subunit is highly conserved among H. influenzae and belongs to the family of E. coli fimbriae. The phase variation is transcriptionally regulated by variation of the length of the reiterated sequence that forms the promoter region of the subunit gene.