CHARACTERIZATION OF THE GENETIC-LOCUS ENCODING HAEMOPHILUS-INFLUENZAETYPE-B SURFACE FIBRILS

Haemophilus influenzae is a common gram-negative pathogen that initiat es infection by colonizing the upper respiratory tract epithelium. In previous work, we reported the isolation of a locus involved in expres sion of short, thin surface fibrils by H. influenzae type b and presen ted evidence that surface fibrils promote attachment to human epitheli al cells. In the present study, we determined that the fibril locus is composed of one long open reading frame, designated hsf, which encode s a protein (Hsf) with a molecular mass of similar to 240 kDa. The der ived amino acid sequence of the hsf product demonstrated 81% similarit y and 72% identity to a recently identified nontypeable H. influence a dhesin referred to as Hia. In experiments with a panel of eight cultur ed cell lines, the Hsf and Hia proteins were found to confer the same binding specificities, suggesting that hsf and hia are alleles of the same locus. Southern analysis and mutagenesis studies reinforced this conclusion, Further investigation revealed that an hsf homolog is ubiq uitous among encapsulated H, influenzae strains and is present in a su bset of nontypeable Haemophilus strains as well, We speculate that the hsf gene product plays an important role in the process of respirator y tract colonization by H. influenzae.