Do pili play a role in pathogenicity of Haemophilus influenzae type B?

Surface components of Haemophilus influenzae type b (Hib) responsible for mucosal adherence were identified through assay of in-vitro attachment to human buccal epithelial cells (EC). Among many Hib strains from cerebrospinal fluid, blood, or the nasopharynx (NP), two isolates from NP were found to be exceptionally adherent. Adherence correlated with agglutination of human red blood cells (RBC). The adherent strains displayed pili, not previously described for Hib or other encapsulated H. influenzae. Moreover, highly adherent, piliated subpopulations of bacteria could be selected from any strain, but were lost upon subculture. Thus, the potential to express pili may be general for Hib and may aid the NP colonisation which precedes systemic invasion by this organism. Piliation was correlated with the amount of an outer membrane protein with a molecular weight of about 20,000 daltons, which had proved to be immunogenic in an 8-month-old child.