Adherence of Haemophilus influenzae to human buccal and pharyngeal epithelial cells: relationship to pilation.

An improved understanding of the role of pili in adherence of Haemophilus influenzae type b to human epithelial cells (EC) would enhance knowledge of the pathogenesis of H. influenzae b infections. In this study a highly sensitive in-vitro assay allowed the quantitative assessment of H. influenzae b adherence to EC. The degree of adherence was influenced by incubation time, temperature, bacteria/EC ratio, EC type and the growth phase of the bacteria. Most serially subcultured (SC) capsular type-b strains originally isolated from cerebrospinal fluid, blood, nasopharynx or throat gave similar low degrees of adherence, as did representative single strains of capsular types a, c, d, e and f. SC non-capsulated H. influenzae strains adhered in significantly greater numbers than most SC capsulated strains (p less than 0.001). One SC type-b strain isolated from a throat, with stable piliation, adhered in very high numbers despite capsulation. Piliated subpopulations selected from type-b capsulated strains adhered in greater numbers than did their parent strains. These data suggest that capsulation of H. influenzae is a deterrent to adherence of the bacteria to EC. However, the presence of pili may allow type-b organisms to overcome the effects of capsulation.