Adherence kinetics of Haemophilus influenzae type b to eucaryotic cells

Haemophilus influenzae type b (Hib) adhere in vitro to buccal epithelial cells (BEC) via pili (fimbriae). In vivo studies have conflicting lines of evidence concerning the role of pili in adherence. This study characterizes the kinetics of Hib binding to BEC and compares pilus versus nonpilus adherence. Adherence was assessed using radioactive, immunofluorescence, and electron microscopic techniques. Paired Hib strains were obtained from three children with Hib meningitis; piliated Hib were isolated from the nasopharynx and nonpiliated isolates from the cerebrospinal fluid. Piliated strains adhered avidly to BEC after a 1-h incubation, whereas nonpiliated strains adhered poorly (p = 0.002). Kinetic analysis revealed increased adherence to BEC by piliated and nonpiliated strains with time, with maximum adherence occurring between 24-36 h. Immunofluorescence and electron microscopic assays visually confirmed the radioactive adherence findings. These results characterize the kinetics of Hib adherence to BEC. BEC incubated with nonpiliated Hib for 30 h were found to be coated with piliated strains, suggesting the induction of pilus production or the selection of a piliated subpopulation.