Haemophilus influenzae adheres to and enters cultured human epithelial cells

Haemophilus influenzae is a common commensal organism of the human respiratory tract that initiates infection by colonizing the nasopharyngeal epithelium. In some individuals, colonization is followed by localized respiratory tract or systemic disease. To gain insight into the mechanisms by which H. influenzae attaches to and persists within the nasopharynx, we examined the interactions between a nonpiliated clinical isolate of H. influenzae and human epithelial cells. We noted substantial adherence that occurred independently of pili and required viable bacteria capable of de novo protein synthesis. Comparison of profiles of outer membrane proteins synthesized during incubation with epithelial cells for adherent and nonadherent bacteria identified several candidate adhesin molecules. In addition, a small number of adherent bacteria were capable of entering epithelial cells in a process that was inhibited by cytochalasin D and colchicine. The suggestion from our studies is that one or more of several newly synthesized nonpilus bacterial proteins are required for maximal in vitro adherence and invasion. We speculate that H. influenzae entry into epithelial cells may provide a mechanism for evasion of host defenses, thereby allowing persistence in the nasopharynx.