INFLUENCE OF PILI, FIBRILS, AND CAPSULE ON IN-VITRO ADHERENCE BY HAEMOPHILUS-INFLUENZAE TYPE-B

Haemophilus influenzae type b is an encapsulated bacterium that initia tes infection by colonizing the upper respiratory epithelium. In vitro studies indicate that H. influenzae type b is capable of expressing t wo morphologically distinct filamentous adhesive structures, referred to as pill and fibrils, respectively, In this study, we examined adher ence to a variety of human epithelial-cell types and demonstrated that pill and fibrils have separate cellular binding specificities. In add ition, we found that capsular material inhibits fibril recognition of the host-cell surface, This inhibitory effect was reduced when bacteri a were grown to stationary phase, reflecting diminished encapsulation, However, when growth medium was supplemented with Mg2+, stationary-ph ase organisms were relatively heavily encapsulated and non-adherent, T hese observations suggest that encapsulation can be modulated in respo nse to growth phase or environmental signals. It is possible that enca psulation is down-modulated early in the infectious process in order t o avoid interfering with colonization. In contrast, encapsulation may be up-modulated between hosts and during bacteremia, where it appears to confer a selective advantage, We speculate that this model may also apply to other encapsulated pathogens.