Jw. Stgeme et D. Cutter, INFLUENCE OF PILI, FIBRILS, AND CAPSULE ON IN-VITRO ADHERENCE BY HAEMOPHILUS-INFLUENZAE TYPE-B, Molecular microbiology, 21(1), 1996, pp. 21-31
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.