Influence of Pili, Fibrils, and Capsule on in Vitro Adherence by Haemophilus Influenzae Type B

Mol Microbiol. 1996 Jul;21(1):21-31. doi: 10.1046/j.1365-2958.1996.6241331.x.


Haemophilus influenzae type b is an encapsulated bacterium that initiates infection by colonizing the upper respiratory epithelium. In vitro studies indicate that H. influenzae type b is capable of expressing two morphologically distinct filamentous adhesive structures, referred to as pili and fibrils, respectively. In this study, we examined adherence to a variety of human epithelial-cell types and demonstrated that pili and fibrils have separate cellular binding specificities. In addition, we found that capsular material inhibits fibril recognition of the host-cell surface. This inhibitory effect was reduced when bacteria were grown to stationary phase, reflecting diminished encapsulation. However, when growth medium was supplemented with Mg2+, stationary-phase organisms were relatively heavily encapsulated and non-adherent. These observations suggest that encapsulation can be modulated in response to growth phase or environmental signals. It is possible that encapsulation is down-modulated early in the infectious process in order to 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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Bacterial Adhesion / drug effects
  • Bacterial Adhesion / physiology*
  • Cell Line
  • Fimbriae, Bacterial / physiology*
  • Haemophilus Infections / etiology
  • Haemophilus influenzae / growth & development
  • Haemophilus influenzae / pathogenicity*
  • Haemophilus influenzae / physiology*
  • Humans
  • In Vitro Techniques
  • Magnesium / pharmacology
  • Models, Biological
  • Mutation
  • Polysaccharides, Bacterial / genetics
  • Polysaccharides, Bacterial / physiology
  • Virulence / drug effects
  • Virulence / physiology


  • Polysaccharides, Bacterial
  • Magnesium