Influence of pili, fibrils, and capsule on in vitro adherence by Haemophilus influenzae type b.
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.
St Geme
J W
JW
Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, St. Louis, Missouri 63110, USA. stgeme@borcim.wustl.edu
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D001422:Bacterial Adhesion / Q000187:drug effects / Q000502:physiology*; D002460:Cell Line; D010861:Fimbriae, Bacterial / Q000502:physiology*; D006192:Haemophilus Infections / Q000209:etiology; D006193:Haemophilus influenzae / Q000254:growth & development / Q000472:pathogenicity* / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008954:Models, Biological; D009154:Mutation; D011135:Polysaccharides, Bacterial / Q000235:genetics / Q000502:physiology; D014774:Virulence / Q000187:drug effects / Q000502:physiology
D011135:Polysaccharides, Bacterial; D008274:Magnesium