Nontypeable Haemophilus influenzae: understanding virulence and commensal behavior

Trends Microbiol. 2007 Aug;15(8):355-62. doi: 10.1016/j.tim.2007.06.004. Epub 2007 Jun 27.


Haemophilus influenzae is genetically diverse and exists as a near-ubiquitous human commensal or as a pathogen. Invasive type b disease has been almost eliminated in developed countries; however, unencapsulated strains - nontypeable H. influenzae (NTHi) - remain important as causes of respiratory infections. Respiratory tract disease occurs when NTHi adhere to or invade respiratory epithelial cells, initiating one or more of several proinflammatory pathways. Biofilm formation explains many of the observations seen in chronic otitis media and chronic bronchitis. However, NTHi biofilms seem to lack a biofilm-specific polysaccharide in the extracellular matrix, a source of controversy regarding their relevance. Successful commensalism requires dampening of the inflammatory response and evasion of host defenses, accomplished in part through phase variation.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Adhesins, Bacterial / metabolism
  • Animals
  • Bacterial Adhesion
  • Biofilms / growth & development
  • Haemophilus Infections / virology
  • Haemophilus influenzae / classification
  • Haemophilus influenzae / genetics
  • Haemophilus influenzae / growth & development*
  • Haemophilus influenzae / pathogenicity*
  • Humans
  • Inflammation
  • Mice
  • Mice, SCID
  • Respiratory System / cytology
  • Respiratory System / microbiology
  • Respiratory Tract Infections / microbiology
  • Respiratory Tract Infections / physiopathology
  • Virulence


  • Adhesins, Bacterial