The importance of the group a streptococcus capsule in the pathogenesis of human infections: a historical perspective

Clin Infect Dis. 2008 Apr 1;46(7):1038-45. doi: 10.1086/529194.


The virulence of group A streptococci (GAS) correlates closely with expression of its surface antigen, M protein, and its hyaluronic acid capsule. In studies of human GAS infection, the former has received considerable attention. For several decades, however, systematic identification of encapsulated virulent strains by the mucoid colonies they produce has been neglected in clinical studies. In part, this may be due to the capsule's evanescent expression on artificial media, its repression during convalescent carriage, lack of expertise in recognizing its colonial morphology, and the growing tendency for clinical laboratories to eschew throat cultures in favor of rapid laboratory tests for group A polysaccharide. Older and more recent studies are reviewed here that emphasize the capsule's basic role in infection. We believe that it is time to refocus newer clinical studies and techniques on achieving early recognition of potentially dangerous, heavily encapsulated strains of GAS for which spread may be prevented.

Publication types

  • Historical Article
  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Review

MeSH terms

  • Bacterial Capsules / physiology*
  • History, 20th Century
  • History, 21st Century
  • Humans
  • Streptococcal Infections / history
  • Streptococcal Infections / microbiology
  • Streptococcus pyogenes / pathogenicity*
  • Virulence
  • Virulence Factors / physiology*


  • Virulence Factors