Streptococcus pyogenes (GAS) Streptococcus pyogenes infections

Streptococcus pyogenes appearance

  • Gram-positive cocci in chains (when cultivated in liquid media)
  • nonmotile
  • often encapsulated (capsule composed of hyaluronic acid)
  • non-spore-forming

Life-threatening infections caused by Streptococcus pyogenes

An estimated 700 million infections occur worldwide each year. While the overall mortality rate for these infections is 0.1%, over 650,000 of the cases are severe and invasive, and have a mortality rate of 25%. Early recognition and treatment are critical; diagnostic failure can result in sepsis and death (Wikipedia).

  • necrotizing fasciitis
  • toxic shock syndrome (TSS)
  • meningitis
  • bacterial pneumonia

Streptococcus pyogenes treatment
Selection of appropriate antibiotics depends on diagnosis!!

  • penicillin G


Other beta-lactam antibiotics, e.g.
  • amoxicillin
  • cefpodoxime
  • cefazolin
  • cefotaxime
(danger of macrolide resistance)
  • erythromycin
  • clarithromycin
  • azithromycin

  • clindamycin



Colony appearance

S.pyogenes Gram-stain Streptococcus pyogenes cell morphology Streptococcus group A appearance