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Virulence and pathogenicity

Authoring team

The following extracellular toxins have been characterised:

  • streptokinase - lyses fibrin by catalysing conversion of plasminogen to plasmin. Also produced by some members of Lancefield Groups B,C,G and F.
  • hyaluronidase - may contribute to invasiveness
  • hyaluronic capsule - protects organism from host defences
  • NADase - nicotinamide adenine dinucleotidase - kills leucocytes
  • haemolysins - two key types, both toxic to leucocytes:
    • streptolysin S - responsible for beta haemolysis
    • streptolysin O - used in serodiagnosis
    • also, deoxyribonuclease
  • erythrogenic toxin - produced by strains infected with lysogenic phage; responsible for rash of scarlet fever. Non-immunity demonstrated by Dick test - injection intradermally produces localised erythema.
  • surface protein antigens - M antigen associated with virulence (epithelial adhesion and anti-phagocytic / complement activity; T and R not virulent - used in epidemiologic studies
  • other enzymes - include leucocidin, protease and amylase

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