virulence and pathogenicity
Last reviewed 12/2022
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