streptococcus

Streptococcus pyogenes:
Important properties:
• Gram-positive cocci in chains.
• Usually, it is uncapsulated( but most pathogenic strains have capsule).
• Catalase negative.
• Non motile.
• ?-hemolytic.



Antigenic structures and virulence factors :
Structural components:
• Antigen-C: of cell wall is used to classify the genus serologically into 20 serogroups (Lancefield system). St.pyogenes belongs to group-A streptococci(GAS).
• M-protein is surface protein mediate adherence and prevent phagocytosis. St.pyogenes has more than 150 serotypes basis on M-protein (Griffith typing).
Enzymes :
• Streptokinase(fibrinolysin) transforms the plasminogen into plasmin, which active proteolytic enzyme that digests fibrin clot, therefore break down fibrin barrier around lesion and spreading infection. Now Streptokinase has been given intravenously for treatment of pulmonary emboli, coronary artery and venous thrombosis.
• Hayluronidase; assist streptococcal growth in the tissue by liquefying inflammatory exudates. It break down hyaluronic acid of host connective tissue , and spreading infection.