2. M protein They are found in hair-like projections of the streptococcal surfaceand determine virulence Major virulent factor for group A streptococci. There are two major structural classes of M protein(class I &class II) and More than eighty serotypesof M protein of group A streptococci The class I M protein may be a virulence determinant for rheumatic fever Conserved antigenic domains on the class I M protein induce antibodies that cross react with cardiac muscle tissue T substance: Acid and heat labile unlike M protein, and has no relation to virulence of streptococci. 4. R protein Streptococcus pyogenes (Group A -hemolytic streptococci) The most pathogenic member of the genus It is present as a commensal in the nasopharynx in a variable proportion of healthy individuals. It produces different types of enzymes and exotoxins. 3.
Streptokinase: Fibrinolysin. It is an active proteolytic enzyme which lyses fibrin by catalytic conversion of plasminogen to plasmin. Has been given intravenously for the the treatment of pulmonary edema and of arterial and venous thrombosis
Streptodornase: Streptococcal deoxyribonuclease