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Haemolytic streptococci --> beta-haemolytic streptococci

Those that produce active haemolysins (O and S) which cause a zone of clear haemolysis on the blood agar medium in the area of the colony; beta-haemolytic streptococci are divided into groups (a to O) on the basis of cell wall c carbohydrate (see Lancefield classification); group A (in the strains pathogenic for man) comprises more than 50 types (designated by arabic numerals) determined by cell wall m protein, which seems to be associated closely with virulence and is produced chiefly by strains with matt or mucoid colonies, in contrast to nonvirulent, glossy colony-producing strains; other surface protein antigens such as R and t (t substance), and the nucleoprotein fraction (P substance) seem to be of less importance. The more than 20 extracellular substances elaborated by strains of beta-haemolytic streptococci include erythrogenic toxin (elaborated only by lysogenic strains), deoxyribonuclease (streptodornase), haemolysins (streptolysins O and S), hyaluronidase, and streptokinase.

Synonym: haemolytic streptococci.