ABSTRACT
Alpha-hemolytic streptococcal colonies are surrounded by a narrow zone of hemolysis that shows green discoloration based on the hemolysin's action on the hemoglobin; beta-hemolytic streptococci show a well-defined clear zone of hemolysis around the colony; gamma-hemolytic streptococci have no effect on the red blood cells. Nearly all strains of Streptococcus pneumoniae are alpha-hemolytic but have been shown to exhibit beta-hemolysis during anaerobic incubation. Most clinical isolates appear as beta-hemolytic streptococci when grown on blood agar. All these proteins have been implicated in some way with streptococcal pathogenesis; however, the people discusses the major virulence determinant, the M protein, in detail. The members of the viridans group are historically considered difficult to differentiate on the species level, as they do not contain C-carbohydrate antigens in their cell walls, they cannot be serologically identified using the traditional methods described for the beta-hemolytic streptococci.
