Group A beta-hemolytic streptococci

(GABHS) are gram-positive bacteria that grow in culture as pairs or chains of variable length. On sheep blood agar they appear as transpar-ent to opaque, round, small colonies surrounded by a zone of complete hemolysis (beta) of red cells. The beta-hemolytic streptococci include the pathogens of Lancefield groups A, C, and G. In contrast, viridans streptococci produce partial (alpha) or no (gamma) hemolysis. Group D streptococci produce variable hemol-ysis, and S pneumoniae (pneumo-coccus) produce alpha-hemolysis. Biologic products elaborated by GABHS are important determinants of virulence. Antibody responses to these antigens sometimes are used to identify these bacteria as the cause of an infection. In addition to hemo-lysins (including streptolysins O and S), GABHS may elaborate strepto-kinase, streptodornase, bacteriocins, deoxyribonuclease, exotoxins, hyalu-ronidase, nicotinamide adenine dinu-cleotidase, and proteinase