beta-hemolytic streptococci, the pyogenic streptococci of groups A, B, C, E, F, G, H, K, L, M, and O that cause hemolysis of red blood cells in blood agar in the laboratory. These organisms cause most of the acute streptococcal infections seen in humans, including scarlet fever, many cases of pneumonia and sepsis syndrome, and streptococcal sore throat. Penicillin is usually prescribed to treat these infections when they are suspected, even before the results of the bacteriological culture are available, because it is known that these organisms as a group are usually sensitive to the effects of penicillin and because the sequelae of untreated streptococcal infection may include glomerulonephritis and rheumatic fever.
