A genus of spherical Gram-positive bacteria that usually occur in pairs or chains; most strains are nonmotile.

Most species are parasites or pathogens of animals, often occurring in the respiratory or alimentary tracts.

Some species are hemolytic; that is, they destroy red blood cells, and cause such diseases as scarlet fever and rheumatic fever.

Streptococci are killed by pasteurization and common disinfectants; penicillin, tetracycline, and other antibiotics are effective against hemolytic strains.