Streptococcus (Str.) /strep′təkok″əs/ [Gk, streptos + kokkos, berry] , adj., a genus of nonmotile gram-positive cocci classified by serological types (Lancefield groups A through T), by hemolytic action (α, β, γ) when grown on blood agar, and by reaction to bacterial viruses (phage types 1 to 86). The various species occur in pairs, short chains, and chains. Some are facultative aerobes, and some are anaerobic. Some species also are hemolytic, and others are nonhemolytic. Many species cause disease in humans. Streptococcus faecalis, a penicillin-resistant group D enterococcus and normal inhabitant of the GI tract, may cause infection of the urinary tract or endocardium. S. pneumoniae (formerly Diplococcus pneumoniae) causes a majority of the cases of bacterial pneumonia in the United States. S. pyogenes belongs to group A and may cause tonsillitis and respiratory, urinary, or skin infections. Some beta-hemolytic strains may lead to rheumatic fever or to glomerulonephritis. S. viridans, a member of the normal flora of the mouth, is the most common cause of bacterial endocarditis, especially when introduced into the bloodstream during dental procedures. −streptococcal, adj.
