[strepto- + coccus]
ABBR: Str A genus of gram-positive, facultatively anaerobic cocci of the family Streptococcaceae, in which the cells tend to form chains or pairs. Many species are saprophytes, but others are virulent pathogens. They may be classified as alpha (α), beta (β), and gamma (γ) on the basis of their growth on blood agar plates and the hemolysis produced. Alpha-hemolytic streptococci produce partial hemolysis and create a greenish coloration around the colonies. Beta-hemolytic types completely hemolyze blood and form clear zones round colonies; those of the gamma type are nonhemolytic and do not change the color of the medium. Streptococci are also classified into several immunological groups (Lancefield groups) designated by the letters A through H, and K through O. Most human infections are caused by groups A, B, D, F, G, H, K, and O. Approximately 100 types of group A beta-hemolytic streptococci have been identified.
SEE: rheumatic fever; SEE: scarlet fever
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