Streptococcus pyogenes is a species of Gram-positive, aerotolerant bacterium in the genus "Streptococcus". These bacteria are extracellular, and made up of non-motile and non-sporing cocci. It is clinically important for humans. It is an infrequent, but usually pathogenic, part of the skin microbiota. It is the predominant species harboring the Lancefield group A antigen, and is often called group A "Streptococcus" (GAS). However, both "Streptococcus dysgalactiae" and the "Streptococcus anginosus" group can possess group A antigen. Group A streptococci when grown on blood agar typically produces small zones of beta-hemolysis, a complete destruction of red blood cells. (A zone size of 2–3 mm is typical.) It is thus also called group A (beta-hemolytic) "Streptococcus" (GABHS), and it can make colonies greater than 5 mm in size.