Streptococcus pyogenes is a species of bacteria. Like most other streptococci, it is clinically important in human illness. It is an infrequent, but usually , part of the skin flora. It is the sole species of Lancefield group A and is often called group A streptococcus (GAS), because it displays streptococcal group A antigen on its cell wall. Group A streptococcal infection can cause illness, which typically produces small zones of beta-hemolysis, a complete of red blood cells. (A zone size of 2-3 mm is typical). It is thus also called group A (beta-hemolytic) streptococcus (GABHS).