The group A streptococcus bacterium (Streptococcus pyogenes, or GAS) is a form of β-hemolytic Streptococcus bacteria responsible for most cases of streptococcal illness. Other types (B, C, D, and G) may also cause infection. Several virulence factors contribute to the pathogenesis of GAS, such as M protein, hemolysins, and extracellular enzymes.
Streak plate of Streptococcus pyogenes (incubated @ 37 degrees C for 48 hrs) showing beta hemolysis, complete lysis of red blood cells, around the isolated colonies. Image taken using transmitted light.