This antibody reacts with group A Streptococcus (GAS). It does not react with Streptococcus B, C, D, E, F or G, Corynebacterium diptheriae, Micrococcus mucilagines, Staphylococcus aureus, Streptococcus pneumoniae or Streptococcus salivarious. GAS are non-motile, non-spore forming bacteria that exist in pairs or as short chains. They are responsible for most cases of streptococcal illnesses including sore throat (strep thoat), scarlet fever and necrotizing fasciitis. The individual organisms are spheric in shape with a diameter of 0.6-1 mm. They produce 2 major classes of protein antigens: M antigens and T antigens of which the M protein is the major virulence factor.