Streptococcus pyogenes, or Group A Streptococcus (GAS), produces a number of virulence factors. The M protein (d) is the organism's most important antiphagocytic factor, and it conveys serologic specificity-over 100 serotypes are now known. In the early stages of growth, the bacteria have hyaluronic acid (b) capsules. This capsule (similar to human hyaluronic acid structure) is rapidly destroyed by the organism's own hyaluronidase. Also known as spreading factor, hyaluronidase plays a role in GAS cellulitis. Erythrogenic toxin (a) is a superantigen produced by some strain of GAS lysogenized by a bacteriophage carrying the toxin gene; it causes the rash of scarlet fever. A second superantigen, streptococcal pyrogenic toxin, causes streptococcal toxic shock syndrome. Streptolysin O (e) an oxygen-labile hemolysin is useful for identification of the organism and is antigenic so antistreptolysin antibodies can be used to diagnosis rheumatic fever, a sequelae of GAS infection. Lipoteichoic acid (c) is a component of the cell wall that is involved in binding of the bacterium to host fibronectin.