Group A Streptococci:

Streptococcus pyogenes ("pus producing") are pathogenic bacteria of man. Group A streptococci express a variety of both cell surface and extracellular virulence factors that are responsible for a variety of human diseases. The group is defined by the presence of a polysaccharide composed of N-acetylglucosamine and rhamnose associated with the cell wall; see Dr. Lancefield's bibliography for further reading on the topic.