Genetics of group A streptococci

Streptococcus pyogenes (the group A streptococcus) is remarkable in terms of the large number of very different diseases it can cause in humans. These range from superficial and self-limiting diseases of the pharynx (e.g., pharyngitis, commonly known as strep throat) and skin (impetigo) to infections that involve increasingly deeper layers of tissue and are associated with increasing degrees of destruction of tissue (e.g., erysipelas, cellulitis, necrotizing fasciitis, and myositis). The organism has the ability to spread rapidly through tissue and to penetrate into the vasculature to cause lethal sepsis. Other diseases result from the production of toxins that spread through tissue or spread systemically from a site of local infection (scarlet fever and toxic shock syndrome). Still other diseases are the result of an immunopathological response on the part of the host that is triggered by a streptococcal infection. These diseases include rheumatic fever, acute glomerulonephritis, certain types of psoriasis, and potentially even some forms of obsessive-compulsive syndrome disorder (pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections).