Streptococcus pyogenes bacteria identified by the clear beta hemolysis it causes on blood agar of sheep. S. pyogenes are gram-positive bacteria that are rounded or spherical cocci. They typically form chains of cells. Healthy humans may carry these bacteria harmlessly in their throat or nose. Phatogenic strains of S. pyogenes, however, cause infections of the skin (including impetigo); the uterus following childbirth (puerperal sepsis) and the bloodstream (septicaaemia). S. pyogenes accounts for the high incidence of sore throats, tonsillitis, and middle ear infections (otitis media) in children. Treatment is with pennicilin drugs.