Streptococcus pyogenes. Coloured transmission electron micrograph (TEM) of the bacteria Streptococcus pyogenes, forming an S-shaped chain. S.pyogenes is a spherical, Gram-positive bacteria that typically forms chains. Healthy humans may carry this bacterium in their throat or nose. Pathogenic strains of S.pyogenes cause infections of the skin (including impetigo); uterus following childbirth (puerperal sepsis); bloodstream (septi- caemia); and scarlet fever. S.pyogenes accounts for much of the high incidence of sore throats and tonsillitis in young children. The use of penicillin drugs are effective as a treatment. Magnification: x7,000 at 6x4.5cm size.