Streptococcus bacteria. Coloured transmission electron micrograph (TEM) of chains of bacteria, Streptococcus pyogenes. Typically forming chains of cells, these Gram-positive bacteria are rounded or spherical cocci. Healthy humans may carry these bacteria harmlessly in their throat or nose. Pathogenic strains of S. pyogenes, however, account for the high incidence of sore throats, tonsilli- tis, and middle ear infections (otitis media) in children. The bacteria may also cause skin infect- ions (including impetigo); puerperal sepsis of the uterus following childbirth; and blood poisoning (septicaemia). Treatment is with penicillin drugs. Magnification: x8000 at 6x4.5cm size.