Streptococcus bacteria. Colour transmission electron micrograph of a chain of Streptococcus pyogenes bacteria attached to human tonsils. Typically forming chains of cells, Streptococcus bacteria are rounded or spherical Gram-positive cocci. Surrounding the cells is the capsule forming a loose slime layer (blue). The two cells at bottom are dividing by binary fission to produce two new daughter cells. Healthy humans carry these bacteria harmlessly in their throat or nose. Pathogenic strains of S. pyogenes, however, cause sore throats, tonsillitis, scarlet fever and wound infections. Magnification x35,000 at 6x7cm size. Magnification: x120,000 at 10x8 inch print size.