Streptococcus bacterium. Coloured transmission electron micrograph of a section through a Streptococcus bacterium attached to a human tonsil cell (at lower frame). This beta- haemolytic (group A) Streptococcus bacterium (top) is a rounded or spherical Gram-positive cocci. Surrounding the bacterial cell contents (green) is the cell wall (thin, red). Around the outside is the capsule (green-brown, irregular) forming a loose slime layer. These bacteria are the most common cause of tonsillitis. They attach to the surface of the tonsil, multiply and release harmful substances. Magnification: x26, 600 at 5x7cm size. x90,000 at 10x8"~PORTRAIT"