Streptococcus bacteria. Transmission electron micrograph (TEM) of a section through a Streptococcus bacterium (upper centre) attached to a human tonsil cell (lower left). This beta- haemolytic (group A) Streptococcus bacterium is a spherical Gram-positive cocci. Surrounding the bacterial cell contents is the cell wall (thin, grey). Outside the cell wall is the capsule (dark, irregular) forming a loose slime layer. These bacteria are the most common cause of tonsillitis. To cause the disease they must attach firmly to the tonsil cell surface. When attached they can multiply and release harmful substances. Magnification x49,000 at 5x7cm size. x170,000 at 10x8"~PORTRAIT"