Streptococcus bacteria. Illustration of a chain of Streptococcus bacteria. These rounded or spherical Gram-positive bacteria have a cell wall (thin, white) surrounding the cell contents (pink). In the centre of the cell contents is the nuclear material (purple). Because the bacteria always divide in the same plane they tend to form chains of cells, as seen here. Surrounding the cells is the capsule forming a loose slime layer. This gel-like layer is associated with pathogenic strains of the bacteria and is thought to protect the cell against the immune system. Pathogenic Streptococcus can cause sore throats, tonsillitis, scarlet fever and wound infections.