Bacteria on an epithelial cell from the human tongue filiform papilla, coloured scanning electron micrograph (SEM). Coccoid bacteria (likely Streptococcus mutans due to the fibrous glucan matrix that surrounds the cells) and one rod bacterium are seen on the epithelial surface. Most bacteria on the human tongue are harmless or even beneficial. However some bacteria can cause throat infections and form plaque deposits on teeth. Plaque will also lead to tooth decay and periodontal disease. Magnification: x5, 000 when shortest axis printed at 25 millimetres.