Coloured scanning electron micrograph (SEM) of cultured oral bacteria forming a biofilm (plaque). Group of cocci (Streptococcus mutans) in glucan-like matrix. Streptococcus mutans is a coccoid shaped, Gram-positive, facultative anaerobic bacterium that is part of the normal bacteria flora of the mouth. It can thrive in temperatures ranging from 18-40 degrees Celsius. It metabolises sucrose to lactic acid and is a leading cause of tooth enamel decay. The acidic environment created in the mouth by this process is what causes the highly mineralized tooth enamel to decay. S. mutans is one of a few specialised organisms equipped with receptors for adhesion to the surface of teeth. Sucrose is utilized by S. mutans to produce a sticky, extracellular, dextran-based polysaccharide (glucan) that allows them to adhere to each other forming plaque. Other sugars (glucose, fructose, lactose) can be digested by S. mutans to produce lactic acid. It is the combination of plaque and acid that leads to tooth decay. Magnification: x4,000 when shortest axis printed at 25 millimetres.