Streptococcus mutans is a Gram-positive cocci, Facultative anaerobic bacterium commonly found in the human oral cavity and is a significant contributor to tooth decay. J Kilian Clarke first described the microbe in 1924.
The first colonizers of the tooth surface are mainly Neisseria spp. and streptococci, including S. mutans. The pioneer species changes the local environmental conditions through growth and metabolism thus allowing more fastidious organisms to further colonize after them, forming dental plaque.
Since it metabolizes sucrose to lactic acid it can cause major tooth decay. Due to the acidic environment that this creates it makes the highly mineralized tooth enamel to be vulnerable to decay. It is one of the few organisms equipped with receptors that improve adhesion to the surface of teeth. It produces a sticky, extracellular, dextran-based polysaccharide that forms plaque. Sucrose is the only sugar it can use to form sticky polysaccharide. It can digest other sugars but they only produce lactic acid as an end product. The combination of plaque and acid leads to dental decay. There have been lots of attempts at a vaccine for the organism although unsuccessfully.