Streptococcus mutans

Streptococcus mutans is a Gram-positive, facultatively anaerobic bacterium commonly found in the human oral cavity and is a significant contributor to tooth decay.The microbe was first described by Clarke in 1924.


Role in tooth decay

Early colonizers of the tooth surface are mainly Neisseria spp. and streptococci, including S. mutans. The growth and metabolism of these pioneer species changes local environmental conditions (e.g. Eh, pH, coaggregation, substrate availability), thereby enabling more fastidious organisms to further colonize after them, forming dental plaque.[4] Along with S. sobrinus, S. mutans plays a major role in tooth decay, metabolizing sucrose to lactic acid.[2] The acidic environment created in the mouth by this process is what causes the highly mineralized tooth enamel to be vulnerable to decay. S. mutans is one of a few specialized organisms equipped with receptors that help for better adhesion to the surface of teeth. Sucrose is utilized by S. mutans to produce a sticky, extracellular, dextran-based polysaccharide that allows them to cohere to each other forming plaque. S. mutans produces dextran via the enzyme dextransucrase (a hexosyltransferase) using sucrose as a substrate in the following reaction:

n sucrose → (glucose)n + n fructose

Sucrose is the only sugar that S. mutans can use to form this sticky polysaccharide.
Conversely, many other sugars—glucose, fructose, lactose—can be digested by S. mutans, but they produce lactic acid as an end product. It is the combination of plaque and acid that leads to dental decay.[5] Due to the role the S. mutans plays in tooth decay, there have been many attempts to make a vaccine for the organism. So far, such vaccines have not been successful in humans.[6] Recently, proteins involved in the colonization of teeth by S. mutans have been shown to produce antibodies that inhibit the cariogenic process.[7]