Streptococcus mutans- An Overview


Streptococcus mutans is a type of bacteria that is found in the human oral cavity and can cause tooth decay and cavities . It is a Gram-positive coccus that is arranged in chains or pairs and is part of the normal flora on mucosal membranes . It is classified into serotypes c, e, f, and k, with serotype c being the most common. It produces harmful acids from sugary foods that break down tooth enamel . It can be reduced by brushing, flossing, and limiting sugar intake.

Streptococcus mutans belongs to the lactic acid bacteria, which are a group of bacteria that produce lactic acid as a major end product of carbohydrate metabolism. Based on 16S rRNA gene sequence analysis, the genus Streptococcus belongs to the low G+C branch of the Gram-positive eubacteria, and is a member of the family Streptococcaceae. The genus currently consists of over 50 recognized species, which are grouped into different species groups based on various characteristics. S. mutans belongs to the mutans group, which is characterized by its heterogeneous genomic structure.

Streptococcus mutans was first discovered and named by J. Kilian Clarke in 1924, who isolated it from carious lesions and thought it was a mutant form of streptococci. However, it was not until the late 1950s and early 1960s that S. mutans gained widespread attention as an important etiologic agent of dental caries, based on clinical and animal studies. The natural habitat of S. mutans is the dental plaque, a multispecies biofilm that forms on the surfaces of teeth. S. mutans is a dominant species in dental biofilms due to its acid tolerance and ability to produce large quantities of extracellular polysaccharides (EPS) from sucrose, which aid in its colonization and biofilm formation.

Streptococcus mutans is not only a commensal bacterium but also an opportunistic pathogen that can cause infections when introduced into normally sterile sites or in immunocompromised patients . Besides dental caries, S. mutans has also been implicated in subacute bacterial endocarditis, a life-threatening inflammation of heart valves, as well as other extraoral pathologies such as cerebral microbleeds, IgA nephropathy, and atherosclerosis. The virulence factors of S. mutans include its biofilm formation, acid production and tolerance, carbohydrate metabolism, adhesion molecules, glucosyltransferases (GTFs), EPS synthesis, and bacteriocins (mutacins) .

Streptococcus mutans is a significant contributor to oral health and disease and has been extensively studied using biochemical, genetic, and molecular approaches. The complete genome sequence of S. mutans strain UA159 was published in 2001, which opened new avenues for understanding its biology and pathogenicity. S. mutans is one of the best characterized Gram-positive pathogens and serves as a model organism for studying oral microbiology and biofilm formation.