Streptococcus mutans characteristics, diseases

Egbert Haynes
Streptococcus mutans characteristics, diseases

Streptococcus mutans It is a bacterium that participates in the formation of dental plaque or biofilm that forms on the enamel of the teeth. It is a microorganism that belongs to the oral microbiota in humans and represents 39% of the total Streptococcus in that area.

It has been identified as the main causal agent for the onset of dental caries, a disease characterized by the destruction of the hard tissues of the tooth. In fact, he was first isolated by J. Kilian Clarke from a carious lesion..

By KDS4444 [CC BY-SA 4.0 (], from Wikimedia Commons

The predisposition of some people to suffer more caries episodes than others has to do with multiple factors, including poor oral hygiene, the presence of cariogenic microorganisms and the abuse of foods rich in sucrose. These factors influence the imbalance of the oral microbiota, where the population of S. mutans.

The prevalence of dental caries in the population is quite frequent. It is estimated that 88.7% of people between 5 and 65 years of age have presented at least one episode of dental caries in their lives, with children and adolescents being the most vulnerable population.

Article index

  • 1 Features
  • 2 Taxonomy
  • 3 Morphology
  • 4 Virulence factors
  • 5 Pathogenesis
    • 5.1 Production of glucosyltransferases
    • 5.2 Adhesion capacity and biofilm formation
    • 5.3 Acid production and ability to survive low pH
  • 6 Diseases or pathologies
    • 6.1 Tooth decay
    • 6.2 Periodontitis
    • 6.3 Loss of teeth
    • 6.4 Bacterial endocarditis
  • 7 Transmission
  • 8 Diagnosis
  • 9 Prevention
  • 10 Treatment
  • 11 References


Streptococcus mutans. Gram stain. By Photo Credit: Content Providers (s): Streptococcus mutansTranswiki approved by: w: en: User: Dmcdevit [Public domain], via Wikimedia Commons

-They are characterized by being facultative anaerobes, which means that they can live in the presence or absence of oxygen.

-They require 5 -10% CO2 to grow in the laboratory, which is why they are called microerophiles.

-According to the hemolysis produced in the culture medium, blood agar is classified as alpha or gamma hemolytic.

-They are microorganisms very susceptible to environmental changes, so they do not survive long outside the body.

-At the laboratory level they are very demanding from a nutritional point of view.


Streptococcus mutans belongs to the Domain Bacteria, Phylum Firmicutes, Class Bacilli, Order Lactobacillales, Family Streptococaceae, Genus Streptococcus, Specie mutans.

The absence of carbohydrate C in its cell wall means that it cannot be classified in the Lancefield groups. That is why it was included within the group called Streptococcus viridans.

However, there is another classification based on the sequence analysis of the 16SrRNA gene. In this sense, it was classified as a Group of “S. mutans", Which does not include a single species, but houses other antigenically similar Streptococci such as: S. mutans, S. sobrinus, S. cricetus, S. macacae, S. rattus, S. downeii, and S. ferus.

Many of these species are typical of some animals and are rarely found in man. Alone S. mutans Y S. sobrinus They are the usual microbiota of the human oral cavity.


Streptococcus mutans they are spherical cells, which is why they are called cocci. They are arranged in chains.

They do not form spores and are not motile. When they are stained with the Gram staining technique, they turn purple, that is, they are Gram positive..

They do not have a capsule, but have a typical Gram positive bacterial wall.

It contains a thick 80 nm thick peptidoglycan, in which teichoic acid is anchored, while lipoteichoic acid is attached to the cell membrane..

They do not have carbohydrate C in their cell wall.

Virulence factors

Virulence factors are those mechanisms that the microorganism has to cause disease. S. mutans has:

  • Production of glucosyltransferases.
  • Adhesion capacity and biofilm formation.
  • Production of high quantity of organic acids (acidogenicity).
  • Ability to survive low pH (acidicity).


Production of glucosyltransferases

Glycosyltransferases B, C and D are enzymes that have the responsibility of degrading the carbohydrate sucrose into dextrans and levhans, which are the most important polyglycans..

These act on the aggregation of microorganisms on the dental surface, creating microcolonies that favor the formation of biofilm.

Adhesion capacity and biofilm formation

S. mutans has the ability to adhere to the dental film, which is a very thin physiological mineralized organic layer on the surface of the teeth, composed of proteins and glycoproteins.

Once attached to the dental film, these bacteria have the property of adhering to other bacteria, through the formation of extracellular glucan polymers, acting as a glue that holds all the plaque together and strong. This is how the biofilm or pathological dental plaque is formed.

Acid production and ability to survive low pH

S. mutans, Once installed in the dental plaque, it metabolizes the monosaccharides and disaccharides present in the daily diet, such as glucose, fructose, sucrose, lactose and maltose, carrying out bacterial glycolysis, which results in the production of acids, including lactic acid. , propionic, acetic and formic.

But besides that,  S. mutans can synthesize intracellular polysaccharides that are metabolized to produce acids in the absence of exogenous fermentable carbohydrates.

This means that, S. mutans can lower the pH to 4.2 inside dental plaque, even between meals, being able to survive this pH continuously.

All these acids react with the hydroxyapatite of the enamel, causing the demineralization of the tooth. This represents the main cariogenic mechanism of this bacterium..

Diseases or pathologies

Dental caries

It is considered that S. mutans it is the microorganism that initiates the caries process, mainly in the superficial chewing fissures or between the teeth.

However, other microorganisms such as S. salivarius, S. sanguis, S sobrinus, Lactobacilli acidophilus, L. casei, Actinomycetus viscosus, Actinomycetos naeslundii and Bifidobacterium spp.

Caries are characterized by the appearance of a black spot on the tooth surface that can progress from the enamel to the pulp and can spread to the periodontium. This process is favored by high sugar concentrations and low pH..


It begins with gingivitis (inflammation of the gums), later it progresses to periodontitis (inflammation of the periodontium), where there is a loss of dental support due to resorption of the alveolar bone and periodontal ligaments.

Loss of teeth

It is the consequence of poor oral care and hygiene, where tooth decay and periodontitis cause the total loss of the tooth..

Bacterial endocarditis

It has been observed that some patients who have developed bacterial endocarditis have Streptococcus of the Viridans Group as the causative agent, among which is S. mutans.

This has coincided with poor oral hygiene and periodontal disease in these patients, which suggests that the entrance door is the oral lesion..


It is believed that the S. mutans it is acquired as a habitual oral microbiota at an early age, through contact with the mother (vertical transmission), and can be transmitted through saliva from one individual to another (horizontal transmission).


Streptococcus mutans it is catalase and oxidase negative like all Streptococcus. They are isolated in enriched culture media such as blood agar.

They grow at 37 ºC with 10% COtwo in 24 hours of incubation in microaerophilic hoods. Colonies are small and alpha or gamma hemolytic.

S. mutans It hydrolyzes esculin and produces acid from mannitol and sorbitol. They are identified with the API Rapid STREP system.


The prevention and control of dental plaque is vital to avoid the appearance of cavities, periodontitis and the loss of teeth.

Saliva is a natural mechanism that protects against tooth decay, thanks to the content of lysozymes, sialoperoxidase and immunoglobulin IgA.

Other natural defenses are the presence of some bacteria such as Streptococcus gordonii,  Streptococcus sanguinis and  Veillonella parvula, that antagonize the growth of S. mutans by the production of HtwoORtwo.

However, this is not enough, it is necessary to take other preventive measures..

To do this, you must maintain good oral hygiene. This consists of daily brushing with fluoride-containing toothpaste after each meal, flossing and using mouthwashes..

In addition to this, it will be necessary to visit the dentist regularly to perform periodic review and cleaning of dental plaque, in addition to avoiding excess sweets, especially in children..


Treatment is often expensive. The teeth can be saved as long as it is attacked at the beginning.

Sometimes root canal treatment may be needed when decay reaches the dental pulp. In the worst case, the extraction of the complete piece and placement of the prosthesis will be carried out..


  1. Lemos JA, Quivey RG, Koo H, Abranches J. Streptococcus mutans: a new Gram-positive paradigm? Microbiology. 2013; 159 (3): 436-445.
  2. Krzyściak W, Jurczak A, Kościelniak D, Bystrowska B, Skalniak A. The virulence of Streptococcus mutans and the ability to form biofilms. European Journal of Clinical Microbiology & Infectious Diseases. 2014; 33 (4): 499-515.
  3. Ryan KJ, Ray C. SherrisMicrobiology Medical, 6th Edition McGraw-Hill, New York, U.S.A; 2010. p 688-693
  4. Ojeda-Garcés Juan Carlos, Oviedo-García Eliana, Luis Andrés Rooms. Streptococcus mutans and tooth decay. CES odontol.  2013; 26 (1): 44-56.
  5. Wikipedia contributors. Streptococcus mutans. Wikipedia, The Free Encyclopedia. March 23, 2018, 12:08 UTC. Available at: Accessed September 3, 2018.
  6. Roa N, Gómez S, Rodríguez A. Response of T cells, cytokines and antibodies against the peptide (365-377) of the cell adhesion protein of Streptococcus mutans. Univ Odontol. 2014; 33 (71): 29-40.
  7. Graciano M, Correa Y, Martínez C, Burgos A, Ceballos J, Sánchez L. Streptococcus mutans and dental caries in Latin America. Systematic review of the literature. Rev Nac de Odontol. 2012; 8 (14): 32-45.
  8. Berkowitz RJ. Acquisition and transmission of mutans streptococci. J Calif Dent Assoc. 2003; 31 (2): 135-8.

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