''Streptococcus mutans'' is a
facultatively anaerobic
A facultative anaerobic organism is an organism that makes ATP by aerobic respiration if oxygen is present, but is capable of switching to fermentation if oxygen is absent.
Some examples of facultatively anaerobic bacteria are ''Staphylococcus' ...
,
gram-positive
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Gram-positive bacte ...
coccus
A coccus (plural cocci) is any bacterium or archaeon that has a spherical, ovoid, or generally round shape. Bacteria are categorized based on their shapes into three classes: cocci (spherical-shaped), bacillus (rod-shaped) and spiral ( of whi ...
(round
bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
) commonly found in the
human
Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...
oral cavity
In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...
and is a significant contributor to
tooth decay
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
.
It is part of the "
streptococci" (plural, non-italic lowercase), an informal general name for all species in the genus ''Streptococcus''. The microbe was first described by
James Kilian Clarke in 1924.
This bacterium, along with the closely related species ''
Streptococcus sobrinus
''Streptococcus sobrinus'' is a Gram-positive, catalase-negative, non-motile, and Anaerobic organism, anaerobic member of the genus ''Streptococcus''.
Pathology
''Streptococcus sobrinus'' in conjunction with the closely related species ''Strept ...
'', can cohabit the mouth: Both contribute to oral disease, and the expense of differentiating them in laboratory testing is often not clinically necessary. Therefore, for clinical purposes they are often considered together as a group, called the mutans streptococci (plural, non-italic due to its being an informal group name). This grouping of similar bacteria with similar
tropism
A tropism is a biological phenomenon, indicating growth or turning movement of a biological organism, usually a plant, in response to an environmental stimulus. In tropisms, this response is dependent on the direction of the stimulus (as oppose ...
can also be seen in the
viridans streptococci
The viridans streptococci are a large group of commensal streptococcal Gram-positive bacteria species that are α-hemolytic, producing a green coloration on blood agar plates (hence the name "viridans", from Latin "vĭrĭdis", green), although ...
, another group of ''Streptococcus'' species.
Ecology
''S. mutans'' is naturally present in the human oral microbiota, along with at least 25 other species of oral streptococci. The
taxonomy
Taxonomy is the practice and science of categorization or classification.
A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
of these bacteria remains tentative. Different areas of the oral cavity present different ecological niches, and each species has specific properties for colonizing different oral sites. ''S. mutans'' is most prevalent on the pits and
fissures
A fissure is a long, narrow crack opening along the surface of Earth. The term is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in Earth's crust, on ice sheets and glaciers, and on volcanoes.
Ground fissure
...
, constituting 39% of the total streptococci in the oral cavity. Fewer ''S. mutans'' bacteria are found on the buccal surface (2–9%).
Bacterial-fungal co-coaggregation can help to increase the cariogenic potential of ''S. mutans''. A symbiotic relationship with ''S. mutans'' and ''
Candida albicans
''Candida albicans'' is an opportunistic pathogenic yeast that is a common member of the human gut flora. It can also survive outside the human body. It is detected in the gastrointestinal tract and mouth in 40–60% of healthy adults. It is us ...
'' leads to increased glucan production and increased biofilm formation. This therefore amplifies the cariogenic effect of ''S. mutans''.
Oral streptococci have both harmless and harmful bacteria. However, under special conditions commensal streptococci can become opportunistic pathogens, initiating disease and damaging the host. Imbalances in the microbial biota can initiate oral diseases.
''C. albicans'' is an opportunistic pathogenic yeast that can be found within the oral cavity.
Its presence in the biofilm promotes higher levels of ''S. mutans'' when looking at
early childhood caries Early childhood caries (ECC), formerly known as nursing bottle caries, baby bottle tooth decay, night bottle mouth and night bottle caries, is a disease that affects teeth in children aged between birth and 71 months.American Academy of Pediatric De ...
.
It stimulates the formation of ''S. mutans'' microcolonies.
This is achieved through low concentrations of cross-kingdom metabolites, such as
farnesol
Farnesol is a natural 15-carbon organic compound which is an acyclic sesquiterpene alcohol. Under standard conditions, it is a colorless liquid. It is hydrophobic, and thus insoluble in water, but miscible with oils.
Farnesol is produced from 5- ...
, derived from the
biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
.
It has been suggested that when both microbes are present, more biofilm matrix is produced, with a greater density.
When
farnesol
Farnesol is a natural 15-carbon organic compound which is an acyclic sesquiterpene alcohol. Under standard conditions, it is a colorless liquid. It is hydrophobic, and thus insoluble in water, but miscible with oils.
Farnesol is produced from 5- ...
is in high concentration, it inhibits the growth of both ''S. mutans'' and ''C. albicans''.
This decreases the biofilm pathogenesis, and therefore its
caries
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
promoting potential.
This offers the potential for an anti-fungal to be used in the prevention of
dental caries
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
.
Role in disease
Tooth decay
Early colonizers of the tooth surface are mainly ''
Neisseria
''Neisseria'' is a large genus of bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens, '' N. meningitidis'' and ''N. gonorrhoeae''.
''Neisseria'' species are Gram-negativ ...
'' spp. and
streptococci, including ''S. mutans''. They must withstand the oral cleansing forces (e.g. saliva and the tongue movements) and adhere sufficiently to the dental hard tissues. The growth and metabolism of these pioneer species changes local environmental conditions (e.g., Eh, pH, coaggregation, and substrate availability), thereby enabling more fastidious organisms to further colonize after them, forming
dental plaque
Dental plaque is a biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found bet ...
. Along with ''
S. sobrinus'', ''S. mutans'' plays a major role in tooth decay,
metabolizing
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
to
lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
.
[ The ]acidic
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a sequ ...
environment created in the mouth by this process is what causes the highly mineralized tooth enamel
Tooth enamel is one of the four major Tissue (biology), tissues that make up the tooth in humans and many other animals, including some species of fish. It makes up the normally visible part of the tooth, covering the Crown (tooth), crown. The ...
to be vulnerable to decay. ''S. mutans'' is one of a few specialized organisms equipped with receptors that improve adhesion to the surface of teeth. ''S. mutans'' uses the enzyme glucansucrase
Glucansucrase (also known as glucosyltransferase) is an enzyme in the glycoside hydrolase family GH70 used by lactic acid bacteria to split sucrose and use resulting glucose molecules to build long, sticky biofilm chains. These extracellular ho ...
to convert sucrose into a sticky, extracellular, dextran
Dextran is a complex branched glucan (polysaccharide derived from the condensation of glucose), originally derived from wine. IUPAC defines dextrans as "Branched poly-α-d-glucosides of microbial origin having glycosidic bonds predominantly C-1 ...
-based polysaccharide
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
that allows them to cohere, forming plaque. ''S. mutans'' produces dextran via the enzyme dextransucrase (a hexosyltransferase Hexosyltransferases are a type of glycosyltransferase that catalyze the transfer of a hexose.
Examples include:
* glucosyltransferases - transfer glucose
* galactosyltransferases - transfer galactose
* fucosyltransferases - transfer fucose
* ...
) using sucrose as a substrate in the following reaction:
: ''n'' sucrose → (glucose)''n'' + ''n'' fructose
Sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
is the only sugar that bacteria can use to form this sticky polysaccharide.[
However, other sugars—]glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
, fructose
Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...
, lactose
Lactose is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C12H22O11. Lactose makes up around 2–8% of milk (by mass). The name comes from ' (gen. '), the Latin word for milk, plus the suffix '' - ...
—can also be digested by ''S. mutans'', but they produce lactic acid
Lactic acid is an organic acid. It has a molecular formula . It is white in the solid state and it is miscible with water. When in the dissolved state, it forms a colorless solution. Production includes both artificial synthesis as well as natu ...
as an end product. The combination of plaque and acid leads to dental decay. Due to the role ''S. mutans'' plays in tooth decay, many attempts have been made to create a vaccine
A vaccine is a biological Dosage form, preparation that provides active acquired immunity to a particular infectious disease, infectious or cancer, malignant disease. The safety and effectiveness of vaccines has been widely studied and verifie ...
for the organism. So far, such vaccines have not been successful in humans. Recently, proteins involved in the colonization of teeth by ''S. mutans'' have been shown to produce antibodies that inhibit the cariogenic process.
A molecule recently synthesized at Yale University and the University of Chile, called Keep 32, is supposed to be able to kill ''S. mutans''. Another candidate is a peptide called C16G2, synthesised at UCLA.
It is believed that ''Streptococcus mutans'' acquired the gene that enables it to produce biofilms through horizontal gene transfer with other lactic acid bacterial species, such as ''Lactobacillus''.
Life in the oral cavity
Surviving in the oral cavity, ''S. mutans'' is the primary causal agent and the pathogenic species responsible for dental caries (tooth decay or cavities) specifically in the initiation and development stages.
Dental plaque
Dental plaque is a biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found bet ...
, typically the precursor to tooth decay, contains more than 600 different microorganisms, contributing to the oral cavity's overall dynamic environment that frequently undergoes rapid changes in pH, nutrient availability, and oxygen tension. Dental plaque adheres to the teeth and consists of bacterial cells, while plaque is the biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
on the surfaces of the teeth. Dental plaque and ''S. mutans'' is frequently exposed to "toxic compounds" from oral healthcare products, food additives, and tobacco.
While ''S. mutans'' grows in the biofilm, cells maintain a balance of metabolism that involves production and detoxification. Biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
is an aggregate of microorganisms in which cells adhere to each other or a surface. Bacteria in the biofilm community can actually generate various toxic compounds that interfere with the growth of other competing bacteria.
''S. mutans'' has over time developed strategies to successfully colonize and maintain a dominant presence in the oral cavity. The oral biofilm is continuously challenged by changes in the environmental conditions. In response to such changes, the bacterial community evolved with individual members and their specific functions to survive in the oral cavity. ''S. mutans'' has been able to evolve from nutrition-limiting conditions to protect itself in extreme conditions. Streptococci represent 20% of the oral bacteria and actually determine the development of the biofilms. Although ''S. mutans'' can be antagonized by pioneer colonizers, once they become dominant in oral biofilms, dental caries can develop and thrive.
Cariogenic potential
The causative agent of dental caries is associated with its ability to metabolize various sugars, form a robust biofilm, produce an abundant amount of lactic acid, and thrive in the acid environment it generates. A study into pH of plaque said that the critical pH for increased demineralisation of dental hard tissues (enamel and dentine) is 5.5. The Stephan curve illustrates how quickly the plaque pH can fall below 5.5 after a snack or meal.
Dental caries
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
is a dental biofilm-related oral disease associated with increased consumption of dietary sugar and fermentable carbohydrates. When dental biofilms remain on tooth surfaces, along with frequent exposure to sugars, acidogenic bacteria (members of dental biofilms) will metabolize the sugars to organic acids. Untreated dental caries is the most common disease affecting humans worldwide . Persistence of this acidic condition encourages the proliferation of acidogenic and aciduric bacteria as a result of their ability to survive at a low-pH environment. The low-pH environment in the biofilm matrix erodes the surface of the teeth and begins the "initiation" of the dental caries. ''Streptococcus mutans'' is a bacterium which is prevalent within the oral environment and is thought to be a vital microorganism that contributes to this initiation. ''S. mutans'' thrives in acidic conditions, becoming the main bacterium in cultures with permanently reduced pH . If the adherence of ''S. mutans'' to the surface of teeth or the physiological ability (acidogenity and aciduricity) of ''S. mutans'' in dental biofilms can be reduced or eliminated, the acidification potential of dental biofilms and later cavity formations can be decreased.
Ideally, we can stop the early various lesion developing beyond the white spot stage. Once beyond here, the enamel surface is irreversibly damaged and cannot be biologically repaired. In young children, the pain from a carious lesion can be quite distressing and restorative treatment can cause an early dental anxiety to develop. Dental anxiety has knock-on effects for both dental professionals and patients. Treatment planning and therefore treatment success can be compromised. The dental staff can become stressed and frustrated when working with anxious children. This can compromise their relationship with the child and their parents. Studies have shown a cycle to exist, whereby dentally anxious patients avoid caring for the health of their oral tissues. They can sometimes avoid oral hygiene and will try to avoid seeking dental care until the pain is unbearable.
Susceptibility to disease varies between individuals and immunological mechanisms have been proposed to confer protection or susceptibility to the disease. These mechanisms have yet to be fully elucidated but it seems that while antigen presenting cells are activated by ''S. mutans'' ''in vitro'', they fail to respond ''in vivo''. Immunological tolerance to ''S. mutans'' at the mucosal surface may make individuals more prone to colonisation with ''S. mutans'' and therefore increase susceptibility to dental caries.
In children
''S. mutans'' is often acquired in the oral cavity subsequent to tooth eruption, but has also been detected in the oral cavity of predentate children. It is generally, but not exclusively, transmitted via vertical transmission from caregiver (generally the mother) to child. This can also commonly happen when the parent puts their lips to the child's bottle to taste it, or to clean the child's pacifier, then puts it into the child's mouth.
Cardiovascular disease
''S. mutans'' is implicated in the pathogenesis of certain cardiovascular diseases, and is the most prevalent bacterial species detected in extirpated heart valve tissues, as well as in atheromatous plaques, with an incidence of 68.6% and 74.1%, respectively. ''Streptococcus sanguinis'', closely related to ''S. mutans'' and also found in the oral cavity, has been shown to cause Infective Endocarditis.
''Streptococcus mutans'' has been associated with bacteraemia and infective endocarditis (IE). IE is divided into acute and subacute forms, and the bacterium is isolated in subacute cases. The common symptoms are: fever, chills, sweats, anorexia, weight loss, and malaise.
''S. mutans'' has been classified into four serotypes; c, e, f, and k. The classification of the serotypes is devised from the chemical composition of the serotype-specific rhamnose-glucose polymers. For example, serotype k initially found in blood isolates has a large reduction of glucose side chains attached to the rhamnose backbone. ''S. mutans'' has the following surface protein antigens: glucosyltransferases, protein antigen and glucan-binding proteins. If these surface protein antigens are not present, then the bacteria is a protein antigen-defective mutant with the least susceptibility to phagocytosis therefore causing the least harm to cells.
Furthermore, rat experiments showed that infection with such defective ''streptococcus'' mutants (''S. mutans'' strains without glucosyltransferases isolated from a destroyed heart valve of an infective endocarditis patient) resulted in a longer duration of bacteraemia. The results demonstrate that the virulence of infective endocarditis caused by ''S. mutans'' is linked to the specific cell surface components present.
In addition, ''S. mutans'' DNA has been found in cardiovascular specimens at a higher ratio than other periodontal bacteria. This highlights its possible involvement in a variety of types of cardiovascular diseases, not just confined to bacteraemia and infective endocarditis.
Prevention and treatment
Practice of good oral hygiene
Oral hygiene is the practice of keeping one's mouth clean and free of disease and other problems (e.g. bad breath) by regular brushing of the teeth (dental hygiene) and cleaning between the teeth. It is important that oral hygiene be carried out ...
including daily brushing, flossing and the use of appropriate mouthwash can significantly reduce the number of oral bacteria, including ''S. mutans'' and inhibit their proliferation. ''S. mutans'' often live in dental plaque
Dental plaque is a biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found bet ...
, hence mechanical removal of plaque is an effective way of getting rid of them. The best toothbrushing technique to reduce plaque build up, decreasing caries risk, is the modified Bass technique. Brushing twice daily can help decrease the caries risk. However, there are some remedies used in the treatment of oral bacterial infection, in conjunction with mechanical cleaning. These include fluoride, which has a direct inhibitory effect on the enolase
Phosphopyruvate hydratase, usually known as enolase, is a metalloenzyme () that catalyses the conversion of 2-phosphoglycerate (2-PG) to phosphoenolpyruvate (PEP), the ninth and penultimate step of glycolysis. The chemical reaction is:
:2-p ...
enzyme, as well as chlorhexidine
Chlorhexidine (CHX) (commonly known by the salt forms chlorhexidine gluconate and chlorhexidine digluconate (CHG) or chlorhexidine acetate) is a disinfectant and antiseptic that is used for skin disinfection before surgery and to sterilize surgi ...
, which works presumably by interfering with bacterial adherence.
Furthermore, fluoride ions can be detrimental to bacterial cell metabolism. Fluoride directly inhibits glycolytic enzymes and H+ATPases. Fluoride ions also lower the pH of the cytoplasm. This means there will be less acid produced during the bacterial glycolysis. Therefore, fluoride mouthwashes, toothpastes, gels and varnishes can help to reduce the prevalence of caries. However, findings from investigations into the effect of fluoride-containing varnish, on the level of ''Streptococcus mutans'' in the oral environment in children suggest that the reduction of caries cannot be explained by a reduction in the level of ''Streptococcus mutans'' in saliva or dental plaque. Fluoride varnish
Fluoride varnish is a highly concentrated form of fluoride which is applied to the tooth's surface, by a dentist, dental hygienist or other health care professional, as a type of topical fluoride therapy. It is not a permanent varnish but due to ...
treatment with or without prior dental hygiene has no significant effect on the plaque and salivary levels of ''S. mutans''.
''S. mutans'' secretes Glucosyltransferase on its cell wall, which allows the bacteria to produce polysaccharides from sucrose. These sticky polysaccharides are responsible for the bacteria's ability to aggregate with one another and adhere to tooth enamel, i.e. to form biofilm
A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
s. Use of Anti Cell-Associated Glucosyltransferase (Anti-CA-gtf) Immunoglobulin Y disrupts ''S. mutans''' ability to adhere to the teeth enamel, thus preventing it from reproducing. Studies have shown that Anti-CA-gtf IgY is able to effectively and specifically suppress ''S. mutans'' in the oral cavity.
Other common preventative measures center on reducing sugar intake. One way this is done is with sugar replacements such as xylitol
Xylitol is a chemical compound with the formula , or HO(CH2)(CHOH)3(CH2)OH; specifically, one particular stereoisomer with that structural formula. It is a colorless or white crystalline solid that is freely soluble in water. It can be classifi ...
or erythritol which cannot be metabolized into sugars which normally enhance ''S. mutans'' growth. The molecule xylitol, a 5 carbon sugar, disrupts the energy production of S.mutans by forming a toxic intermediate during glycolysis. Various other natural remedies have been suggested or studied to a degree, including deglycyrrhizinated licorice root extract, tea tree oil
Tea tree oil, also known as melaleuca oil, is an essential oil with a fresh camphoraceous odor and a colour that ranges from pale yellow to nearly colourless and clear. It is derived from the leaves of the tea tree, ''Melaleuca alternifolia'', ...
, macelignan (found in nutmeg
Nutmeg is the seed or ground spice of several species of the genus ''Myristica''. ''Myristica fragrans'' (fragrant nutmeg or true nutmeg) is a dark-leaved evergreen tree cultivated for two spices derived from its fruit: nutmeg, from its seed, an ...
), curcuminoids
A curcuminoid is a linear diarylheptanoid, a relatively small class of plant secondary metabolites that includes curcumin, demethoxycurcumin, and bisdemethoxycurcumin, all isolated from turmeric (curcuma longa). These compounds are natural ph ...
(the main components of turmeric
Turmeric () is a flowering plant, ''Curcuma longa'' (), of the ginger family, Zingiberaceae, the rhizomes of which are used in cooking. The plant is a perennial, rhizomatous, herbaceous plant native to the Indian subcontinent and Southeast Asi ...
), and eugenol
Eugenol is an allyl chain-substituted guaiacol, a member of the allylbenzene class of chemical compounds. It is a colorless to pale yellow, aromatic oily liquid extracted from certain essential oils especially from clove, nutmeg, cinnamon, basil ...
(found in bay leaves, cinnamon leaves and cloves). Additionally various teas have been tested for activity against ''S. mutans'' and other dental benefits. However, none of these remedies have been subject to clinical trials or are recommended by mainstream dental health groups to treat ''S. mutans''.
The addition of bioactive glass beads to dental composite
Dental composite resins (better referred to as "resin-based composites" or simply "filled resins") are dental cements made of synthetic resins. Synthetic resins evolved as restorative materials since they were insoluble, of good tooth-like appea ...
s reduces penetration of ''Streptococcus mutans'' into the marginal gaps between tooth and composite. They have antimicrobial properties, reducing bacterial penetration. This decreases the risk of secondary caries developing, a common reason for failure of dental restoration
Dental restoration, dental fillings, or simply fillings are treatments used to restore the function, integrity, and morphology of missing tooth structure resulting from caries or external trauma as well as to the replacement of such structure sup ...
s. This means that the longevity and efficacy of composite restorations may be improved.
Survival under stressful conditions
Conditions in the oral cavity
In animal anatomy, the mouth, also known as the oral cavity, or in Latin cavum oris, is the opening through which many animals take in food and issue vocal sounds. It is also the cavity lying at the upper end of the alimentary canal, bounded on t ...
are diverse and complex, frequently changing from one extreme to another. Thus, to survive in the oral cavity, ''S. mutans'' must tolerate rapidly harsh environmental fluctuations and exposure to various antimicrobial agents to survive. Transformation
Transformation may refer to:
Science and mathematics
In biology and medicine
* Metamorphosis, the biological process of changing physical form after birth or hatching
* Malignant transformation, the process of cells becoming cancerous
* Trans ...
is a bacterial adaptation involving the transfer of DNA from one bacterium to another through the surrounding medium. Transformation is a primitive form of sexual reproduction
Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
. For a bacterium to bind, take up, and recombine exogenous DNA into its chromosome, it must enter a special physiological state termed "competence". In ''S. mutans'', a peptide pheromone quorum-sensing
In biology, quorum sensing or quorum signalling (QS) is the ability to detect and respond to cell population density by gene regulation. As one example, QS enables bacteria to restrict the expression of specific genes to the high cell densities at ...
signaling system controls genetic competence. This system functions optimally when the S. mutans cells are in crowded biofilms. ''S. mutans'' cells growing in a biofilm are transformed at a rate 10- to 600-fold higher than single cells growing under uncrowded conditions (planktonic cells). Induction of competence appears to be an adaptation for repairing DNA damage caused by crowded, stressful conditions.
Knowing about quorum-sensing gives rise to the potential development of drugs and therapies. Quorum-sensing peptides can be manipulated to cause target suicide as well as. Furthermore, quenching quorum-sensing can lead to prevention of antibiotic resistance.
Evolution
Three key traits have evolved in ''S. mutans'' and increased its virulence by enhancing its adaptability to the oral cavity: increased organic acid production, the capacity to form biofilms on the hard surfaces of teeth, and the ability to survive and thrive in a low pH environment.
During its evolution, ''S. mutans'' acquired the ability to increase the amount of carbohydrates it could metabolize, and consequently more organic acid was produced as a byproduct. This is significant in the formation of dental caries
Tooth decay, also known as cavities or caries, is the breakdown of teeth due to acids produced by bacteria. The cavities may be a number of different colors from yellow to black. Symptoms may include pain and difficulty with eating. Complicatio ...
because increased acidity in the oral cavity amplifies the rate of demineralization of the tooth, which leads to carious lesions. It is thought that the trait evolved in ''S. mutans'' via lateral gene transfer
Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offspring ( reproduction). ...
with another bacterial species present in the oral cavity. There are several genes, SMU.438 and SMU.1561, involved in carbohydrate metabolism that are up-regulated in ''S. mutans''. These genes possibly originated from ''Lactococcus lactis'' and ''S. gallolyticus'', respectively.
Another instance of lateral gene transfer is responsible for ''S. mutans acquisition of the glucosyltransferase (GTF) gene. The GTF genes found in ''S. mutans'' most likely are derived from other anaerobic bacteria found in the oral cavity, such as ''Lactobacillus'' or ''Leuconostoc''. Additionally, the GTF genes in ''S. mutans'' display homology
Homology may refer to:
Sciences
Biology
*Homology (biology), any characteristic of biological organisms that is derived from a common ancestor
* Sequence homology, biological homology between DNA, RNA, or protein sequences
*Homologous chrom ...
with similar genes found in ''Lactobacillus'' and ''Leuconostoc''. The common ancestral gene is believed to have been used for hydrolysis and linkage of carbohydrates.
The third trait that evolved in ''S. mutans'' is its ability to not only survive, but also thrive in acidic conditions. This trait gives ''S. mutans'' a selective advantage over other members of the oral microbiota. As a result, ''S. mutans'' could outcompete other species, and occupy additional regions of the mouth, such as advanced dental plaque
Dental plaque is a biofilm of microorganisms (mostly bacteria, but also fungi) that grows on surfaces within the mouth. It is a sticky colorless deposit at first, but when it forms tartar, it is often brown or pale yellow. It is commonly found bet ...
s, which can be as acidic as pH 4.0. Natural selection
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
is most likely the primary evolutionary mechanisms responsible for this trait.
In discussing the evolution of ''S. mutans'', it is imperative to include the role humans have played and the co-evolution that has occurred between the two species. As humans evolved anthropologically, the bacteria evolved biologically. It is widely accepted that the advent of agriculture in early human populations provided the conditions ''S. mutans'' needed to evolve into the virulent bacterium it is today. Agriculture introduced fermented foods, as well as more carbohydrate-rich foods, into the diets of historic human populations. These new foods introduced new bacteria to the oral cavity and created new environmental conditions. For example, ''Lactobacillus'' or ''Leuconostoc'' are typically found in foods such as yogurt and wine. Also, consuming more carbohydrates increased the amount of sugars available to ''S. mutans'' for metabolism and lowered the pH of the oral cavity. This new acidic habitat would select for those bacteria that could survive and reproduce at a lower pH.
Another significant change to the oral environment occurred during the Industrial Revolution
The Industrial Revolution was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...
. More efficient refinement and manufacturing of foodstuffs increased the availability and amount of sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
consumed by humans. This provided ''S. mutans'' with more energy resources, and thus exacerbated an already rising rate of dental caries. Refined sugar is pure sucrose, the only sugar that can be converted to sticky glucans, allowing bacteria to form a thick, strongly adhering plaque.
See also
* Mutacin 1140
* Oral microbiology
Oral microbiology is the study of the microorganisms (microbiota) of the oral cavity and their interactions between oral microorganisms or with the host. The environment present in the human mouth is suited to the growth of characteristic micro ...
* ''Streptococcus viridans
The viridans streptococci are a large group of commensal streptococcal Gram-positive bacteria species that are α-hemolytic, producing a green coloration on blood agar plates (hence the name "viridans", from Latin "vĭrĭdis", green), although ...
''
* Xylitol
Xylitol is a chemical compound with the formula , or HO(CH2)(CHOH)3(CH2)OH; specifically, one particular stereoisomer with that structural formula. It is a colorless or white crystalline solid that is freely soluble in water. It can be classifi ...
* Caries vaccine
References
External links
MCHoralhealth.org
Type strain of ''Streptococcus mutans'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q131452
Streptococcaceae
Gram-positive bacteria
Bacteria described in 1924