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 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 biofilms. 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 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, macelignan (found in nutmeg), curcuminoids (the main components of turmeric), and eugenol (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 composites 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 restorations. this means that the longevity and efficacy of composite restorations may be improved. survival under stressful conditions conditions in the oral cavity 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 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. 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 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. 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 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 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 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 plaques, which can be as acidic as ph 4.0. natural selection 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. more efficient refinement and manufacturing of foodstuffs increased the availability and amount of sucrose 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.