Sensitivity of Streptococcus mutans for fluoride

Objectives: Streptococcus mutans is considered to be the principal causative agent of dental caries and fluoride materials are the most used chemical agent for controlling the disease. We meet sometimes children who have decayed teeth in spite of using home fluoride materials for prevention of caries routinely. This situation is usual reported by their guardian. We predict that fluoride doesn't work enough. There is possibility that they have some fluoride-resistant Streptococcus mutans. It was reported that enolase is very sensitive to fluoride, and inhibition of this enzyme can result in a reduction of sugar uptake as well as glycolysis. Our aim is to investigate that how different sensibility of enolase in relation to fluoride some standard strains have. Methods: We selected 5 different Streptococcus mutans strains.LM-7, C69-1, UA159, UA130 and NCH105. NCH105 is reported as fluoride-resistant mutant strain. We evaluated about 4 items: (1) 5 strains were checked growth in BHI with different concentration NaF. (2) Carbohydrate metabolism of strains were determined with api50 CH (bioMérieux). (3) Permiabilized cells were made and enolase activities were investigated. (4) Genetic sequences of enolase were compared across strains. Results: Growth of S.mutans was suppressed on fluoride concentration- dependence. Degree of suppression was not the same of each strain.UA 130 and NCH105 were more resistant than other strains in growth. Metabolism types of carbohydrates on each strain were similar but not the same. Fluoride suppressed their metabolism and there was no fluoride specific carbohydrate. Enolase activities used permeabilized cells were not indicated same tendency of growth. Gene analysis exposed UA130 and NCH105 had a point mutation at different area, so they had different amino acid. Conclusion: It was shown there is possibility that some strains have mutant enolase. It would appear that enolase mutation is one of factor associated with fluoride sensitivity.