Abstract
This study was conducted to evaluate if extracellular polysaccharides (EPS) are used by Streptococcus mutans (Sm) biofilm during night starvation, contributing to enamel demineralization increasing occurred during daily sugar exposure. Sm biofilms were formed during 5 days on bovine enamel slabs of known surface hardness (SH). The biofilms were exposed to sucrose 10% or glucose + fructose 10.5% (carbohydrates that differ on EPS formation), 8x/day but were maintained in starvation during the night. Biofilm samples were harvested during two moments, on the end of the 4th day and in the morning of the 5th day, conditions of sugar abundance and starvation, respectively. The slabs were also collected to evaluate the percentage of surface hardness loss (%SHL). The biofilms were analyzed for EPS soluble and insoluble and intracellular polysaccharides (IPS), viable bacteria (CFU), biofilm architecture and biomass. pH, calcium and acid concentration were determined in the culture medium. The data were analyzed by two-way ANOVA followed by Tukey’s test or Student's t-test. The effect of the factor carbohydrate treatment for polysaccharide analysis was significant (p < 0.05) but not the harvest moment (p > 0.05). Larger amounts of soluble and insoluble EPS and IPS were formed in the sucrose group when compared to glucose + fructose group (p < 0.05), but they were not metabolized during starvation time (S-EPS, p = 0.93; I-EPS, p = 0.11; and IPS = 0.96). Greater enamel %SHL was also found for the sucrose group (p < 0.05) but the demineralization did not increase during starvation (p = 0.09). In conclusion, the findings suggest that EPS metabolization by S. mutans during night starvation do not contribute to increase enamel demineralization occurred during the daily abundance of sugar.
Highlights
Dental caries is a biofilm-sugar related disease that depends on biofilm accumulation on tooth surface and its frequent exposure to dietary carbohydrates [1]
The amounts of intracellular (IPS), and soluble (S-EPS) and insoluble (I-EPS) extracellular polysaccharides in biofilms formed under daily exposure to sucrose were higher, when compared to those found in biofilms exposed to glucose + fructose (Fig 1) (p < 0.05)
The biofilm dry weight was much higher when the biofilm was formed under sucrose exposure than those formed with glucose + fructose (p < 0.05), and no significant change was observed after overnight starvation
Summary
Dental caries is a biofilm-sugar related disease that depends on biofilm accumulation on tooth surface and its frequent exposure to dietary carbohydrates [1]. The cariogenic biofilm forms and grows on dental surfaces in a dynamic condition in which the exposure to dietary carbohydrates occurs intermittently [2]. Exopolysaccharides degradation and enamel demineralization the meals and overnight. These episodes are known as "feast" and "famine" periods and they are determinant for bacterial metabolism and biofilm growth [3, 4, 5]. In “feast” periods, bacterium such as S. mutans is able to store the excess of available carbohydrate as intracellular polysaccharides (IPS), which act as an energy reserve source in “famine” periods [6, 7]. Besides the IPS storage, glucosyl- and fructosyltransferases enzymes produced by S. mutans synthesize extracellular polysaccharides (EPS) when sucrose is the available carbohydrate [8, 9, 10]
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