Sucrose challenges to Streptococcus mutans biofilms and the curve fitting for the biofilm changes

The relationship between sugar level and development of dental caries has long been a main topic in dentistry. However, as a ubiquitous component of the modern diet, sucrose is mainly derived from three meals a day, rather than a long time exposure. In this study, various concentrations of sucrose were provided to Streptococcus mutans biofilms for 1 h per exposure (three times per day) to imitate a human meal pattern. And then the relationship between sucrose concentration and changes in the treated biofilms was determined. The results indicated that the components and acid production of the treated biofilms changed in a second-order polynomial curve pattern with sucrose concentration increase, which were confirmed by CLSM and SEM analyses. However, gene expression related to extracellular polysaccharides (EPS) formation, acid production and tolerance was up-regulated with sucrose concentration increase, which might have been due to compensation for the decrease in EPS formation and acid production by the biofilms at higher concentrations of sucrose. These findings suggest that sucrose in the range of 1%-5% can support the highest acid production and accumulation of S. mutans biofilms, which may further increase its cariogenic potential. However, additional studies are required to confirm the relationships in human cariogenic biofilms.