Antibacterial effect of ursolic acid incorporated in composite resin on Streptococcus mutans

Abstract

I. Objectives The objective of this study was to evaluate the in vitro antibacterial effect of the composite resins containing ursolic acid.II. Materials and Methods Composite resins with three different concentrations (0.1, 0.2 and 0.5 wt%) of ursolic acid (U6753, Sigma Aldrich, St. Louis, MO, U.S.A.) were prepared with acetone. The composite resin mixed only with acetone served as a negative control. Flexural strength was measured based upon the ISO 4049 standards. Either glucose or sucrose was used as carbohydrate source, and for different saliva treatment, the sterilized specimens were submerged in unstimulated whole saliva (UWS) or phosphate-buffered saline (PBS) for 2 hours prior to experiment. For biofilm assay, composite resin disk specimen was then transferred to S. mutans suspension and incubated for 24 hours. Afterwards, the specimens were rinsed with PBS and sonicated for 90 seconds. The colony forming unit of the disrupted biofilm cultures were evaluated for viable cell counting. For growth inhibition test, the resin specimens were placed on a polystyrene well cluster, and S. mutans suspension in trypton-vitamin medium was inoculated. The OD600 was recorded by Infinite® F200 pro apparatus (TECAN, Salzburg, Austria). Two-way ANOVA following Bonferroni correction was used for the data analyses.III. Results The flexural strength values did not show statistically significant difference at any concentration (P >0.01). In biofilm assay, the CFU value decreased as the concentration of ursolic acid increased. The influence of saliva pretreatment was conflicting. The groups where sucrose was provided as nutrient exhibited significantly higher CFU score than those provided with glucose. In growth inhibition test, most experimental groups resulted in a complete inhibition of bacterial growth regardless of the concentration of ursolic acid.IV. Conclusions Antimicrobial tests using S. mutans showed that ursolic acid, when incorporated in dental composite resins at low concentration (0.1-0.5 wt%) exhibited an antibacterial effect against S. mutans for the experimental periods. Within the limitations of this experimental conditions, ursolic acid included in the composite showed inhibition of biofilm formation and S.mutans growth.