Inhibitory Effects of Ethyl Gallate on Streptococcus mutans Biofilm Formation by Optical Profilometry and Gene Expression Analysis

Abstract

This study aimed to test the effectiveness of ethyl gallate (EG) against <i>S. mutans</i> biofilm formation on solid surfaces (polystyrene, glass) and acidogenicity, and to examine the effect on expression of related genes. The biofilm that is formed by <i>S. mutans</i> bacteria was evaluated using colorimetric assay and optical profilometry, while the pH of the biofilm growth medium was measured with microelectrode. The expression of genes encoding glucan binding protein B (<i>gbpB</i>), glucosyltranferases B, -C, -D (<i>gtfB, -C, -D</i>) and F-ATPase (<i>atpD</i>, <i>atpF</i>) was assessed using a quantitative reverse transcription-polymerase chain reaction (RT-qPCR). It was revealed that all of the EG concentrations significantly suppressed <i>S. mutans</i> biofilm build-up on polystyrene and glass surfaces, and inhibited acidogenicity, in a dose-dependent manner, compared to the activity of untreated bacteria (<i>p</i> < 0.05). The highest concentration of EG (3.53 mM) reduced biofilm formation on polystyrene and glass surfaces by 68% and more than 91%, respectively, and prevented a decrease in pH levels by 95%. The RT-qPCR data demonstrate that the biofilm-producing bacteria treated with EG underwent significant gene expression changes involving the <i>gtfC</i> (a 98.6 increase in fold change), <i>gtfB</i> gene (a 47.5 increase in fold change) and the <i>gbpB</i> gene (a 13.8 increase in fold change). However, for the other genes tested (<i>gtfD</i>, <i>atpD</i> and <i>atpF</i>), the EG treatments did not produce significant expression change compared to the control. EG produced significant gene expression change in three genes-<i>gtfC,</i> <i>gtfB</i>, and <i>gbpB</i>; it has the capacity to inhibit <i>S. mutans</i> biofilm formation on solid surfaces (polystyrene, glass), as well as acidogenicity. Therefore, EG might be used as an antibiofilm and/or anticaries agent for oral formulations in order to reduce the prevalence of dental caries.