Suppressive Effects of Octyl Gallate on Streptococcus mutans Biofilm Formation, Acidogenicity, and Gene Expression

Abstract

The accumulation of biofilm by Streptococcus mutans bacteria on hard tooth tissues leads to dental caries, which remains one of the most prevalent oral diseases. Hence, the development of new antibiofilm agents is of critical importance. The current study reports the results from testing the effectiveness of octyl gallate (C8-OG) against: (1) S. mutans biofilm formation on solid surfaces (polystyrene, glass), (2) acidogenicity, (3) and the expression of biofilm-related genes. The amount of biofilm formed by S. mutans bacteria was evaluated using the colorimetric method and optical profilometry. The pH of the biofilm growth medium was measured with microelectrode. A quantitative reverse transcription-polymerase chain reaction (RT-qPCR) was used to assess the expression of genes encoding glucan binding protein B (gbpB), glucosyltransferases B, -C, -D (gtfB, -C, -D), and the F-ATPase β subunit of the F1 protein (atpD). The results show that C8-OG significantly diminished biofilm formation by exposed S. mutans on solid surfaces and suppressed acidogenicity in a dose-dependent manner, compared to unexposed bacteria (p < 0.05). The C8-OG concentration of 100.24 µM inhibited S. mutans biofilm development on solid surfaces by 100% and prevented a decrease in pH levels by 99%. In addition, the RT-qPCR data demonstrate that the biofilm-producing bacteria treated with C8-OG underwent a significant reduction in gene expression in the case of the four genes under study (gbpB, gtfC, gtfD, and atpD), and there was a slight decrease in expression of the gtfB gene. However, C8-OG treatments did not produce significant expression change compared to the control for the planktonic cells, although there was a significant increase for the atpD gene. Therefore, C8-OG might be a potent antibiofilm and/or anticaries agent for oral formulations that aim to reduce the prevalence of dental caries.

Lauryl Gallate Activity and Streptococcus mutans: Its Effects on Biofilm Formation, Acidogenicity and Gene Expression

“…Moreover, DMSO alone, used at a concentration of 0.67%, had an insignificant effect against S. mutans biofilm development relative to that of the control bacteria (p > 0.05). Interestingly, the biofilm-inhibiting concentrations of C12-LG were in a quite narrow range, reflecting a similar finding for octyl gallate, that suppressive concentrations fell into a range from 97.4 to 100.24 µM [29]. However, this inhibitory effect of C12-LG occurred at lower concentrations than those of octyl gallate, and it was markedly greater than the activity of ethyl and methyl gallates, for which previously determined suppressive concentrations were in the ranges of 2.78-3.53 and 2.99-5.43 mM, respectively [27,28].…”

“…Among these natural compounds, epigallocatechin-3-gallate (EGCG), a major polyphenol in green tea (Camellia sinensis), also found in many other plants, has shown inhibitory effects against Streptococcus mutans [26]. In our previous studies, other natural derivatives of alkyl gallates that have been shown to significantly suppress S. mutans biofilm formation are methyl gallate (C1-MG) and ethyl gallate (C2-EG) [27,28], and we have demonstrated that an octyl gallate derivative (C8-OG) significantly diminished biofilm formation and suppressed the associated genes expressed in S. mutans [29]. Alkyl gallates with longer alkyl chains, e.g., the derivative lauryl gallate (dodecyl gallate), have yet to be investigated for these actions on biofilm formation and its related genes in S. mutans.…”

Correlation between Antibacterial Activity and Free-Radical Scavenging: In-Vitro Evaluation of Polar/Non-Polar Extracts from 25 Plants

“…Our next study will aim to discover novel and highly active natural antibacterial products, using a novel in-house bioassay guided fractionation approach [1,28,31,37] and in-silico based modeling techniques [29,[47][48][49][50] to identify natural products that exhibit antibacterial activity against S. mutans.…”

“…One hundred µL, corresponding to 5 × 10 5 CFU/mL, was added to all the wells. The plates were incubated at 37 • C for 24 h. For more details regarding the cultivation condition, see our recent publications [1,37]. Tetracycline was used as a positive control for S. mutans.…”

“…The antibacterial IC 50 for each plant extract was determined by extracting the value from the equation of the linear part of the graph. The negative control was DMSO solvent and, as reported in previous publications [1,37], its minimum inhibitory concentration (MIC) value is 25% (v/v).…”