Modulation of Streptococcus mutans Biofilm and Virulence by a Natural Compound

Abstract

Objectives: Current oral antimicrobial agents are primarily broad-spectrum bactericides. They lack effectiveness in modulating biofilms and inhibiting its virulence. Stilbenoids are naturally occurring plant phenolic compounds with a wide variety of biological activities. The objective of this study was to identify a natural stilbenoid to modulate biofilms of Streptococcus mutans, the principal cariogenic bacterial species. Methods: Five common stilbenoids (resveratrol, piceatannol, gnetol, pterostilbene, piceid) were screened for their antibacterial activity against S.mutans (UA159, the genome sequence reference strain) using standard microbiological assays. The most effective stilbenoid was used for further investigations against S.mutans biofilms, using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM), lactic acid production and structure-activity relationship by molecular docking. Water was used as the control. Statistical analysis was performed using one-way ANOVA (P=0.05). Results: The biofilm inhibitory concentrations of resveratrol, pterostilbene and piceatannol were 65.2, 54.1 and 12.7 μg/mL respectively. Gnetol and piceid did not inhibit the biofilms. Hence, piceatannol was chosen for further investigations. SEM and CLSM analyses revealed that 5 minutes of treatment with piceatannol (12.7 μg/mL) disrupted the biofilm integrity and significantly altered the architecture of pre-formed 48h S.mutans biofilm, without any bacterial killing. Water had no effect on the biofilms. Lactic acid production was significantly decreased by piceatannol (0.4 mmol/L), compared to the water control (0.8 mmol/L) (P<0.05).Molecular docking analysis predicted that piceatannol can bind to the LuxS pocket of S.mutans, suggesting anti-quorum sensing potential. Conclusions: Piceatannol is highly effective against Streptococcus mutans biofilm and its virulence (acidogenicity). The disruption of LuxS quorum sensing system by piceatannol is currently under investigation.