OBJECTIVES: In this study, the destabilizing effect of glycyrrhetinic acid on pre-formed biofilms of Streptococcus mutans (S. mutans) was observed. METHODS: Alamar blue assay was used to determine the toxicity of glycyrrhetinic acid on pre-formed biofilms of S. mutans. Four different concentrations (0, 3.75, 7.5, 15 µg/ml) of glycyrrhetinic acid were tested. Changes in the biofilm architecture after exposure to glycyrrhetinic acid were analyzed by scanning electron microscopy (SEM). Moreover, the role of glycyrrhetinic acid in enhancing the antimicrobial activity of cetylpyridinium chloride (CPC), an antimicrobial agent commonly used in oral health care products, was evaluated. RESULTS: Glycyrrhetinic acid concentration of up to 15 µg/ml had little cytotoxic effect but significantly changed the biofilm architecture. SEM analysis revealed destabilized biofilm structure after the preformed biofilms were exposed to glycyrrhetinic acid. Supplementing 2.5 µg/ml CPC with 15 µg/ml glycyrrhetinic acid significantly enhanced the bactericidal effect of CPC on the pre-formed biofilms than that in the non-supplemented CPC treated control. This indicates that glycyrrhetinic acid enhanced the antimicrobial activity of CPC by modifying the structure, thus facilitating the penetration of CPC into the biofilm. CONCLUSIONS: Glycyrrhetinic acid could be a potential agent to effectively control S. mutans biofilms responsible for dental caries.
Biofilms* ; Cetylpyridinium ; Dental Caries ; Glycyrrhetinic Acid* ; Microscopy, Electron, Scanning ; Oral Health ; Streptococcus mutans* ; Streptococcus*

OBJECTIVES: The present study aimed at investigating the potential of using 18β-glycyrrhetinic acid against the cariogenic characteristics of Streptococcus mutans UA159. METHODS: The effects of 18β-glycyrrhetinic acid on biofilm formation and acid production were evaluated; the latter are indicators of cariogenicity of S. mutans. Biofilm architecture was also analyzed by scanning electron microscopy (SEM), and changes in gene expression related to biofilm formation were studied by quantitative RT-PCR. RESULTS: Treatment with 18β-glycyrrhetinic acid at a concentration of 20 µg/ml inhibited biofilm formation by 95% in the absence of sucrose and 60% in its presence, reduced acid production by 88.8%, and significantly suppressed the gene expression of comDE, gbpB, gtfC and vicR, which are thought to be involved in the virulence of S. mutans. CONCLUSIONS: These results suggest that 18β-glycyrrhetinic acid could be used as a complementary or alternative agent for preventing dental caries by interfering with the virulence properties of S. mutans without affecting the viability of the bacterial population.
Biofilms ; Dental Caries ; Gene Expression ; Microscopy, Electron, Scanning ; Streptococcus mutans ; Streptococcus ; Sucrose ; Virulence