Objective To investigate the effect of phillyrin on virulence factors of Streptococcus mutans. Methods Streptococcus mutans bacterial solution was divided into 8 g/L phillyrin group, 4 g/L phillyrin group, 2 g/L phillyrin group, 1 g/L phillyrin group, 0.5 g/L phillyrin group, 0.25 g/L phillyrin group, or 0.125 g/L phillyrin group. The corresponding concentration of phillyrin was added to each group. Simultaneously, negative control group (without medication, containing only bacterial solution and BHIS medium), blank control group (adding only BHIS medium), solvent control group (adding dimethyl sulfoxide, bacterial solution and BHIS medium, with the final concentration of dimethyl sulfoxide in 5%), and positive control group (adding chlorhexidine, bacterial solution and BHIS medium, with the final concentration of chlorhexidine in 0.2%) were set up. The adhesion and acid production abilities of Streptococcus mutans in various groups were compared. Streptococcus mutans bacterial solution was further assigned to 2 g/L phillyrin group (adding 2 g/L phillyrin as the final concentration) or negative control group (without medication, containing only bacterial solution and BHIS medium). The morphology and structure of Streptococcus mutans biofilm, the relative expression of virulence genes glucosyltransferase (GTF)B, GTFC and GTFD, and the demineralization depth of bovine enamel were compared between the two groups. Results Compared with the negative control group, the adhesion of Streptococcus mutans in the 8 g/L phillyrin group, 4 g/L phillyrin group, 2 g/L phillyrin group, 1 g/L phillyrin group, 0.5 g/L phillyrin group, 0.25 g/L phillyrin group, 0.125 g/L phillyrin group and positive control group decreased. Compared with the 0.125 g/L phillyrin group, 0.25 g/L phillyrin group, 0.5 g/L phillyrin group, and 1 g/L phillyrin group, the adhesion of Streptococcus mutans in the 4 g/L phillyrin group, 8 g/L phillyrin group, and positive control group was even lower (P<0.05). The results of scanning electron microscope revealed that the morphology and structure of Streptococcus mutans biofilm in the negative control group were intact. Streptococcus mutans biofilm in the 2 g/L phillyrin group was sparse and thinner, and the structure was loose, which could not form a three-dimensional structure. Compared with the negative control group, the mRNA expressions of Streptococcus mutans biofilm virulence genes GTFB, GTFC and GTFD, and the demineralization depth of bovine enamel were decreased in the 2 g/L phillyrin group (P<0.05). Compared with the negative control group, the acid production ability of Streptococcus mutans were decreased in the 8 g/L phillyrin group, 4 g/L phillyrin group, 2 g/L phillyrin group, 1 g/L phillyrin group, 0.5 g/L phillyrin group, 0.25 g/L phillyrin group, 0.125 g/L phillyrin group and positive control group. The acid production ability of Streptococcus mutans gradually decreased with the increase of phillyrin concentration (P<0.05). Conclusion Phillyrin can inhibit the adhesion, acid production and demineralization abilities of Streptococcus mutans, reduce the expression of its virulence genes, and destroy the morphology and structure of Streptococcus mutans biofilm.

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