Effects of Paeonol Sub-inhibitory Concentration on Streptococcus suis Biofilm and Expression of Virulence Genes

Background: Streptococcus suis is a zoonotic pathogen closely related to the respiratory tract of swine. Paeonol is a traditional Chinese medicine with antibacterial effect. This study demonstrated the effect of paeonol on biofilm formation and the expression of virulence factors of Streptococcus suis. Methods: The minimum inhibitory concentration (MIC) of paeonol on Streptococcus suis was determined by double dilution method. Crystal violet staining method was used to determine the effect of paeonol on the biofilm formation. The effects of paeonol on the morphology and structure of Streptococcus suis biofilm were observed by field emission scanning electron microscopy (FE-SEM). Real-time quantitative PCR (qRT-PCR) was used to detect the expression levels of Streptococcus suis related virulence factors under sub-MIC (1/4 MIC, 1/8 MIC) paeonol. Result: The results showed the effect of 1/4 MIC and 1/8 MIC paeonol on biofilm formation and mature biofilm was significant (*P less than 0.05). Under the action of paeonol, the biofilm structure becomes sparse. qRT-PCR results showed that 1/8 MIC paeonol inhibits bacterial adhesion by up-regulating the expression of mrp virulence genes, thereby inhibiting the formation of Streptococcus suis biofilm.