Intervene effect on Streptococcus suis biofilm formation of emodin extracted from Rheum officinale Baill

Abstract Background Streptococcus suis is a zoonotic pathogen that causes serious systemic infections in pigs and humans. It is a great threat to pig breeding and public health safety. The formation of biofilm was one of the main reasons that it’s difficult to cure. Rhubarb water extract can inhibit the formation of biofilm of Streptococcus suis, but the main functional ingredient was not clear. And what’s the potential mechanism of emodin intervene the biofilm formation? Importantly, the gene expression of luxS of Streptococcus suis was significantly decreased with emodin treatment, if there is a possibility that emodin could combine with LuxS protein which in turn inhibit the formation of biofilm? Methods Optimization of green ultrasonic extraction of emodin from R. officinale by Response Surface Methodology. The activity of antibacterial was evaluated by MIC assay. And the ability that intervene biofilm formation was evaluated through Crystal violet staining and SEM. The combination mode between emodin and LuxS protein was identified through molecular docking. Results The optimum extraction conditions (ethanol concentration of 80%, extraction time of 21 min, and liquid to solid ratio of 12.5:1 mL/g) were determined through the interaction analysis of different influencing factors and model verification experiment. The minimal inhibitory concentration (MIC) of RUEP against S.suis was 15.625 µg·mL-1, and sub-inhibitory concentrations of RUEP (1/2, 1/4, 1/8 and 1/16 MIC) significantly inhibited the biofilm formation of S. suis. Moreover, scanning electron microscopy analysis confirmed that RUEP can damage the layered colony community structure in biofilm and effectively intervene in the biofilm formation of Streptococcus suis. Through molecular docking analyzed, the inhibition of biofilm formation could be realized through the formation of hydrogen bond with residues His14 and Glu 60, π-π staking with His61、Phe80 and hydrophobic interaction with Cys127. Conclusion Through our study, we found emodin have good antibacterial and antibiofilm formation properties and the potential mechanism of emodin intervention on biofilm formation of Streptococcus suis was inferred.