Subinhibitory concentrations of Rhubarb Palmatum and its main monomers causing inhibition of alpha-hemolysin virulence in Staphylococcus aureus USA300

Abstract

The virulence of Staphylococcus aureus (S. aureus) is closely related to the production of virulence factors; thus, the treatment of S. aureus infection has become a challenging problem. Rhubarb has the characteristics of broad-spectrum antibacterial activity and drug resistance. However, the antimicrobial effects of Rhubarb and its major monomers remain unknown. In this study, the effect of Rhubarb at 1/32 and 1/64 MIC on the expression of USA300 virulence factor of Staphylococcus aureus was analyzed through transcriptome analysis. The results showed that the aqueous extract of Rhubarb significantly down-regulated the expression of USA300 virulence factors Spa, LukD, LukE, LukG, LukH and Hla at 1/32 and 1/64 MIC. The inhibitory effect of Hla was found to be the most obvious. RT-qPCR, hemolysis test, Western blot, and enzyme-linked immunosorbent assay were used to further verify the inhibitory effect of major monomers of rhubarb emodin, aloe emodin, rhein, and emodin 8–0-β-d-glucopyranoside on USA300 virulence factor α-hemolysin at sub-inhibitory concentrations. Finally, the damage degree of rhubarb monomer emodin and aloe-emodin against USA300 was confirmed in human lung epithelial cell A549, suggesting for the first time that rhubarb and its active components could inhibit the toxicity of α-hemolysin of Staphylococcus aureus, and that its anti-virulence effect may be the key to resist bacterial infection. This study provides a theoretical basis and a new strategy for the use of rhubarb in the clinical treatment of Staphylococcus aureus infection.