Effect of <i>Radix Paeoniae Rubra</i> aqueous extract on the virulence and antibiotic susceptibility of multi-drug resistant <i>Escherichia coli</i>

Abstract Introduction Some traditional Chinese medicine herbs can be used for the treatment of infectious diseases; however, the mechanisms are not fully explored. This study aims to elucidate the mechanism of action of Radix Paeoniae Rubra , one of the most commonly used herbs, in bacterial infections by studying its effects on the resistance and pathogenicity of multi-drug resistant (MDR) bacteria. Material and Methods In this study, MDR Escherichia coli O101 was treated with Radix Paeoniae Rubra aqueous extract (RPRE), and then the virulence factor protein secretion, biofilm formation and the drug resistance-related gene expression were determined by using broth microdilution, ELISA and qPCR. Results Our results found that RPRE inhibited the bacterial virulence factor proteins. It suppressed the antibiotic-induced transcription increase of efflux pump genes marA and soxS . It inhibited not only the expression of the outer membrane porin genes ompC and ompF but also the formation of bacterial biofilms, and the combination of RPRE with antibiotics increased the bacteria’s sensitivity to them. Conclusion Our study demonstrated that RPRE alone has a slight inhibitory effect on the bacteria, but at its sub-inhibitory concentrations, it can reduce resistance-related gene expression, inhibit virulence factor protein production and suppress biofilm formation. Furthermore, RPRE forms a bactericidal efficacy synergy when combined with antibiotics by decreasing MDR E. coli resistance and pathogenicity.