Regulation of virulence factors of Pseudomonas aeruginosa by Scutellaria baicalensis, Prunella vulgaris and antimicrobial peptide LL-37.

Introduction. The increasing resistance and the pathogen's complex multi-drug resistance mechanisms made the selection of effective antimicrobial treatments more challenging for Pseudomonas aeruginosa (P. aeruginosa). The study aimed to explore the effect of Scutellaria baicalensis, Prunella vulgaris and antimicrobial peptide LL-37 on the virulence factors of P. aeruginosa.Hypothesis. Previous studies have shown that extracts from traditional Chinese medicines, Scutellaria baicalensis and Prunella vulgaris, can also enhance the effects of antibiotics and reduce antibiotic resistance in P. aeruginosa. Antimicrobial peptide LL-37 shows the potential as a new-generation candidate for treating multi-drug-resistant bacteria, which has advantages over traditional antibiotics, whilst the combination role between Scutellaria baicalensis, Prunella vulgaris and LL-37 in P. aeruginosa remains unknown.Aim. We explored whether the combined use of Scutellaria baicalensis, Prunella vulgaris and LL-37 can exert antibacterial effects through the quorum sensing (QS) system.Methodology. The minimal inhibitory concentrations of Scutellaria baicalensis, Prunella vulgaris and LL-37 were determined for PAO1 and PA-ΔlasI/rhlI using micro broth dilution. The antibacterial activity of Scutellaria baicalensis combined with LL-37 and Prunella vulgaris combined with LL-37 was also assessed. The growth abilities of PAO1 were analysed after being treated with Scutellaria baicalensis, Prunella vulgaris and LL-37, respectively. Elastase secretion was measured using Congo red-elastic proteinase assays. And the expressions of QS genes (lasI, rhlR) were analysed by real-time PCR.Results. Single or combined treatments of Scutellaria baicalensis and LL-37 and Prunella vulgaris and LL-37 would significantly reduce elastase secretion. There were no significant differences in proliferation between the groups at any timepoint. All treatments downregulated lasI and rhlR gene expressions.Conclusion. Scutellaria baicalensis, Prunella vulgaris and antimicrobial peptide LL-37 all down-regulate the QS system-related genes of P. aeruginosa, inhibiting the secretion of virulence factors and reducing bacterial toxicity.