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

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