Coumarin Reduces Virulence and Biofilm Formation in Pseudomonas aeruginosa by Affecting Quorum Sensing, Type III Secretion and C-di-GMP Levels

Abstract

As one of the major pathogens in wound infections, <i>Pseudomonas aeruginosa</i> produces several virulence factors and forms biofilms; these processes are under the regulation of various quorum sensing (QS) systems. Therefore, QS has been regarded as a promising target to treat <i>P. aeruginosa</i> infections. In the present study, we evaluated the effect of the plant-derived QS inhibitor coumarin on <i>P. aeruginosa</i> biofilms and virulence. Coumarin inhibited QS in the <i>P. aeruginosa</i> QSIS2 biosensor strain, reduced protease and pyocyanin production, and inhibited biofilm formation in microtiter plates in different <i>P. aeruginosa</i> strains. The effects of coumarin in inhibiting biofilm formation in an <i>in vitro</i> wound model and reducing <i>P. aeruginosa</i> virulence in the <i>Lucilia sericata</i> infection model were strain-dependent. Transcriptome analysis revealed that several key genes involved in the <i>las, rhl, Pseudomonas</i> quinolone signal (PQS), and integrated QS (IQS) systems were downregulated in coumarin-treated biofilms of <i>P. aeruginosa</i> PAO1. Coumarin also changed the expression of genes related to type III secretion and cyclic diguanylate (c-di-GMP) metabolism. The cellular c-di-GMP level of <i>P. aeruginosa</i> PAO1 and recent clinical <i>P. aeruginosa</i> strains was significantly reduced by coumarin. These results provide new evidence for the possible application of coumarin as an anti-biofilm and anti-virulence agent against <i>P. aeruginosa</i> in wound infections.