Exopolysaccharide-repressing small molecules with antibiofilm and antivirulence activity against Pseudomonas aeruginosa

Biofilm formation is a universal virulence strategy in which bacteria grow in dense microbial communities enmeshed within a polymeric extracellular matrix that protects them from antibiotic exposure and the immune system. Pseudomonas aeruginosa is an archetypal biofilm-forming organism that utilizes a biofilm growth strategy to cause chronic lung infections in cystic fibrosis (CF) patients. The extracellular matrix of P. aeruginosa biofilms is comprised mainly of exopolysaccharides (EPS) and DNA. Both mucoid and nonmucoid isolates of P. aeruginosa produce the Pel and Psl EPS, each of which have important roles in antibiotic resistance, biofilm formation, and immune evasion. Given the central importance of the EPS for biofilms, they are attractive targets for novel anti-infective compounds. In this study, we used a high-throughput gene expression screen to identify compounds that repress expression of the pel genes. The pel repressors demonstrated antibiofilm activity against microplate and flow chamber biofilms formed by wild-type and hyperbiofilm-forming strains. To determine the potential role of EPS in virulence, pel/psl mutants were shown to have reduced virulence in feeding behavior and slow killing virulence assays in Caenorhabditis elegans. The antibiofilm molecules also reduced P. aeruginosa PAO1 virulence in the nematode slow killing model. Importantly, the combination of antibiotics and antibiofilm compounds increased killing of P. aeruginosa biofilms. These small molecules represent a novel anti-infective strategy for the possible treatment of chronic P. aeruginosa infections.