Anti-virulence properties of plant species: Correlation between in vitro activity and efficacy in a murine model of bacterial infection

Abstract

Several plant extracts exhibit anti-virulence properties due to the interruption of bacterial quorum sensing (QS). However, studies on their effects at the preclinical level are scarce. Here, we used a murine model of abscess/necrosis induced by Pseudomonas aeruginosa to evaluate the anti-pathogenic efficacy of 24 plant extracts at a sub-inhibitory concentration. We analyzed their ability to inhibit QS-regulated virulence factors such as swarming, pyocyanin production, and secretion of the ExoU toxin via the type III secretion system (T3SS). Five of the seven extracts with the best anti-pathogenic activity reduced ExoU secretion, and the extracts of Diphysa americana and Hibiscus sabdariffa were identified as the most active. Therefore, the abscess/necrosis model allows identifica-tion of plant extracts that have the capacity to reduce pathogenicity of P. aeruginosa. Furthermore, we evaluated the activity of the plant extracts on Chromobacterium violaceum. T3SS (∆escU) and QS (∆cviI) mutant strains were assessed in both the abscess/necrosis and sepsis models. Only the ∆escU strain had lower pathogenicity in the animal models, although no activity of plant extracts was observed. These results demonstrate differences between the anti-virulence activity recorded in vitro and pathogenicity in vivo and between the roles of QS and T3S systems as virulence determinants.