Harmine acts as a quorum sensing inhibitor decreasing the virulence and antibiotic resistance of Pseudomonas aeruginosa

As antimicrobial resistance (AMR) has become a global health crisis, new strategies against AMR infection are urgently needed. Quorum sensing (QS), responsible for bacterial communication and pathogenicity, is among the targets for anti-virulence drugs that thrive as one of the promising treatments against AMR infection. We identified a natural compound, Harmine, through virtual screening based on three QS receptors of Pseudomonas aeruginosa (P. aeruginosa) and explored the effect of Harmine on QS-controlled and pathogenicity-related phenotypes including pyocyanin production, exocellular protease excretion, biofilm formation, and twitching motility of P. aeruginosa PA14. The protective effect of Harmine on Caenorhabditis elegans (C. elegans) and mice infection models was determined and the synergistic effect of Harmine combined with common antibiotics was explored. The underlaying mechanism of Harmine's QS inhibitory effect was illustrated by molecular docking analysis, transcriptomic analysis, and target verification assay. In vitro results suggested that Harmine possessed QS inhibitory effects on pyocyanin production, exocellular protease excretion, biofilm formation, and twitching motility of P. aeruginosa PA14, and in vivo results displayed Harmine's protective effect on C. elegans and mice infection models. Intriguingly, Harmine increased susceptibility of both PA14 and clinical isolates of P. aeruginosa to polymyxin B and kanamycin when used in combination. Moreover, Harmine down-regulated a series of QS controlled genes associated with pathogenicity and the underlying mechanism may have involved competitively antagonizing autoinducers' receptors LasR, RhlR, and PqsR. This study shed light on the anti-virulence potential of Harmine against QS targets, suggesting the possible use of Harmine and its derivates as anti-virulence compounds.