Disruption of the quorum sensing regulated pathogenic traits of the biofilm-forming fish pathogen Aeromonas hydrophila by tannic acid, a potent quorum quencher.

The quorum sensing (QS) phenomenon regulates a myriad of pathogenic traits in the biofilm forming fish pathogen, Aeromonas hydrophila. Blocking the QS mechanism of A. hydrophila is a novel strategy to prevent disease in fish. This study evaluated the effect of tannic acid, a QS inhibitor, on A. hydrophila-associated QS regulated phenomena. A streaking assay with Chromobacterium violaceum (CVO26) reported the presence of N-acyl homoserine lactone (AHL) in A. hydrophila, which was confirmed by HPLC and GC-MS analysis. Tannic acid-treated A. hydrophila showed a considerable reduction in violacein production, blood haemolysis activity and the pattern of swarming motility. Biofilm formation was significantly reduced (p < 0.001) (up to 95%), after tannic acid treatment for 48 h. Analysis by qRT-PCR revealed significant downregulation (p < 0.001) of AhyI and AhyR transcripts in A. hydrophila after tannic acid treatment. Co-stimulation of Catla catla with A. hydrophila and tannic acid attenuated pathogen-induced skin haemorrhages and increased the relative survival rate up to 86.6%. The study provides a mechanistic basis of tannic acid as a QS blocker and indicates its therapeutic potential against A. hydrophila-induced pathogenesis.