Quorum sensing (QS) in Aeromonas hydrophila is mainly based on the modulation of ahyI/R genes that regulates bacterial virulence determinant phenotypes. The use of QS inhibitors would be of particular interest in inhibiting bacterial pathogenicity and infections. In this study, we aimed to determine the effect of curcumin, a natural component of Curcuma longa, on the expression of QS regulating genes, ahyI and ahyR, as well as some QS regulated virulence characteristics in pathogenic fish isolated A. hydrophila strains. The minimum inhibitory concentration (MIC) of curcumin against bacteria was determined using the broth micro-dilution method and the expression of quorum sensing genes ahyI and ahyR among the bacteria treated with curcumin was determined using quantitative polymerase chain reaction (qPCR). Also, the effect of curcumin on some QS associated traits, including biofilm formation, swarming and swimming motility, proteolytic potential, and bacterial hemolytic activity was investigated. According to the results, curcumin, at a concentration of 32 µg/mL, significantly reduced the expression of both ahyI and ahyR genes among bacterial strains up to 64.2 and 91.0%, respectively. Moreover, curcumin efficiently inhibited bacterial biofilm formation, swimming, and swarming motility. Also, bacterial proteolytic activity was slightly reduced, while hemolytic activity was not significantly affected. This study demonstrated the use of curcumin to attenuate ahyI/R QS genes and several QS associated phenotypes in A. hydrophila. These findings indicate the therapeutic potential of curcumin as an anti-QS agent, to be used against A. hydrophila pathogenesis in aquaculture.
Keywords: Aeromonas hydrophila; Biofilm; Curcumin; Quorum sensing.