Cinnamaldehyde Decreases the Pathogenesis of Aeromonas hydrophila by Inhibiting Quorum Sensing and Biofilm Formation

Antibiotics were the main fishery drugs for treatingAeromonas hydrophila(A. hydrophila) infection, which would generate selective pressure and result in the appearance of antibiotic-resistant bacteria. The bacterial quorum sensing (QS) system provides a new alternative strategy againstA. hydrophilainfection. QS inhibitors can reduce bacterial virulence behaviors by disrupting QS, which has no effect on bacterial growth. Therefore, we studied the effect of cinnamaldehyde from a natural plant extract on the QS ofA. hydrophilaaiming to reduce its pathogenicity. The efficacy of cinnamaldehyde againstA. hydrophilawas evaluated from various aspects, including the effects on aerolysin, lipase, protease, swarming motility, biofilm formation, acyl-homoserine lactones (AHLs), and QS-related genes. Moreover, the therapeutic effect of cinnamaldehyde in vitro and in vivo was studied. The results showed that cinnamaldehyde could decrease the virulence phenotypes ofA. hydrophilaregulated by QS. Moreover, the transcriptions of related genes (aerA,ahyR, andahyI) were downregulated following the addition of cinnamaldehyde. The in vitro and in vivo therapeutic assays show that cinnamaldehyde could reduce the aerolysin-mediated A549 cell injury and increase the survival rate of crucian carp infected withA. hydrophila. These results indicate that cinnamaldehyde would be a candidate QS inhibitor againstA. hydrophilainfection.Keywords:Aeromonas hydrophila;quorum sensing;cinnamaldehyde;virulence;biofilm