The sub-inhibitory concentration of cinnamaldehyde resists Aeromonas hydrophila pathogenicity via inhibition of W-pili production

Aeromonas hydrophila is one of the most important pathogens of zoonotic importance globally, causing various diseases in humans and animals. With the increase of drug resistance and the emergence of multidrug-resistant strains, therapeutic effects of antibiotics against A. hydrophila are limited. Hence, novel agents and strategies are urgently needed to overcome these difficulties. Wavy pili (W-pili), one of the major adhesion molecules, play a crucial role in adhesion and hemagglutination in the pathogenesis of A. hydrophila and regarded as a potential target for therapy. In this study, cinnamaldehyde, a natural compound isolated from cinnamon, could inhibit the production of W-pili and its biological function at the sub-inhibitory concentration (sub-MIC). To determine the active mechanism of cinnamaldehyde, transmission electron microscopy, adhesion inhibition, hemagglutination, electrophoresis, semi-quantitative RT-PCR, biofilm assay, and fish immersion challenge were performed. The results showed that cinnamaldehyde can reduce the production of W-pili and the formation of biofilm without affecting the growth of A. hydrophila . Besides, cinnamaldehyde interfered with the synthesis of W-pili by downregulating the expression of the genes related to pili protein, thereby reducing the adhesion and hemagglutination ability of A. hydrophila and its adhesive ability to the gills and intestines of channel catfish. Therefore, cinnamaldehyde could be employed as a promising candidate for preventing and controlling A. hydrophila infection in aquaculture, especially in antibiotic-resistant strains.