Aeromonas hydrophila can modulate synchronization of immune response in gut-liver axis of red crucian carp via the breach of gut barrier

The survival of farmed fish can be threatened by incidence of Aeromonas hydrophila infection. In addition, gut infection may promote dysbiosis of gut flora and dysregulate immune response in gut-liver axis in teleost fish. The current study aimed to evaluate the pathogenesis of A. hydrophila on gut barrier breach and synchronized immune response in gut-liver axis of RCCs. RCCs were subjected to continuous anal-intubation with A. hydrophila. Midgut sections were stained with periodic acid-Schiff (PAS) and immune-related gene expressions and biochemical indices in gut-liver axis were investigated. The severe midgut injury was detected in RCC anal-intubated with A. hydrophila, along with atrophy of the midgut villi, and the expression levels of tight junction (TJ) genes were consistently lower than those of the control (P < 0.05). Moreover, RCC receiving anal intubation with A. hydrophila showed the upregulation of pathological indices and immure genes in the midgut and liver. These findings demonstrated that gut infection with A. hydrophila can significantly disrupt epithelial permeability to exacerbate gut barrier breach and increase bacterial burdens in tissues as well as dysregulate immune response in gut-liver axis of RCC.