Role of intestinal inflammation in predisposition of Edwardsiella tarda infection in zebrafish (Danio rerio)

• The impact of intestinal inflammation was described on Edwardsiella tarda infection.
• Zebrafish with intestinal inflammation were more susceptible to E. tarda.
• E. tarda colonized easily in tissues of zebrafish with intestinal inflammation.
• E. tarda induced more intense acute immune responses of the sick zebrafish.
• Antibacterial responses inhibit the growth of commensals that E. tarda could resist.

Edwardsiella tarda, an enteric opportunistic pathogen, is associated with acute to chronic edwardsiellosis in cultured fish, resulting in heavy losses in aquaculture. To date, the pathogenesis of E. tarda has been extensively studied and a great deal of vaccine candidates have been attempted. However, the research on the predisposition of E. tarda infection is poorly reported. In this study, the effects of intestinal inflammation on E. tarda infection were investigated using a zebrafish model that influenced by perturbation of intestinal microbiota. Featured symptoms of edwardsiellosis were observed in intestinal inflammatory zebrafish compared with healthy fish. Higher bacterial numbers were detected in both mucosal tissues (intestine, skin and gills) and lymphoid tissues (liver, spleen and kidney) of inflammatory zebrafish while the bacterial loads in healthy zebrafish appeared to be relatively lower by 10–100 folds. Moreover, significant up-regulation of IL-1β, TNF-α and iNOS was noticed in multiple tissues of zebrafish with intestinal inflammation between 6 and 72 h post infection. However, only moderate elevation was observed in the gills and liver of healthy fish. Furthermore, the expression of genes involved in neutrophil recruitment (mpx, IL-8 and LECT2) and antimicrobial response (β-defensin and hepcidin) showed notable up-regulation in the intestine of inflammatory zebrafish. These results demonstrate that fish with intestinal inflammation is more susceptible to E. tarda and the antimicrobial response during E. tarda infection might inhibit the growth of intestinal microbiota. Our results suggest that maintaining good management to avoid intestinal inflammation is a feasible prevention measure against edwardsiellosis.