Prevention of edwardsiellosis in channel catfish, Ictalurus punctatus, by constructed live attenuated vaccines

Protection of channel catfish against edwardsiellosis, one of the most significant problems affecting its industry, was the aim of this study. This was achieved by using live attenuated vaccines. E. piscicida C07-087, the recently identified cause of edwardsiellosis in fish farms, was used for constructing five mutants (EpssaV, EpesaM, EpyscR, EpesaS and EpescT) by deleting five genes encoding structural proteins in the type III secretion system (T3SS) apparatus. The mutants were phenotypically characterized and their immune response, tissue persistence, virulence and efficacy as vaccines via immersion and intraperitoneal injection (i.p.) routes were evaluated. Three of the constructed mutants; EpssaV, EpyscR and EpesaS were significantly attenuated. Vaccination by i.p. injection using two different doses of the constructed mutants was more significantly effective. Intraperitoneally vaccinated Channel catfish with high doses of EpesaM, EpyscR and EpescT showed zero mean percent mortality when challenged with E. piscicida WS. In addition, the cross-protection afforded by the previously prepared live attenuated E. ictaluri vaccine, ESC-NDKL1, against edwardsiellosis caused by E. piscicida C07-087 was investigated. Fish vaccinated with ESC-NDKL1 via immersion for one hour showed high level of antibodies and several E. piscicida immunogenic proteins were identified. In addition, all challenged fish with E. piscicida WS were protected opposite to 40% morality in non-vaccinated fish. In conclusion, ESC-NDKL1 vaccine is preferable as it protects channel catfish against edwardsiellosis and enteric septicemia of catfish and is easily applied.