Search for live attenuated vaccine candidate against edwardsiellosis by mutating virulence-related genes of fish pathogen Edwardsiella tarda

Aims: The aims of this study were to construct and evaluate the live attenuated vaccine against edwardsiellosis on zebra fish model. Methods and Results: In this study, the deletion mutant of aroC gene for the biosynthesis of chorismic acid in Edwardsiella tarda EIB202 was firstly constructed by allelic exchange strategy. According to the genome information, 19 double mutants and one multiple mutant were successively constructed by deleting virulence-associated genes based on the Delta aroC mutant. Zebra fish model was used to assay the virulence of the mutants by intramuscular (i.m.) injection. Fourteen mutants were significantly attenuated with accumulated mortality ranged from 0 to 63% (P < 0.05). The zebra fish vaccinated with Delta aroC, Delta aroC Delta esrC, Delta aroC Delta slyA and Delta aroC Delta eseBCD Delta esaC via i.m. injection showed ideal protection, resulting in relative per cent survival (RPS) of 68.3, 71.3, 80.1 and 81% against subsequent challenge with the wild-type Edw. tarda EIB202. Conclusions: Delta aroC Delta eseBCD Delta esaC behaved a low virulence and the highest RPS on zebra fish model. When the zebra fish were vaccinated with Delta aroC Delta eseBCD Delta esaC via injection, the expression of immune-related factors including IgM and MHC II was up-regulated. Significance and Impact: The mutant Delta aroC Delta eseBCD Delta esaC might serve as an effective live attenuated vaccine against edwardsiellosis.