Abstract
In this study, we conducted a vaccination trial using live attenuated cells of Edwardsiella tarda in tilapia Oreochromis niloticus. A mutant strain (SPM31) with lowered siderophore production was constructed from a wild-type E. tarda FPC498 using transposon Tn5. FPC498 had a calculated LD50 of 1.8 ×107CFU/100 g body weight, while SPM31 had a 2.9×108CFU/100 g body weight. Formalin-killed cells or live bacteria of SPM31 were intraperitoneally injected to tilapia at a dose of 0.1 mg/100 g (about one third of the LD50 value) for vaccination. Both the formalin-killed and the live cells activated the antibody production. The vaccinated fish were challenged with the parent strain FPC498 at the 2nd, 3rd and 4th weeks of postvaccination. There were no deaths due to the challenge with the bacterium in the fish immunized with the live cells. On the contrary, the vaccination with formalin-killed cells resulted in 80100% mortality. These results indicate that the live cells with lowered siderophore-production are capable of conferring protective immunity against edwardsiellosis.
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