A vaccination trial using live cells of Edwardsiella tarda in tilapia

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 × 107 CFU/100 g body weight, while SPM31 had a 2.9 × 108 CFU/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 post-vaccination. 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 80 - 100% mortality. These results indicate that the live cells with lowered siderophore-production are capable of conferring protective immunity against edwardsiellosis.