The Immune Strategy In Prevention Of Edwardsiellasis In Turbot (Scophthalmus Maximus)

Edwardsiella tarda is a severe aquaculture pathogen that can infect many fshspecies and cause a systematic disease called edwardsiellosis, which can lead to highmortality under certain conditions. In this paper, two kinds of vaccine named subunitvaccine rFimA, and avirulence divalent strain P1V3were constructed and selected forthe prevention of edwardsiellosis effectively.A mutant strain of E. tarda which fimA was knocked out was constructed by themethod of in-frame deletion. Compared to the wild strain TX01, the mutant strainTXfimA had a lower ability in forming biofilm, impaired ability to disseminate intohost tissues following experimental infection and attenuated infectivity against hostcells. These results indicate that FimA is an important virulence factor. To examinewhether rFimA possess immunogenicity property, recombinate FimA was expressedand extracted in vitro. After vaccination turbot with rFimA for one month and thenchallenged with E. tarda, group vaccinated with rFimA gained great protectionagainst E. tarda with RPS of71.9%. Another experiment showed that although rFimAshowed no protection on turbot against Vibrio harveyi infection, it enhanced subunitvaccine rVhhP2protection efficiency after V. harveyi challenge. This means thatrFimA not only has the potential of being an effective subunit vaccine, but alsopossess adjuvant effect.To solve the constrained usage of subunit vaccine, in this paper we alsoconstructed immersion and oral feeding vaccine of P1SW, V3SW andP1V3(combination of P1SW and V3SW).16sRNA sequence analysis showed thatP1SW and V3SW belong to the genera of Pseudomonas and Vibrio respectively. After vaccination turbot with monovalent P1SW, V3SW or divalent P1V3throughimmersion and oral feeding for one month, and then challenged with E. tarda and V.anguillarum, group vaccinated with monovalent P1SW showed protection against E.tarda challenge with RPS of42.4%; monovalent V3SW group showed protectionagainst both E. tarda and V. anguillarum challenge with RPS of48.5%and58.1%respevctively; While divalent P1V3group exhibited protection against both E. tardaand V. anguillarum challenge to the extend that was significantly higher thanmonovalent P1SW and V3SW with RPS of78.8%and93.5%. These results indicatethat P1V3is a good avirulence divalent vaccine which is hopefully to be used in theprevention of E. tarda and V. anguillarum infection.In conclusion FimA is an important virulence factor in E. tarda, and plays animportant role in the process of infection. rFimA has a good potential as a subunitvaccine, and possess adjuvant effect. Divalent vaccine P1V3induces significantlyelevated and effective cross-protection against both E. tarda and V. anguillarum.Therefore vaccine rFimA and P1V3have great potential in control of edwardsiellasisin the future.