[Objective] The aim of the research was to investigate the function of large plasmid pEIB202 in the pathogenesis of Edwardsiella tarda EIB202 and to eliminate the plasmid pEIB202,so as to lay the foundation for developing safe and live attenu- ated vaccine against E, tarda. [Method] sacB was used as reverse screening marker to eliminate the plasmid by using homologous recombination technique. [Result] The plasmid pEIB202 was sequenced and it was found that the plasmid encoded multiple resistant genes and some components in type IV secretion system（T4SS）,which sug- gested that the plasmid might be related with the multiple drug-resistance and pathogenicity of E. tarda. The plasmid-eliminated strain EIB202Ap lost the resistance to chloramphenicol and tetracycline,but its growth,virulence and secretion of extra- cellular proteins had no significant difference with wild-type plants. [Conclusion] pEIB202 plasmid is the main reason that caused the multi-drug resistance of EIB202 and might have indirect effects in the pathogenesis of EIB202.
