Elimination of multidrug resistant plasmid pEIB202 in fish pathogenic Edwardsiella tarda.

[Objective] The aim of the research was to investigate the function of large plasmid pEIB202 in in the pathogenesis of Edwardsiella tarda EIB202 and eliminate the plasmid pEIB202,so as to lay the foundation for developing safe and live attenuated 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 suggested that the plasmid might be related with the multiple drug-resistance and pathogenicity of E.tarda.The plasmid-eliminated strain EIB202Δp lost the resistance to chloramphenicol and tetracycline,but its growth,virulence and secretion of extracellular proteins had no significant difference with wild-type plants.[Conclusion] pEIB202 plasmid was the main reasons that caused the multi-drug resistance of EIB202 and might have indirect effects in the pathogenesis of EIB202.