Abstract: ObjectiveTo understand whether the strong virulent plasmid of Shigella can transfer in vitro and still possess pathogenicity after the transfer.MethodsHuman Shigella flexneri and the large virulent plasmid of Shigella were separately mixed with chicken Shigella boydii,and then cultured at 37℃ and 4℃ refrigerator for 24 hours.Chickens and mice were experimentally infected either orally or intraperitoneally with transferred-strain of large plasmid in different dosages.ResultsThe strong virulent plasmid of human Shigella was successfully transferred into chicken Shigella boydii which had lost the large virulence plasmid.Chicken and mice inoculated with transferred-strain showed pathogenicity of the strains transferred.The culture characteristics of transferred-strain was changed.ConclusionThe strong virulent plasmid of Shigella in a suitable environment can be transferred in to pathogenic bacteria in the close category in vitro and the new transfered-strain possessed certain stability and pathogenicity.The high pathogenicity of Shigella would occured if there were strong virulent plasmid and other special causative agents of bacteria simultaneously.