Abstract: Objective　To study the potential gene mutation increasing the drug resistance ability of emrE efflux pumpvia genetic modification of the emrE gene from clinical isolated Shigella spp.stra in H24,and to investigate the relationship between clinical drugresistance development of Shigella spp.and the vertical evolution of emrE efflux pump.Methods Gene emrE was mutated viaerror prone PCR.Drugres is tance of the strain was determined by microdilution growth curve method.The expression of the genes was measured by fluorescent quantitative RT-PCR and the bioinformatics analysis was conducted by DNAS tar.Results Among the 31 mutants,ep2-emrE showed the ability of increasing tetracyc line and ery thromyc in res is tance and the newly gained ability of chlorom ycetinres is tance indicating the mutational potent of the gene.Conclusion Although it is easy for gene emrE to achieve new drug resistant ability,the mutation and vertical evolution of the emrE gene is not selected in the development of tetracyc line and eryth romyc in resistance.So,there may be some more strong multid rug resis tance genes and mutation.