Objective   To study the mechanism of multiple-antibiotic-resistance in clinical isolates of Shigella and to detect the distribution and expression of active efflux pump gene acrAB-tolC.

  Methods   Distributions of acrAB-tolC in clinical isolates of Shigella were determined by PCR-SSCP and the levels of acrAB-tolC expression were defermined by Northern-blots.

  Results   acrAB-tolC was found in the all strains; the lack of genes was not foud.The mutation of tolC gene was found in four multiple-antibotic-resistance(Mar)of Shigella and the mutation of tolC gene in one susceptible strains; the mutation of acr B gene was not found.The expression level of acrA gene in the Mar strains was significantly higher than that in the susceptible strains; the mutation of acrB gene was not found.The expression level of acrA gene in the Mar strains was significantly higher than that in the susceptible strains(P > 0.05).

  Conclusion   High expression of acrA gene leads to multiple-antbiotic-resistance in clinical isolates of Shigella, and Mar operon may contribute to the regulation of acrAB-tolC gene expression.