Abstract: To explore the relationship between antimicrobial-resistance phenotypes and the destruction of β-lactamases, the active efflux system, cell membrane permeability,observed the change of duck source E.coli antimicrobial sensitivity with or without Sulbactam, Reserpine, EDTA. The minimal inhibitory concentrations (MIC) of Ceftiofur sodium, Enrofloxacin, Amikacin, Florfenical, Doxycycline with or without Sulbactam,Reserpine, EDTA to duck source E.coli were determined by broth microdilution. There were separately five strains sensitivity increase significantly when Sulbactam combine with Ceftiofur sodium;while Reserpine had apparent effect on three strains to Ceftiofur sodium. EDTA had obvious function on the strains to all antimicrobial, there were 7,5,3,6,8 strains showed positive separately; when used Sulbactam and Reserpine at the same time, five strains sensitivity increased significantly if combined with Ceftiofur sodium and four with Florfenical. The isolates were significantly positive after added Sulbactam, Reserpine, EDTA simultaneously and five categories antimicrobial of MIC decreaseed obviously. The reason of duck source E.coli antibiotic resistance contains changes in cell membrane permeability, the active efflux system and the destruction role of β-lactamases, which combined improved the resistance level of duck source E.coli. The change in cell membrane permeability was the most important role in this study.

Key words: duck source E.coli; multi-resistance; β-lactamase inhibitors; active efflux pump; membrane permeability