Abstract: The relationship between the drug resistance of duck E.coli and extended-spectrum β-lactamases, was analyzed to provide the laboratory theoretical basis for clinical therapy. Preliminary screening test and phenotype confirmatory test recommended by CLSI were used to detect the production of extended-spectrum β-lactamases (ESBLs) in 12 strains of clinical duck E.coli, micro-double dilution was carried out to determine the antibacterial activity of 9 antimicrobials (Ciprofloxacin). The results indicated that 4 of 12 isolates product ESBLs, accounting for 33%. The strains with ESBLs-producing had resistances to many kinds of antimicrobials,had crossing resistances to fluoroquinolones (FQNs) and had multidrug resistances to fluoroquinolones (FQNs), aminoglycosides and cephalosporins (CEPs). The resistance of ESBLs-producing strains was higher than non-ESBLs-producing strains significantly. ESBLs-producing was one of the major mechanism that duck E.coli formed resistances.

Key words: duck E.coli; ESBLs; drug susceptibility; micro-double dilution; resistance