Objective       To determine the inhibitory effect of different sub-inhibitory concentrations of ceftazidime on the biofilm formation of the clinically isolated stains of Escherichia coli and investigate the underlying mechanism in this process.       Methods       The minimum inhibitory concentrations (MIC) of 15 antibiotic agents on Escherichia coli 46 (E46) was tested by the agar double dilution method according to the Performance Standards for Antimicrobial Susceptibility Testing (2010 Edition) by Clinical and Laboratory Standards Institute (CLSI). PCR was used to detect the expression of the genes related to superspectrum β-lactamases (ESBLs). Furthermore

high efficiency liquid chromatography (HPLC) was used to analyze the change of the concentrations of ceftazidime in the inhibition of E46 during its biofilm formation.       Results       E46 was only sensitive to imipenem

meropenem

ami-kacin and macrodantin

and resistant to ceftazidime and other 8 agents. Ceftazidime in the range of 1/2MIC to 1/16MIC inhibited biofilm formation of E46 in a dose-dependent manner (P0.05). E46 carried TEM and CTX-M-15 enzymes

and the concentration of ceftazidime was gradually decreased in inhibiting the biofilm formation.       Conclusion       The sub-inhibitory concentration of ceftazidime inhibits the biofilm formation of the clinical drug resistant strain E46

but its concentration is significantly degraded over time.