Objective      To study the effect of sub-minimal inhibitory concentration (sub-MIC) of ceftazidime on biofilm formation of Escherichia coli (E. coli) isolated from urethral catheters and provide the rational information to use antibiotics.       Methods      The MIC was determined by agar double dilution assay. Extended-spectrum β-lactamases (ESBLs) were detected by double-disk synergy test. The adhesion of E. coli was analyzed using flat colony counting

and the biofilm formation was assayed using 96-well crystal violet staining.       Results      E. coli strains isolated from the urethral catheters had high resistance to ampicillin

cefoperazone

cefotaxime and piperacillin

and were sensitive to amikacin

imipenem and meropenem. The ESBL-producing E. coli strains accounted for 73.3%. The biofilm formation of E. coli could be inhibited with 1/4 MIC of ceftazidime

and the biofilm formation capacity decreased by 8.7%-58.0%. The sub-MIC of ceftazidime inhibited the biofilm formation of other 14 strains (P0.05) except E. coli E11 and E15 (P0.05). The sub-MIC of ceftazidime could inhibit adhesion of E. coli isolates.       Conclusion      The sub-MIC of ceftazidime can inhibit the biofilm formation of E. coli isolated from the urethral catheters

but the inhibitive effect varies in different strains.