| Objective To explore the effect of Pseudomonas aeruginosa biofilm on the production of P -lactamase induced by imipenem and ceftazidime.Methods The P.aeruginosa strain PA01 was used in this study. In vitro models of Pseudomonas aeruginosa bacterial biofilm were built up in eppendorf tube and a rapid staining procedure of crystal violet was used to verify them. The formation of biofilm was confirmed under light microscope.The test was developed under two groups, planktonic and biofilm bacteria of Pseudomonas aeruginosa. They were exposed to different concentrations of imipenem and ceftazidime for 4h. The expression of P -lactamase was detected using the chromogenic-lactam, nitrocefin and quantitated by a spectrophotometric assay method. P -Lactamase quantitative analysis was determined by using the Folin-Phenol protein assay. The class of P -lactamase was verdicted by the improved Cefoxitin three-dimensional test.Results In the absence of the inducer,both the biofilm and planktonic bacteria have no the detectable activity of P -lactamase, whereas the level of induction in the presence of adequate levels of imipenem or ceftazidime was significant. The planktonic bacteria produced the maximum level of P -lactamase when exposed to 2 mg/L of imipenem,and the biofilm bacteria to 16 mg/L. The two maximal value were different significantly with the statistic methed of t test (P<0.05) . There are no detectable levels of P -lactamase expression below the ceftazidime 1/2 MIC (2mg/L),but even sub-MICs of imipenem down to 0.2mg/L, the expression of P -lactamase at ample levels were clearly detectable. The improved Cefoxitin three-dimensional test showed the P -lactamase induced was AmpC P -lactamase.Conclusion With the induction of some antibiotics, planktonic and biofilm bacteria of Pseudomonas aeruginosa have a different ability in the production of P -lactamase, and the biofilm bacteria are induced more easily. Imipenem induced the expression of ampC much more potently than ceftazidime.
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