Abstract: AIM: To study the inhibitory and scavenging effects of ambroxol combined with levofloxacin on the bacterial biofilm of Klebsiella pneumoniae, and to provide a new strategy to treat and antagonize the formation of the biofilm. METHODS: We collected Klebsiella pneumoniae of different resistance and divided them into sensitive group (wild bacteria group), ESBLs group and CRKP group with 15 strains in each group and performed biological semi-quantitative detection of its biofilm by crystalline violet staining method. After selecting 3 strains with similar membrane yields from each group, we determined the minimum inhibitory concentration (MIC) of ambroxol and levofloxacin against Klebsiella pneumoniae by micro broth dilution method.In addition, we determined the effects of ambroxol in different concentrations on the MIC of levfloxacin by the micrdilution checkerboard techniques and calculated the partial inhibitory concentration index (FIC) to determine the joint effect and select the best synergistic concentration. Finally, the effects of ambroxol and levofloxacin in different concentrations on the inhibition formation test and removal test of Klebsiella pneumoniae biofilm were observed by crystal violet method combined with confocal laser scanning microscopy. RESULTS: We found that all three groups of bacterial biofilms became mature on the 5th day, and the sensitive group was easier to form and produce biofilm more than the ESBLs and CRKP groups (F=3.725, P=0.032). It was showed that the geometric average of levofloxacin MIC value in the three groups decreased significantly. And the selected strains all showed a synergistic effect on the two-drug combination.In the biofilm test, as the concentration of ambroxol increased, its inhibition rate reached more than 75%, but its biofilm removal rate did not reach 70%. CONCLUSION: Our study support that ambroxol combined with levofloxacin can inhibit the bacterial biofilm of Klebsiella pneumoniae early, and its optimal synergistic concentration is 0.49 mg/mL (ambroxol) + 4 μg/mL (levofloxacin).

Key words: Klebsiella pneumoniae, ambroxol, levofloxacin, biofilm