Objective  To observe the effect of ambroxol on the structure of Pseudomonas aeruginosa biofilm (BF) in an established biofilm model in vitro.   Method  Mature BF was formed after 7 days’ culture of Pseudomonas aeruginosa on plate. The BF structure was observed by scanning electron microscope (SEM). The parameters of BF structure were analyzed though pictures from confocal laser scanning microscopy (CLSM) with Image Structure Analyzer (ISA) software. Fluorescence intensity of the viable bacteria in BF treated by ambroxol alone and together with ciprofloxacin were determined with fluorescence microscopy.   Results  After the treatment of ambroxol

the BF was destroyed and the matrix outsides became thin and abnormal compared with the control by SEM

and small amount of bacteria dispersed. The results of ISA showed that with the treatment of 2 mg/ml ambroxol

BF was decreased in thickness

average diffusion distance (ADD) and textual entropy (TE) were decreased in comparison with the group without ambroxol treatment (P0.05)

however areal porosity (AP) was increased (P0.05). Whereas the same tendency of these parameters was seen in the group treated by 0.75 mg/ml ambroxol though not so obvious. Fluorescence microscopy indicated the viable bacteria in BF was reduced significantly (F=18

P0.05) when ambroxol concentration was higher than 0.49 mg/ml

and ambroxol showed synergistic effect when combined with ciprofloxacin (F=15.1

P0.05) in a dose-dependent manner.   Conclusion  Ambroxol can affect the BF structure of Pseudomonas aeruginosa

and thus enhance the bactericidal ability of antibiotics.