Objective   To study the effects of ambroxol on the signal molecules N-acyl-homoserinelactone (AHL) of quorum-sensing (QS) system in Pseudomonas aeruginosa biofilm (BF) and on the expressions of AHL synthase encoding genes in an established biofilm model in vitro.   Methods   BF formation in the mature Pseudomonas aeruginosa BF model

established after plate culture for 7 d

was identified by scanning electron microscopy (SEM). After the treatment of ambroxol at different concentrations

the effects of ambroxol on the mRNA expressions of AHL synthase encoding genes rhl I and las I were detected by quantitative real-time RT-PCR; the AHL signal molecules were quantified by AHL-responsive Agrobacterium tumefaciens reporter strain.   Results   After the treatment of ambroxol at the concentration of 3.75 mg/ml

the mRNA expression of rhlI and lasI were down-regulated significantly as compared with the control group (P0.05); AHL level was also lower than that in the control group (P0.01). Ambroxol at the concentration of 1.875 mg/ml had the same tendency as at the concentration of 3.75 mg/ml

but not so obvious (P0.05).   Conclusion   Ambroxol can inhibit the BF forming activity by means of down-regulation of the expressions of AHL synthase encoding genes and the AHL signal molecules of quorum-sensing system in Pseudomonas aeruginosa biofilm.