Pseudomonas aeruginosa mutations in lasl and rhll quorum sensing systems result in milder chronic lung infection

To understand the importance of quorum sensing in chronic Pseudomonas aerug inosa lung infection, the in vivo pathogenic effects of the wild-type P aer uginosa PAO1 and its double mutant, PAO1 lasI rhlI, in which the signal-gen erating parts of the quorum sensing systems are defective were compared. Th e rat model of P. aeruginosa lung infection was used in the present study. The rats were killed on days 3, 7, 14 and 28 after infection with the P. ae ruginosa strains. The results showed that during the early stages of infect ion, the PAO1 double mutant induced a stronger serum antibody response, hig her production of pulmonary interferon gamma, and more powerful blood polym orphonuclear leukocyte (PMN) chemiluminescence compared to its wild-type co unterpart. On days 14 and 28 post-infection, significantly milder lung path ology, a reduction in the number of mast cells present in the lung foci, a reduced number of lung bacteria, and minor serum IgG and IgG1 responses but increased lung interferon gamma production were detected in the group infe cted with the PAO1 double mutant when compared with the PAO1-infected group . Delayed immune responses were observed in the PAO1-infected group and the y might be associated with the production of virulence factors that are con trolled by the quorum sensing systems. The conclusion of this study is that functional lasI and rhlI genes of P, aeruginosa PAO1 play a significant ro le during lung infection.