The Role of the Quorum Sensing System in a Rat Model of Pseudomonas Aeruginosa Pulmonary Infection and Its Relationship with the Expression of Virulence Factors

OBJECTIVE:A variety of in vitro experiments indicated that most of the extracellular virulence factors of Pseudomonas aeruginosa (PA) were controlled by the quorum sensing system. The aim of this study was to explore the role of the quorum sensing system in a rat model of PA pulmonary infection.METHODS:Rats were infected intratracheally with PA strain PAO1 or PAO1-JP2 (lasI rhlI double mutant) which was embedded in seaweed alginate bead. The difference of bacteriology and pathology between the two groups was compared. The in vitro activity of elastase was measured by the Congo Red method and the expression of exotoxin A was detected by Western blot.RESULTS:At the 14th and 28th days after challenge, the bacterial colony counts in the PAO1-JP2 group were (9.6 +/- 3.3) lgCFU/g and (4.2 +/- 3.1) lgCFU/g respectively; however, those of the PAO1 group were (11.3 +/- 2.8) lgCFU/g and (9.1 +/- 1.5) lgCFU/g respectively, which showed significant difference (P < 0.05). The lung index of macroscopic pathology (LIMP) and the score of macroscopic pathology of the PAO1-JP2 group were significantly lower than those of the PAO1 group at 7th, 14th and 28th days after challenge. The size of lung abscesses or granuloma in the lung under the microscope and the score of microscopic pathology of the PAO1-JP2 group were also significantly lower at the 7th, 14th and 28th days. The in vitro activity of elastase of the PAO1-JP2 strain was 0.02 +/- 0.00 and that of the PAO1 strain was 0.35 +/- 0.03, which showed significant difference (P < 0.05). The expression of exotoxin A could be detected by Western blot in the PAO1 strain but not in the PAO1-JP2 strain.CONCLUSION:When the quorum sensing system of PA was deficient the expression of some virulence factors, such as elastase and exotoxin A, were decreased, which resulted in milder pulmonary infection.