Alveolar epithelial injury and pleural empyema in acute P. aeruginosa pneumonia in anesthetized rabbits

We developed an experimental model of acute Pseudomonas aeruginosa pneumonia in anesthetized ventilated rabbits to determine whether bacterial-induced injury to the alveolar epithelium would occur and the effect of the injury on the pleural space. Dose-response studies established that 10(9) colony-forming units of P. aeruginosa (wild-type strain, PAO-1) were required to injure the epithelial barrier and to cause pleural empyema with exudative pleural effusions that contained both the instilled alveolar protein tracer and P. aeruginosa. We explored the mechanisms of P. aeruginosa-induced lung and pleural injury by using three isogenic bacterial strains to compare several extracellular virulence products. PAO-S21, which carries an insertion mutation in a regulatory gene that prevents the production of exoenzyme S, resulted in no lung or pleural injury. PAO-R1, which carries a deletion in a regulatory gene that controls the production of elastase and alkaline protease, caused the same degree of lung and pleural injury as PAO-1 did. Instillation of PLC-SRN, which has both structural genes encoding phospholipase C activity deleted, resulted in a moderate reduction in alveolar epithelial injury. Although other products may be involved, exoenzyme S and phospholipase C are important in mediating injury to the alveolar epithelial barrier in acute P. aeruginosa pneumonia in rabbits.