Type III protein secretion is associated with death in lower respiratory and systemic Pseudomonas aeruginosa infections

The ability of Pseudomonas aeruginosa to secrete specific toxins using the type III-mediated pathway has been reported. To determine the association o f this phenotype with human illness, immunoblot analysis was used to detect expression of type III secretory proteins in P. aeruginosa isolates from r espiratory tract or blood cultures of 108 consecutive patients. Relative ri sk of mortality was 6-fold greater with expression of the type III secretor y proteins ExoS, ExoT, ExoU, or PcrV. Phenotype was independently correlate d with toxicity in cellular and murine models. Prevalence of this phenotype was significantly higher in acutely infected patients than in chronically infected patients with cystic fibrosis. These results suggest that the type III protein secretion system is integral to increased P. aeruginosa virule nce. A positive phenotype is a predictor of poor clinical outcome. In the f uture, such analyses may help distinguish potentially lethal infection from colonization and help determine appropriate therapy for critically ill pat ients.