The exoenzyme S regulon of Pseudomonas aeruginosa

Pseudomonas aeruginosa can cause severe life-threatening infections in which the bacterium disseminates rapidly from epithelial colonization sites to the bloodstream. In experimental models, the ability of P. aeruginosa to disseminate is linked to epithelial injury, in vitro cytotoxicity and expression of the exoenzyme S regulon. Using the expression of ExoS as a model, a series of genes that are important for regulation, secretion and, perhaps, intoxication of eukaryotic cells have been identified. Proteins encoded by the exoenzyme S regulon and the Yersinia Yop virulon show a high level of amino acid homology, suggesting that P. aeruginosa may use a contact-mediated translocation mechanism to transfer anti-host factors directly into eukaryotic cells. Potential anti-host factors that may disrupt eukaryotic signal transduction through ADP-ribosylation include ExoS and ExoT. Expression of ExoU, another candidate anti-host factor, has been correlated with acute cytotoxicity and lung epithelial injury. Members of the exoenzyme S regulon represent only a portion of the virulence factor arsenal possessed by P. aeruginosa. It will be important to understand how the exoenzyme S regulon contributes to pathogenesis and whether these factors could serve as potential therapeutic targets.