ObjectiveTo examine the effect of Pseudomonas aeruginosa on intestinal barrier function and its lethal potential when introduced into the intestinal tract of mice. Summary Background DataThe mere presence of P. aeruginosa in the intestinal tract of critically ill patients is associated with a threefold increase in death compared with matched cohorts without this pathogen. Whether this effect is a cause or a consequence of the critically ill state has not been previously addressed. MethodsTransepithelial electrical resistance, a measure of tight junction permeability, was evaluated in Caco-2 intestinal epithelial cells cells apically inoculated with live P. aeruginosa, exotoxin A, or purified PA-I lectin, an adhesin of P. aeruginosa. Lethality studies to P. aeruginosa were carried out in mice undergoing 30% surgical hepatectomy by injecting the bacteria or its various components directly into the cecum.