A genotypic and phenotypic comparison of type III secretion profiles of Pseudomonas aeruginosa cystic fibrosis and bacteremia isolates

The type III secretion system (TTSS) of Pseudomonas aeruginosa enables delivery of a number of toxins involved in the disruption of eukaryotic epithelial surfaces. Whilst the ability to secrete ExoS facilitates invasion and internalization, the secretion of ExoU mediates acute cytotoxicity. In order to determine any association with the ability to secrete these toxins with the nature and severity of human infection, the TTSS genotypes and phenotypes of 163 clinical isolates were determined by multiplex PCR and Western blotting. An exoS+/exoU- genotype was associated with chronic infection in patients with cystic fibrosis whilst an exoS-/exoU+ genotype was associated with strains isolated from blood. Secretion of the ExoU protein was more commonly seen in isolates obtained from blood, suggesting this ability may be important in the development of acute invasive infection. Detection of TTSS toxins in clinical material may be useful in targeting antimicrobial therapy or identifying individuals infected with aggressive strains of P. aeruginosa.