Pseudomonas aeruginosa cystic fibrosis isolates induce rapid, type III secretion-dependent, but ExoU-independent, oncosis of macrophages and polymorphonuclear neutrophils

Pseudomonas aeruginosa, an opportunistic pathogen responsible most notably for severe infections in cystic fibrosis (CF) patients, utilizes the type I II secretion system for eukaryotic cell intoxication. The CF clinical isola te CHA shows toxicity towards human polymorphonuclear neutrophils (PMNs) wh ich is dependent on the type III secretion system but independent of the cy totoxin ExoU. In the present study, the cytotoxicity of this strain toward human and murine macrophages was demonstrated. In low-multiplicity infectio ns (multiplicity of infection, 10), approximately 40% of the cells die with in 60 min. Analysis of CHA-infected cells by transmission electron microsco py, DNA fragmentation assay, and Hoechst staining revealed the hallmarks of oncosis: cellular and nuclear swelling, disintegration of the plasma membr ane, and absence of DNA fragmentation. A panel of 29 P. aeruginosa CF isola tes was screened for type III system genotype, protein secretion profile, a nd cytotoxicity toward PMNs and macrophages. This study showed that sis CF isolates were able to induce rapid ExoU-independent oncosis on phagocyte ce lls.