title: The Role of ExoS in Dissemination of Pseudomonas aeruginosa during Pneumonia.
abstract: Hospital-acquired pneumonia is associated with high rates of morbidity and mortality, and dissemination to the bloodstream is a recognized risk factor for particularly poor outcomes. Yet the mechanism by which bacteria in the lungs gain access to the bloodstream remains poorly understood. In this study, we used a mouse model of Pseudomonas aeruginosa pneumonia to examine this mechanism. P. aeruginosa uses a type III secretion system to deliver effector proteins such as ExoS directly into the cytosol of eukaryotic cells. ExoS, a bi-functional GTPase activating protein (GAP) and ADP-ribosyltransferase (ADPRT), inhibits phagocytosis during pneumonia but has also been linked to a higher incidence of dissemination to the bloodstream. We used a novel imaging methodology to identify ExoS intoxicated cells during pneumonia and found that ExoS is injected into not only leukocytes but also epithelial cells. Phagocytic cells, primarily neutrophils, were targeted for injection with ExoS early during infection, but type I pneumocytes became increasingly injected at later time points. Interestingly, injection of these pneumocytes did not occur randomly but rather in discrete regions, which we designate ""fields of cell injection" (FOCI). These FOCI increased in size as the infection progressed and contained dead type I pneumocytes. Both of these phenotypes were attenuated in infections caused by bacteria secreting ADPRT-deficient ExoS, indicating that FOCI growth and type I pneumocyte death were dependent on the ADPRT activity of ExoS. During the course of infection, increased FOCI size was associated with enhanced disruption of the pulmonary-vascular barrier and increased bacterial dissemination into the blood, both of which were also dependent on the ADPRT activity of ExoS. We conclude that the ADPRT activity of ExoS acts upon type I pneumocytes to disrupt the pulmonary-vascular barrier during P. aeruginosa pneumonia, leading to bacterial dissemination.
authors.affiliation: Departments of Microbiology/Immunology, Feinberg School of Medicine, Northwestern Univesity, Chicago, Illinois, United States of America.
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Rangel
authors.affiliation: Departments of Microbiology/Immunology, Feinberg School of Medicine, Northwestern Univesity, Chicago, Illinois, United States of America.
authors.forename: Maureen H
authors.initials: MH
authors.lastname: Diaz
authors.affiliation: Departments of Microbiology/Immunology, Feinberg School of Medicine, Northwestern Univesity, Chicago, Illinois, United States of America.
authors.forename: Claire A
authors.initials: CA
authors.lastname: Knoten
authors.affiliation: Departments of Microbiology/Immunology, Feinberg School of Medicine, Northwestern Univesity, Chicago, Illinois, United States of America.
authors.forename: Angelica
authors.initials: A
authors.lastname: Zhang
authors.affiliation: Departments of Microbiology/Immunology, Feinberg School of Medicine, Northwestern Univesity, Chicago, Illinois, United States of America; Department of Medicine, Feinberg School of Medicine, Northwestern University, Chicago, Illinois, United States of America.
authors.forename: Alan R
authors.initials: AR
authors.lastname: Hauser
mesh_terms: D036002:ADP Ribose Transferases / Q000378:metabolism*; D000818:Animals; D016470:Bacteremia / Q000378:metabolism / Q000473:pathology*; D001427:Bacterial Toxins / Q000378:metabolism*; D004195:Disease Models, Animal; D018450:Disease Progression; D005260:Female; D005434:Flow Cytometry; D007049:Iatrogenic Disease; D051379:Mice; D008807:Mice, Inbred BALB C; D018410:Pneumonia, Bacterial / Q000378:metabolism / Q000473:pathology*; D011552:Pseudomonas Infections / Q000378:metabolism / Q000473:pathology*; D011550:Pseudomonas aeruginosa
chemical_list: D001427:Bacterial Toxins; D036002:ADP Ribose Transferases; C444820:exoenzyme S