Pseudomonas aeruginosa Effector ExoS Inhibits ROS Production in Human Neutrophils

Cell Host Microbe. 2017 May 10;21(5):611-618.e5. doi: 10.1016/j.chom.2017.04.001.


Neutrophils are the first line of defense against bacterial infections, and the generation of reactive oxygen species is a key part of their arsenal. Pathogens use detoxification systems to avoid the bactericidal effects of reactive oxygen species. Here we demonstrate that the Gram-negative pathogen Pseudomonas aeruginosa is susceptible to reactive oxygen species but actively blocks the reactive oxygen species burst using two type III secreted effector proteins, ExoS and ExoT. ExoS ADP-ribosylates Ras and prevents it from interacting with and activating phosphoinositol-3-kinase (PI3K), which is required to stimulate the phagocytic NADPH-oxidase that generates reactive oxygen species. ExoT also affects PI3K signaling via its ADP-ribosyltransferase activity but does not act directly on Ras. A non-ribosylatable version of Ras restores reactive oxygen species production and results in increased bacterial killing. These findings demonstrate that subversion of the host innate immune response requires ExoS-mediated ADP-ribosylation of Ras in neutrophils.

Keywords: T3SS; effector function; keratitis; type III secretion.

MeSH terms

  • ADP Ribose Transferases / antagonists & inhibitors*
  • ADP Ribose Transferases / metabolism
  • ADP-Ribosylation / drug effects
  • Animals
  • Bacterial Toxins / antagonists & inhibitors*
  • Bacterial Toxins / immunology
  • Colony Count, Microbial
  • Epithelium / pathology
  • Eye / pathology
  • Female
  • GTPase-Activating Proteins / antagonists & inhibitors
  • Humans
  • Immunity, Innate
  • Mice, Inbred C57BL
  • NADPH Oxidases / metabolism
  • Neutrophils / enzymology
  • Neutrophils / immunology*
  • Neutrophils / metabolism*
  • Phagocytosis
  • Phosphatidylinositol 3-Kinases / metabolism
  • Pseudomonas Infections / immunology*
  • Pseudomonas Infections / microbiology
  • Pseudomonas aeruginosa / immunology
  • Pseudomonas aeruginosa / metabolism*
  • Pseudomonas aeruginosa / pathogenicity
  • Reactive Oxygen Species / metabolism*
  • Signal Transduction / drug effects
  • Survival Analysis
  • Type III Secretion Systems / drug effects
  • ras Proteins / drug effects*
  • ras Proteins / metabolism


  • Bacterial Toxins
  • ExoT protein, Pseudomonas aeruginosa
  • GTPase-Activating Proteins
  • Reactive Oxygen Species
  • Type III Secretion Systems
  • NADPH Oxidases
  • ADP Ribose Transferases
  • exoenzyme S
  • ras Proteins