Neutrophil Extracellular Trap (NET)-mediated Killing of Pseudomonas Aeruginosa: Evidence of Acquired Resistance Within the CF Airway, Independent of CFTR

PLoS One. 2011;6(9):e23637. doi: 10.1371/journal.pone.0023637. Epub 2011 Sep 1.

Abstract

The inability of neutrophils to eradicate Pseudomonas aeruginosa within the cystic fibrosis (CF) airway eventually results in chronic infection by the bacteria in nearly 80 percent of patients. Phagocytic killing of P. aeruginosa by CF neutrophils is impaired due to decreased cystic fibrosis transmembrane conductance regulator (CFTR) function and virulence factors acquired by the bacteria. Recently, neutrophil extracellular traps (NETs), extracellular structures composed of neutrophil chromatin complexed with granule contents, were identified as an alternative mechanism of pathogen killing. The hypothesis that NET-mediated killing of P. aeruginosa is impaired in the context of the CF airway was tested. P. aeruginosa induced NET formation by neutrophils from healthy donors in a bacterial density dependent fashion. When maintained in suspension through continuous rotation, P. aeruginosa became physically associated with NETs. Under these conditions, NETs were the predominant mechanism of killing, across a wide range of bacterial densities. Peripheral blood neutrophils isolated from CF patients demonstrated no impairment in NET formation or function against P. aeruginosa. However, isogenic clinical isolates of P. aeruginosa obtained from CF patients early and later in the course of infection demonstrated an acquired capacity to withstand NET-mediated killing in 8 of 9 isolates tested. This resistance correlated with development of the mucoid phenotype, but was not a direct result of the excess alginate production that is characteristic of mucoidy. Together, these results demonstrate that neutrophils can kill P. aeruginosa via NETs, and in vitro this response is most effective under non-stationary conditions with a low ratio of bacteria to neutrophils. NET-mediated killing is independent of CFTR function or bacterial opsonization. Failure of this response in the context of the CF airway may occur, in part, due to an acquired resistance against NET-mediated killing by CF strains of P. aeruginosa.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Anti-Bacterial Agents / pharmacology
  • Cell Adhesion / drug effects
  • Cell Separation
  • Cellular Structures / drug effects
  • Cellular Structures / metabolism*
  • Cystic Fibrosis / microbiology*
  • Cystic Fibrosis / pathology*
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism
  • Extracellular Space / drug effects
  • Extracellular Space / metabolism*
  • Humans
  • Lung / drug effects
  • Lung / microbiology
  • Lung / pathology
  • Microbial Sensitivity Tests
  • Microbial Viability* / drug effects
  • Neutrophils / cytology
  • Neutrophils / drug effects
  • Neutrophils / metabolism*
  • Pseudomonas aeruginosa / cytology*
  • Pseudomonas aeruginosa / drug effects
  • Pseudomonas aeruginosa / growth & development
  • Pseudomonas aeruginosa / isolation & purification
  • Suspensions

Substances

  • Anti-Bacterial Agents
  • Suspensions
  • Cystic Fibrosis Transmembrane Conductance Regulator