Macrophages, but not neutrophils, are critical for proliferation of Burkholderia cenocepacia and ensuing host-damaging inflammation

PLoS Pathog. 2017 Jun 26;13(6):e1006437. doi: 10.1371/journal.ppat.1006437. eCollection 2017 Jun.


Bacteria of the Burkholderia cepacia complex (Bcc) can cause devastating pulmonary infections in cystic fibrosis (CF) patients, yet the precise mechanisms underlying inflammation, recurrent exacerbations and transition from chronic stages to acute infection and septicemia are not known. Bcc bacteria are generally believed to have a predominant extracellular biofilm life style in infected CF lungs, similar to Pseudomonas aeruginosa, but this has been challenged by clinical observations which show Bcc bacteria predominantly in macrophages. More recently, Bcc bacteria have emerged in nosocomial infections of patients hospitalized for reasons unrelated to CF. Research has abundantly shown that Bcc bacteria can survive and replicate in mammalian cells in vitro, yet the importance of an intracellular life style during infection in humans is unknown. Here we studied the contribution of innate immune cell types to fatal pro-inflammatory infection caused by B. cenocepacia using zebrafish larvae. In strong contrast to the usual protective role for macrophages against microbes, our results show that these phagocytes significantly worsen disease outcome. We provide new insight that macrophages are critical for multiplication of B. cenocepacia in the host and for development of a fatal, pro-inflammatory response that partially depends on Il1-signalling. In contrast, neutrophils did not significantly contribute to disease outcome. In subcutaneous infections that are dominated by neutrophil-driven phagocytosis, the absence of a functional NADPH oxidase complex resulted in a small but measurably higher increase in bacterial growth suggesting the oxidative burst helps limit bacterial multiplication; however, neutrophils were unable to clear the bacteria. We suggest that paradigm-changing approaches are needed for development of novel antimicrobials to efficiently disarm intracellular bacteria of this group of highly persistent, opportunistic pathogens.

MeSH terms

  • Animals
  • Burkholderia Infections / immunology
  • Burkholderia cenocepacia / isolation & purification*
  • Burkholderia cepacia complex / immunology
  • Cross Infection / microbiology*
  • Cystic Fibrosis / complications
  • Humans
  • Inflammation / microbiology*
  • Lung / microbiology
  • Macrophages / microbiology*
  • Neutrophils / immunology
  • Neutrophils / microbiology*
  • Phagocytosis / immunology
  • Pseudomonas aeruginosa / physiology
  • Respiratory Tract Infections / microbiology

Grant support

This study was supported by l'Institut National de la Santé et de la Recherche Médicale INSERM and Université de Montpellier. ACV was recipient of a ‘Chercheur d’avenir’ award from La Région Languedoc Roussillion, and JM from a doctoral grant from the French Ministry of Higher Education and Research and a ”Bourse de stage d’Excellence "Eole" du Réseau franco-néerlandais”. MBG was supported by “Vaincre la Mucoviscidose”. JRF was recipient of a doctoral grant from Fundação Ciência e Tecnologia (FCT), Portugal. MV and AHM were supported by the Smart Mix Program of the Netherlands Ministry of Economic Affairs and the Ministry of Education (SSM06010), Culture and Science. Work in the groups of ACV and AHM was also supported by the Marie-Curie Initial Training Network FishForPharma (PITN-GA-2011-289209). LZ was Marie-Curie fellow in the FishForPharma network. MCG was recipient of the French Ministry of Higher Education and Research. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.