A33-53 Inter-kingdom Communication Between Klebsiella Pneumoniae And Alveolar Macrophages Facilitates Bacterial Pneumonia In Intubated Patients

Introduction

Colonization of the airways with Klebsiella pneumoniae in intubated patients often precedes ventilator-associated pneumonia (VAP).

Rationale

Colonization of the airways with Klebsiella pneumoniae (K. pneumoniae) in intubated patients is a risk factor for the development of ventilator-associated pneumonia (VAP). Interestingly, colonization with Stenotrophomonas maltophilia (S. maltophilia) rarely causes invasive infections in these patients. Yet, the mechanisms of this phenomenon are unclear. Alveolar macrophages (AMs) are the key sentinel leukocytes in the airways and are crucial to keep colonizing bacteria in check.

Objective

We set out to investigate the communication between bacterial extracellular vesicles and AMs, assuming that these diffusible signals might facilitate the development of VAP.

Methods

Bacterial extracellular vesicles of K. pneumoniae and S. maltophilia were isolated from bacterial cultures and respiratory samples of colonized patients. AMs were stimulated with bEVs, and their innate immune response to bacteria was analyzed. Mice were intratracheally stimulated with bEVs and consequently infected with bacteria. Bacterial extracellular vesicles were analyzed by proteomics. Knockout bacteria were generated by the CRISPR-Cas system.

Results

Bacterial EVs from K. pneumoniae, but not from S. maltophilia, diminish AMs’ capacity to clear bacteria, thereby enhancing bacterial outgrowth in an animal model. Mechanistically, OmpA, the most abundant protein in K. pneumoniae bEVs, prevents mitochondrial fission and thus the generation of bactericidal mitochondrial reactive oxygen species in response to bacteria. Colonized patients harbor large amounts of bEVs in their respiratory tract, recapitulating findings from in vitro bacterial cultures.

Conclusion

OmpA in bacterial EVs of K. pneumoniae but not S. maltophilia generated in vitro or isolated from colonized patients diminishes the capacity to clear bacteria by AMs, which enhances bacterial outgrowth in an experimental model in vivo. Thus, targeting OmpA might constitute a specific prophylactic approach to prevent VAP in colonized patients.

Colonization and risk of infection: PMID: 26867474

This abstract is funded by: German Research Foundation