Towards a clinically relevant model for investigation of host-microbe interactions in ventilator-associated pneumonia

Ventilator-associated pneumonia (VAP) is amongst the most common healthcare-associated infections worldwide. Current understanding of the underlying mechanisms has focussed on either the microbiological or physiological elements but host-microbe interactions, which are instrumental in pathogenesis, have received less research focus. This work aims to explore clinically relevant and reproducible models to investigate these interactions in the context of VAP. A clinical isolate of Pseudomonas aeruginosa, a pathogen common in VAP, was investigated in systems of increasing complexity. Sensitivity to key antibiotics (LVX, MEM, and TZP) used for treatment of VAP was unaffected by the presence of cytokines (IL-1β, IL-6, and TNFα) in vitro. Larvae of Galleria mellonella, an in vivo insect model with a rudimentary immune system, was used to test virulence of P. aeruginosa, Staphylococcus aureus and Klebsiella pneumoniae. P. aeruginosa killed 100 % of larvae within 24 h. S. aureus and K. pneumoniae killed 43.5 % and 50 % of larvae respectively, within 8 days. An ex vivo mammalian model was developed, which demonstrated abundant P. aeruginosa proliferation on lung tissue. After validating inactivation of host lung tissue, we identified changes in the expression of P. aeruginosa quorum sensing genes LasI and RhlI, specifically induced by host interaction. Our results suggest that host factors may influence bacterial growth and gene expression. We will use these early data to validate and expand our models prior to investigation of clinical samples from VAP patients. We will report our most recent findings in the development of clinically relevant models to investigate VAP.