The high mortality rate amongst people with cystic fibrosis (CF) is associated with the incidence of lung disease. Pseudomonas aeruginosa is the most common pathogen isolated from the CF lung, and the environmental conditions drive adaptations leading to a chronic, biofilm infection that is highly resistant to antibiotics. Research is limited by the lack of a laboratory model that accurately recapitulates all aspects of human infection. This thesis has focused on development of an ex vivo pig lung (EVPL) model to further understand P. aeruginosa infection in the CF lung, using pig bronchiolar tissue and synthetic cystic fibrosis sputum media (SCFM).

Virulence factor assays demonstrated that P. aeruginosa virulence was at low levels in the EVPL model. Histological staining showed the P. aeruginosa biofilm on the surface of the tissue had an architecture comparable to patient biopsies, not observed in in vitro models. RNA-sequencing was then performed, and a distinction in P. aeruginosa gene expression in SCFM compared with the EVPL model was found. P. aeruginosa expression of quorum sensing genes was reduced in the EVPL biofilm, also observed in studies comparing CF sputum with in vitro growth. These findings demonstrated that the EVPL model facilitated a chronic-like P. aeruginosa infection. Investigation of the P. aeruginosa transcriptome over time in the EVPL biofilm provided further insight into infection dynamics and future optimisation for long term infection. Burkholderia cenocepacia and
Burkholderia multivorans were then introduced and it was shown that the EVPL model is also suitable for their growth, and to explore interactions during mixed infection with P. aeruginosa.

The EVPL model has been shown to capture key aspects of P. aeruginosa chronic biofilm infection in the CF lung. It can now be used to better understand these infections, and as a diagnostic and drug testing platform to improve treatment outcomes.