Pseudomonas aeruginosa infection exacerbates elastase induced lung damage: Characterisation of a novel murine two-hit model of pulmonary infection

Background Pulmonary bacterial infections remain a hallmark of a range of respiratory diseases including Cystic Fibrosis (CF), Chronic Obstructive Pulmonary Disease (COPD) and non-CF bronchiectasis (NCFBE). Chronic persistent infections in the lung including P. aeruginosa are characterised by periods of stability punctuated by acute pulmonary exacerbations (PExs). Whilst animal infection models can reliably replicate acute and stable chronic infections, none currently replicate appropriate ‘acute-on-chronic’ pathophysiological backgrounds required to model PExs. Here, we aimed to establish a novel two-hit model of chronic P. aeruginosa infection where animals were first subjected to elastase challenge inducing pulmonary inflammation and injury reflective of the CF/COPD lung and subsequently infected with P. aeruginosa , utilised for its commonality across PExs in CF, COPD and NCFBE patients. Methods Mice were challenged with 2mg/kg Porcine Pancreatic Elastase (PPE) on days 1, 4 and 7 before infection with 1x10 ⁶ cfu/mouse P. aeruginosa strain RP73, 3 days post final PPE challenge. 2-, 5-, and 7- days post infection, both pulmonary microbiological and inflammatory readouts were quantified. Results PPE induced significant pulmonary neutrophil recruitment alongside structural markers of lung injury characteristic of CF, COPD and NCFBE. In the two-hit cohort, bacterial clearance following P. aeruginosa infection was significantly impaired in animals first subjected to repeated elastase challenge. This was accompanied by exacerbated neutrophilic recruitment and activation, accelerating PPE induced lung damage characteristic of PExs. Conclusions Taken together, this two-hit model of pulmonary infection with P. aeruginosa following PPE induced lung injury replicates key pathophysiological changes consistent with PExs relevant to CF, COPD and NCFBE patients.