Pseudomonas aeruginosa gene expression changes during established biofilm infection in a cystic fibrosis lung model; Niamh E. Harrington, Freya Allen, Ramón Garcia Maset & Freya Harrison

Supplementary Material for ‘Pseudomonas aeruginosa gene expression changes during established biofilm infection in a cystic fibrosis lung model’, as described in Microbiology. The opportunistic pathogen Pseudomonas aeruginosa forms biofilm infections in the lungs of people with the genetic condition cystic fibrosis (CF) that can persist for decades. There are numerous P. aeruginosa lifestyle changes associated with chronic biofilm infection cued by the CF lung environment. These include a loss of virulence, metabolic changes and increased antimicrobial tolerance. We have investigated P. aeruginosa PA14 biofilm infection over 7 d in an ex vivo pig lung (EVPL) model for CF, previously shown to facilitate formation of a clinically relevant P. aeruginosa biofilm structure with expression of key genes comparable to human infection. We have compared P. aeruginosa gene expression between sequential time points: 24 h, 48 h and 7 d post infection, and investigated tolerance to polymyxins. Our results demonstrate that the EVPL model can maintain a P. aeruginosa biofilm population, which exhibits increased antibiotic tolerance, for at least 7 d. Differential expression of antimicrobial resistance-associated genes was not observed, however there was significant upregulation of sulfur metabolism and maintenance of a structured biofilm. Our findings demonstrate that 7 d is a viable time point for studying established, chronic biofilm infection in the EVPL model, and provide insight into the accompanying gene expression changes.