Pseudomonas aeruginosa gene expression changes during established biofilm infection in a cystic fibrosis lung model

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