Pseudomonas aeruginosa transcriptome analysis in a cystic fibrosis lung model reveals metabolic changes accompanying biofilm maturation and increased antibiotic tolerance over time.

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 provide further insight into the increased P. aeruginosa antibiotic tolerance during chronic infection of the CF lung, and suggest we can cue aspects of chronic infection in 7 d under the right lab conditions.