Introduction: Chronic P. aeruginosa (PA) airway infections in patients with bronchiectasis (BE) are associated with increased disease severity and exacerbation frequency. PA biofilms are common and reduce the efficacy of antibiotics and immune-mediated clearance. Quorum sensing is regulated by systems including las, rhl and MexEF-OprN which impact biofilm formation and virulence gene expression.

Aims and objectives: To measure the genetic diversity of PA from BE patients with chronic infections and its impact on growth and biofilm formation.

Methods: Sputum PA clones were isolated from 100 BE patients with chronic PA infection across Europe and Australasia. Illumina sequencing identified genetic changes in genes compared to PAO1 (lasB, lasR, lasI, rhlR, mexF, mexE, oprN) or PA14 (mexT) reference strains. PA growth was measured at A_600nm for 24h. Biofilm formation was measured by crystal violet staining after 24h.

Results: 450 high/moderate impact variants were found in 93 clones across the genes studied. 7 clones had no variants in these genes. There was a growth defect in clones with variants in these genes (p=0.021, no variants=11.2±0.703A₆₀₀/h² [median±IQR], variants=9.07±2.73A₆₀₀/h²), linked to variants in lasR (p=0.028, WT lasR=10.2±3.28A₆₀₀/h², variants=8.77±2.00A₆₀₀/h²) or rhlR (p=0.020, WT rhlR=9.51±3.06A₆₀₀/h², variants=8.20±3.21A₆₀₀/h²). Biofilm formation increased in clones with lasB (p?0.001, WT lasB=0.258±0.250A₆₀₀, variants=0.655±0.627A₆₀₀) and oprN (p=0.044, WT oprN=0.288±0.571A₆₀₀, variants=0.566±0.504A₆₀₀) variants.

Conclusion: PA from BE infections have heterogenous genotypes, which influence growth and biofilm formation. If these variants affect virulence remains to be tested in vivo.