Genetic diversity of Pseudomonas aeruginosa virulence factors in bronchiectasis

<b>Introduction:</b> Chronic <i>P. aeruginosa</i> (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 <i>las</i>, <i>rhl</i> and MexEF-OprN which impact biofilm formation and virulence gene expression. <b>Aims and objectives:</b> To measure the genetic diversity of PA from BE patients with chronic infections and its impact on growth and biofilm formation. <b>Methods:</b> 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 (<i>lasB</i>,<i>lasR</i>, <i>slasI</i>, <i>rhlR</i>, <i>mexF</i>, <i>mexE</i>, <i>oprN</i>) or PA14 (<i>mexT</i>) reference strains. PA growth was measured at A_600nm for 24h. Biofilm formation was measured by crystal violet staining after 24h. <b>Results:</b> 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 <i>lasR</i> (p=0.028, WT <i>lasR</i>=10.2±3.28A₆₀₀/h², variants=8.77±2.00A₆₀₀/h²) or <i>rhlR</i> (p=0.020, WT <i>rhlR</i>=9.51±3.06A₆₀₀/h², variants=8.20±3.21A₆₀₀/h²). Biofilm formation increased in clones with <i>lasB</i> (p≤0.001, WT <i>lasB</i>=0.258±0.250A₆₀₀, variants=0.655±0.627A₆₀₀) and <i>oprN</i> (p=0.044, WT oprN=0.288±0.571A₆₀₀, variants=0.566±0.504A₆₀₀) variants. <b>Conclusion:</b> PA from BE infections have heterogenous genotypes, which influence growth and biofilm formation. If these variants affect virulence remains to be tested in vivo.