Mucoid Pseudomonas aeruginosa alters sputum viscoelasticity in patients with non-cystic fibrosis bronchiectasis

Abstract

Introduction and aim: Pseudomonas aeruginosa could acquire a mucoid phenotype due to mutations in mucA (mucoid Pseudomonas aeruginosa - mPA) that is a hallmark of poor prognosis in patients with bronchiectasis. Despite the higher prevalence of Pseudomonas aeruginosa in bronchiectasis, how mPA and non-mucoid Pseudomonas aeruginosa (non-mPA) phenotypes could affect viscoelastic properties of sputum is unknown. Our aim was to determine the relationship between Pseudomonas aeruginosa phenotypes isolation, the viscoelastic properties of sputum and the clinical outcomes in patients with bronchiectasis.

Methods: A cross-sectional study was conducted of sputum samples obtained by spontaneous expectoration and sent for microbiology and rheology analysis. Elasticity and viscosity were measured at two oscillatory frequencies (1 and 100 rad/s). Socio-demographic and clinical data were recorded.

Results: We analyzed 17 patients with mPA, 14 with non-mPA and 17 with no organism reported (NOR). Compared with the NOR group, the mPA group showed higher elasticity (median 10.30 vs. 5.70, p = 0.023), viscosity (2.40 vs. 1.50, p = 0.039), and stiffness (10.70 vs. 6.00, p = 0.024). Values in the mPA group tended to be higher compared with non-mPA. Clinically, the mPA group showed greater hospitalizations during the previous year and greater affected lobes than the non-mPA and NOR groups.

Conclusions: The mPA phenotype is associated with increased elasticity, viscosity and stiffness of bronchiectatic sputum. Viscoelastic properties could be used as a marker of poor mucociliary clearance in mPA, with potentially important clinical implications.

Keywords: Bronchiectasis; Mucoid Pseudomonas aeruginosa; Rheology; Sputum; Viscoelastic properties.