Molecular study of the lung microbiome in patients with non-cystic fibrosis bronchiectasis: the contribution of Pseudomonas aeruginosa infection to clinical outcomes

Introduction: Bronchiectasis is a chronic disease characterized by a pathologic dilation of the bronchi and bronchioles, due to a repetitive cycle of inflammation followed by infections causing structural damage and recurrent exacerbations. Pseudomonas aeruginosa is the most common bacteria detected in bronchiectasis in Southern Europe and could acquire a mucoid phenotype due to mutations in mucA (mucoid Pseudomonas aeruginosa - mPA) that is a hallmark of poor prognosis. Despite the higher prevalence of Pseudomonas aeruginosa in bronchiectasis, how mPA phenotype could affect viscoelastic properties of sputum is unknown. Bronchiectasis exacerbations are often treated with prolonged antibiotic use, even though there is limited evidence for this approach. More severe and frequent exacerbations are associated with worse quality of life and respiratory function, more hospital admissions, higher mortality, and increased economic burden. Aims: Our aims were: 1) to determine the relationship between Pseudomonas aeruginosa phenotypes isolation, the viscoelastic properties of sputum and the clinical outcomes in patients with bronchiectasis; 2) to investigate the baseline clinical and microbiological findings associated with long courses of antibiotic treatment in exacerbated bronchiectasis patients; 3) to evaluate patient characteristics during an exacerbation requiring hospital admission associated with mortality during a one-year period. Methods: A cross-sectional first 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). Furthermore, we conducted a second bi-centric prospective observational study of bronchiectasis exacerbated adults. We compared groups receiving short (<14 days) and long (15–21 days) courses of antibiotic treatment. Previous medical history, radiological features, symptoms, and laboratory and microbiological were recorded. 3 Finally, all patients were re-examined one year after hospital discharge to assess mortality. Results: Firstly, 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. Secondly, we enrolled 191 patients (mean age 72 (63, 79) years; 108 (56.5%) females), of whom 132 (69%) and 59 (31%) received short and long courses of antibiotics, respectively. Multivariable logistic regression of the baseline variables showed that long-term oxygen therapy (LTOT), moderate–severe exacerbations, and microbiological isolation of Pseudomonas aeruginosa were associated with long courses of antibiotic therapy. When we excluded patients with a diagnosis of community-acquired pneumonia (n = 49), in the model we found that an etiology of Pseudomonas aeruginosa remained as factor associated with longer antibiotic treatment, with a moderate and a severe FACED score and the presence of arrhythmia as comorbidity at baseline. Thirdly, we followed up 185 exacerbated bronchiectasis patients admitted to hospital (94 females, 71.8 (11.8) years, 66.5% BSI stage severe) for one-year. Twenty-three (12.4%) patients died during the one-year follow up. The major causes of death were respiratory related (68%), cardiovascular (18%), and septic shock (14%). LTOT, mechanical ventilation and white blood cell count at day 1 of hospitalization >13.64x 109/L are variables associated with an increased risk of one-year mortality in patients hospitalized with moderate or severe bronchiectasis exacerbation. On the other hand, influenza vaccination appears as a protective factor. 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. 4 Decisions about the duration of antibiotic therapy should be guided by clinical and microbiological assessments of patients with infective exacerbations. A future study addressing the risk of one-year mortality after a hospitalization for moderate to severe bronchiectasis exacerbation is desirable.