Proteobacteria community compositions correlate with bronchiectasis severity

BACKGROUND: Proteobacteria contributes to airway inflammation and poor clinical outcomes in bronchiectasis. OBJECTIVE : To compare sputum Proteobacteria compositions according to bronchiectasis severity. METHODS : Sputum samples collected from 106 patients with stable bronchiectasis and 17 healthy subjects were split for 16srRNA sequencing and biomarker measurement. Pairwise changes in Proteobacteria compositions among 22 of 106 patients during stability, exacerbations and convalescence were compared. Patients were stratified based on the Bronchiectasis Severity Index (BSI). RESULTS : Respectively 44, 34 and 28 patients had mild, moderate and severe bronchiectasis. A higher BSI was associated with a greater relative abundance of Proteobacteria and lower Shannon-Wiener diversity index, Simpson diversity index and bacterial richness. Similar findings applied at genera levels. Proteobacteria and Pseudomonas were the major phylum and genus, respectively, contributing to community similarity in moderate-to-severe bronchiectasis. These significant correlations were not observed in those in whom Pseudomonas aeruginosa was not isolated. Proteobacteria abundance correlated with lung function, but not sputum inflammatory biomarkers in severe bronchiectasis. Proteobacteria compositions in severe bronchiectasis were less likely to change significantly during exacerbations and convalescence. CONCLUSION: Proteobacteria compositions (particularly culturable Pseudomonas abundance) were correlated with bronchiectasis severity. Proteobacteria and Pseudomonas contributed most to community similarity in patients with a higher BSI, indicating microbial targets for interventions in severe bronchiectasis.