This study explored the relationship between total bacterial density, airway microbiota composition and clinical parameters in bronchiectasis. We determined changes with time during clinical stability and following antibiotic treatment of a pulmonary exacerbation.

We conducted a multicentre longitudinal cohort study of UK participants with CT confirmed bronchiectasis. Sputum samples and clinical parameters [FEV₁% predicted, lung clearance index, C-reactive protein, white cell count and Quality of Life] were collected when participants were clinically stable and pre/post-antibiotic treatment of an exacerbation. Total bacterial density and microbiota community composition was measured by quantitative polymerase chain reaction and sequencing of the V4 region of bacterial 16S rRNA, respectively.

Among 105 participants at baseline, 65 (62 %) were female with a mean age of 65 years and FEV₁ at 69 % predicted. In participants who remained clinically stable (n = 15), no significant changes were observed in bacterial density, microbiota diversity, richness, evenness, and dominance (p = 0.30, 0.45, 0.54, 0.23 and 0.43; respectively) across four time points over a 1-year period. Similarly, for participants with paired pre/post-antibiotic treatment samples (n = 19), no significant changes were observed (p = 0.30, 0.46, 0.44, 0.71 and 0.58; respectively). However, considerable fluctuation in community composition between samples was apparent for most patients. Total bacterial density and microbiota composition did not correlate with clinical parameters at baseline (n = 75).

Stability in bacterial density and microbiota diversity, richness, evenness and dominance was observed over time at a population level but considerable fluctuation was apparent in samples from individual patients.