The airway microbiome in COPD, bronchiectasis and bronchiectasis-COPD overlap.

Objective: To review the airway microbiome in chronic obstructive pulmonary disease (COPD), bronchiectasis and bronchiectasis-COPD overlap (BCO).

Data Source And Study Selection: Relevant studies were selected from PubMed, Google scholar, EMBASE and Web of Science. All studies involving human microbiomes, published in the English language, and using the search terms "COPD", "Chronic Obstructive Pulmonary Disease", "Bronchiectasis", "BCO" or "Bronchiectasis and COPD overlap", AND "microbiome", "mycobiome" or "metagenomics" were included.

Results: Despite variability in sampling methods and specimen types used, microbiome composition remains relatively comparable in COPD and bronchiectasis with prominence of Proteobacteria, Firmicutes and Bacteroidetes. Alterations to airway microbiomes occur in association to disease severity and/or exacerbations in COPD and bronchiectasis. Decreased alpha diversity and Haemophilus-predominant microbiomes are associated with poorer survival in COPD, while, in bronchiectasis, Pseudomonas-predominant microbiomes demonstrate high exacerbation frequency and greater symptom burden while Aspergillus-dominant mycobiome profiles associate with exacerbations. The role of the microbiome in BCO remains understudied.

Conclusion: Use of next-generation sequencing has revolutionised our detection and understanding of the airway microbiome in chronic respiratory diseases such as COPD and bronchiectasis. Targeted amplicon sequencing reveals important associations between the respiratory microbiome and disease outcome while metagenomics may elucidate functional pathways. How best to apply this information into patient care, monitoring and treatment, however, remains challenging and necessitates further study.