The association between the respiratory tract microbiome and clinical outcomes in patients with COPD

Though it has been widely accepted that infections of the respiratory tract is associated with aetiology of acute exacerbation of chronic obstructive pulmonary disease (AECOPD), more recent techniques have shown emerging evidence on the importance of alterations of diversity and composition of microbiota itself in the disease process. Specifically, these alterations is widely present in COPD patients from a variety of populations, and is associated with severity of disease, frequency of acute exacerbation, as well as prediction of exacerbation. In addition, the microbiota from respiratory tract contributes to disease mechanisms, and more recently have been shown to interact with gut microbiota in a bidirectional way. Therefore, updating progress in the field is crucial as it not only reveals potential underlying mechanisms of the disease, but also highlights the potential utilisation of microbiota as a biomarker for disease prediction and as a target for treatment. In this narrative review, we summarize current updates on microbiota dysbiosis in COPD, including techniques for sampling and analysis of microbiota, recent findings on the presence of microbiota dysbiosis and its correlation with clinical prediction and prognosis of the disease, as well as its potential roles in disease mechanisms. In addition, how gut-lung axis contributes to COPD progression is also discussed. Finally, we addressed the utilisation of prebiotic and probiotic treatment for COPD. Together, we hope to provide useful information to advocate the use of microbial parameters as important tools for diagnosis, treatment and long-term follow-up for COPD patients.