Disease-associated changes in the lung microbiome in patients with early chronic obstructive pulmonary disease

Chronic obstructive pulmonary disease (COPD) is associated with airway inflammation and microbiota dysbiosis. However, the function of lung microbiome alteration in early COPD remains unclear. This study is the first to characterize the lower respiratory tract microbiota in early COPD patients via bronchoalveolar lavage fluid (BALF) samples. By using full-length 16S sequencing, we found that the lung microbiome of early COPD patients had lower bacterial richness and significant compositional differences than did that of the healthy smoker controls. Streptococcus was the most robustly distinguished genus in early COPD patients and was associated with decreased lung function and increased host local inflammation. Furthermore, a murine cigarette smoke model of early COPD revealed that Streptococcus mitis promotes the progression of early COPD. Single-cell transcriptomics revealed that Streptococcus mitis increased emphysematous destruction of the lung parenchyma in a mouse early COPD model by regulating the function of alveolar type II (AT2) cells and macrophages. Therefore, targeting the lower airway microbiota in combination with smoking cessation may be a potential therapeutic approach for early COPD. We established a cigarette smoke-induced murine COPD model and investigated the role of Streptococcus mitis by intratracheally inoculating mice with S.mitis every 3 days for 4 weeks, followed by exposure to smoke for 12 weeks; single-cell RNA sequencing was then performed on lung samples from control, smoke-exposed, and smoke-exposed S.mitis-colonized mice