Investigation of pure lung microbiota in patients with lung cancer after eliminating upper airway contamination: a prospective cohort study

Background: While the relationship between gut microbiota and gastrointestinal cancer has been elucidated, the relationship between lung microbiota and lung cancer remains unclear. Previous study findings are inconclusive due to the possibility of contamination by upper airway microbiota in samples obtained from the oropharynx, such as saliva and sputum, and bronchoalveolar lavage fluid (BALF) collected during bronchoscopy. Therefore, this study aimed to detect pure lung microbiota in patients with lung cancer using BALF samples from resected lung specimens. Additionally, we aimed to evaluate the lung microbiota to clarify their relationship with lung cancer and aid in postoperative pneumonia (POP) prevention and treatment.

Methods: This prospective cohort study enrolled patients with clinically suspected lung cancer who underwent surgical resection at the Department of Thoracic Surgery, Japanese Red Cross Suwa Hospital, between April 2020 and March 2022. BALF from resected lung specimens collected under sterile conditions were used for high-throughput next-generation sequencing (NGS) and bacterial culture analyses. Pure lung microbiota were identified, and their abundance ratio was analyzed. Additionally, we performed α-diversity analysis and explored the relationship between microbiota and POP by comparing our findings with previous literature.

Results: Among samples collected from 54 included cases, bacteria were detected in 13 samples (24.1%) via bacterial culture and in all samples via NGS. Candidate Phylum OD1 bacteria (OD1) was present in a large proportion of samples (phylum level). The major bacteria genera, with a relative abundance ratio (each bacterial read amount/total bacterial read amount) >1% in at least one sample, included Aquabacterium, Acinetobacter, and Ralstonia. Additionally, bacteria widely recognized as pathogens of POP were detected.

Conclusions: Our lung microbiota sampling method eliminated contamination from upper airway microbiota, allowing detection of pure lung microbiota. This study provides baseline data on pure lung microbiota and highlights the need for further research to explore the role of OD1 in lung cancer, which was previously unreported in lung microbiota. Although the pathogens of POP can be aspirated post-hospitalization, they could already exist as lung microbiota pre-hospitalization. Further investigation is needed to substantiate our results and hypothesis.