Microbiome characteristics of induced sputum compared to bronchial fluid and upper airway samples

The study of the community of microorganisms (the microbiota) in the lower airways in children is restricted to opportunistic sampling in children undergoing elective general anaesthetic. Here we tested the hypothesis that induced sputum is a valid alternative to directly sampling the lower airways to study lower airway microbiota.

Children scheduled for elective operations were recruited. Pre-operatively a sample of induced sputum was obtained. After anaesthesia was induced, a bronchial brushing and swabs of the upper respiratory tract were obtained. Bacterial community analysis was performed by amplification of the V3-V4 16S rRNA gene region.

Twenty children were recruited, mean age 10.7 years. Induced sputum samples were obtained from 12 children, bronchial brushing from 14 and nasal, mouth, and throat samples in 15, 16, and 17 children. The profile of bacterial communities was similar in the mouth, throat, and sputum samples with the nose and bronchial samples being different. Actinobacteria species dominated the nose and mouth, Fusobacteria were the dominant species in the throat and sputum while Proteobacteria species dominated in bronchial samples. Forty-one percent of detected bacteria in bronchial samples were unclassified. Bacterial communities from the mouth, throat, and induced sputum were tightly clustered and were distinct from nose and those found in bronchial communities.

Induced sputum may not be a valid surrogate for microbiome assessment of the lower airways in all individuals. Many bacteria in bronchial samples were not recognized by standard testing, suggesting that our understanding of the lower airway microbiota in children remains rudimentary.