Defining the baseline of pulmonary microbiota in healthy populations and influencing factors

Abstract

Lung microbiota and lung diseases have already received increasing attention. However, the lung microbiota lacks a unified healthy baseline. In this review, we collect the healthy pulmonary microbial composition based on the data of existing relevant studies. Subsequently, we discuss and analyze the three aspects of bacterial, fungus and viral at the phylum and genus levels, as well as influence factors like sample type, geography, age, time, hypervariable regions and sequencing method to set up a unified pulmonary baseline. We conclude that Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria and Fusobacteria are the predominant phyla in healthy people. At the genus level, the most common bacterial genera are Veillonella, Streptococcus, Prevotella, Neisseria and Fusobacterium. A significant difference exists at the bacterial genus level between the lung of healthy subjects and the normal tissues of patients, and geography impacts on the healthy baseline significantly. In addition, age, time, hypervariable regions and sequencing method all affect the baseline to various degrees. In healthy people, Ascomycota and Basidiomycota dominate the pulmonary fungal phyla, while bacteriophages are the predominated order in virome. Our investigation provides a healthy lung baseline for the study of lung microbiota, which is conducive to better finding lung disease-related pathogens.