16S rRNA Gene Sequencing Reveals Site-Specific Signatures Of The Upper And Lower Airways Of Cystic Fibrosis Patients

Abstract

RationaleChronic rhinosinusitis (CRS) is an inflammatory disorder of the sinonasal mucosa associated with microbial colonization. Metastasis of sinus microbiota into the lower airways is thought have significant implications in the development of chronic respiratory disease. However, this dynamic has not been thoroughly investigated in cystic fibrosis (CF) patients, where lower airway infections are the primary driver of patient mortality. Given the high prevalence of CRS in CF patients and the proposed infection dynamic between the upper and lower airways, a better understanding of sinus-lung continuum is warranted.\n\nObjectiveTo compare the microbiome of matched sinus mucus and lung sputum samples from CF subjects undergoing functional endoscopic sinus surgery (FESS) for treatment of CRS.\n\nMethodsMucus was isolated from the sinuses and lungs of twelve CF patients undergoing FESS. 16S ribosomal RNA gene sequencing was then performed to compare bacterial communities of the CF lung and sinus niches. Finally, functional profiling was performed to predict bacterial metagenomes from the 16S dataset, and was used to compare pathogenic bacterial phenotypes between the upper and lower airways.\n\nMeasurements and Main ResultsBacterial richness was comparable between airway sites, though sinus and lung environments differed in community evenness, with the sinuses harboring a higher prevalence of dominant microorganisms. Beta diversity metrics also revealed that samples clustered more consistently by airway niche rather than by individual. Finally, predicted metagenomes showed that anaerobic metabolism was enriched in the lung environment, while genes associated with both biofilm formation and Gram identity were not variable between sites.\n\nConclusionsSinus and lung microbiomes are distinct with respect to richness and evenness, while sinus communities have a higher incidence of a dominant taxon. Additionally, ordination analyses point to sinus and lung environments as being stronger determinants of microbial community structure than the individual patient. Finally, BugBase-predicted metagenomes revealed anaerobic phenotypes to be in higher abundance in the lung relative to the sinuses. Our findings indicate that while the paranasal sinuses and lungs may still comprise a unified airway in which lower airways are seeded by sinus microbiota, these discrete airway microenvironments harbor distinct bacterial communities.