Reemergence of Lower-Airway Microbiota in Lung Transplant Patients with Cystic Fibrosis.

Rationale: Chronic lung infections are a hallmark of cystic fibrosis; they are responsible for progressive airway destruction and ultimately lead to respiratory death or the requirement for life-saving bilateral lung transplant. Furthermore, recurrent isolation of airway pathogens such as Pseudomonas aeruginosa in the allograft after transplant is associated with adverse outcomes, including bronchiolitis obliterans syndrome and acute infections. Little information exists on the impact of bilateral lung transplant on the lower-airway microbiota.

Objectives: To compare, at a microbiome and single-pathogen level (P. aeruginosa), the bacterial communities in pre- and post-transplant samples.

Methods: We retrospectively accessed our biobank of sputum samples and sputum-derived bacterial pathogens for patients who had matched samples, including those who were clinically stable before transplant, those who had a pulmonary exacerbation before transplant, and those who had pulmonary exacerbation after transplant. We used 16S ribosomal RNA gene sequencing to characterize the lower-airway microbiome of 14 adult transplant patients with cystic fibrosis. Genotyping and phenotyping of P. aeruginosa isolates from 12 of these patients with matched isolates was performed.

Measurements And Main Results: Although α-diversity (richness and evenness) of patient microbiomes was similar before and after transplant, β- diversity (core microbiome composition) measures stratified patients evenly into two groups with more similar and more dissimilar communities. P. aeruginosa strains isolated before transplant were found to reemerge in 11 of 12 patients; however, phenotypic variation was observed.

Conclusions: These findings indicate that recolonization by P. aeruginosa after transplant is almost always strain specific, suggesting a within-host source. The polymicrobial colonization of the airways after transplant does not always reflect the pretransplant sputum microbiota.