Microbiological profiles in sputum and in regions of airway damage

Project Leader:

Alix Ashare, M.D., Ph.D.
Assistant Professor of Medicine Geisel School of Medicine at Dartmouth


Deborah A. Hogan, Ph.D.
Associate Professor, Microbiology and Immunology Geisel School of Medicine at Dartmouth

Drs. Hogan and Ashare are working together on several projects with a long-term goal of identifying strategies that prevent or arrest the progressive loss of lung function that plagues individuals with cystic fibrosis (CF). Lung function decline in CF can be largely attributed to irreversible destruction of the muscle and elastic tissue of the airways, a process referred to as bronchiectasis. Bronchiectasis develops in localized regions of the lung, and these specific regions of bronchiectasis worsen over time. Bronchiectasis in CF has been linked to both microbial species composition and virulence phenotypes. For example, detection of mucoid P. aeruginosa in CF sputum is associated with markedly accelerated bronchiectatic progression and reduction in FEV1. Other microbes have also been associated with more rapid lung function decline. While initial studies of chronic CF and non-CF lung infections suggest that there is spatial heterogeneity in the lung microbiota, the relationships between the local microbiota and proximal bronchiectatic damage in CF are not known. Our overarching hypothesis states that we must understand the microbiological profiles specifically in regions of lung damage in order to identify which microbial species or phenotypes most strongly correlate with onset or early progression of bronchiectasis, and thus represent the most promising therapeutic targets. The specific aims of this project are to: 1) quantify differences in diversity and species composition of the active microbiota in regions of the lung with more and less severe disease; 2) determine if sputum microbiology is representative of areas of more severe lung disease; and 3) investigate whether levels of P. aeruginosa transcripts associated with mucoidy and other virulence factors are higher in regions of more severe lung disease. In addition, because sputum is very often analyzed to gain insight into the microbes in the lung for the purposes of research and to guide clinical care, we are comparing the microbial composition in sputum to that in different regions of the lung to test the hypothesis that sputum reveals microbiological parameters in the regions of the lung with damage.

To address these important questions, we are analyzing sputum and bronchoalveolar lavage samples from different regions of the lungs of CF subjects to correlate microbiological parameters with the extent of regional damage as assessed by computed tomography (CT) scans. Our studies will 1) identify or validate which therapeutic targets most strongly correlate with the onset or progression of irreversible lung damage including specific bacterial or fungal species and specific P. aeruginosa strains, 2) determine if alginate production, in either mucoid or non-mucoid strains, is elevated in regions of more severe damage, 3) monitor the regional expression of numerous P. aeruginosa virulence-related transcripts that are relevant to research in the Dartmouth Lung Biology Center to guide future research avenues and to support future grant applications, and 4) learn how sputum microbiology reflects aspects of airway microbiology that is most relevant to CF lung disease.