Improvement in lung function following macrolide antibiotic therapy has been attributed to reduction in bronchial infection due to specific bacteria. However, the airway may be populated by a more diverse microbiota, and clinical features of asthma may be associated with characteristics of the airway microbiota present.
To determine if relationships exist between the composition of the airway bacterial microbiota and clinical features of asthma, using culture-independent tools capable of detecting the presence and relative abundance of most known bacteria.
In this pilot study, bronchial epithelial brushings were collected from sixty-five adults with sub-optimally controlled asthma participating in a multicenter study of the effects of clarithromycin on asthma control, and ten healthy subjects. A combination of high-density 16S rRNA microarray and parallel clone library-sequencing analysis was used to profile the microbiota and examine relationships with clinical measurements.
Compared to controls, 16S rRNA amplicon concentrations (a proxy for bacterial burden) and bacterial diversity were significantly higher among asthmatic patients. In multivariate analyses, airway microbiota composition and diversity were significantly correlated with bronchial hyperresponsiveness. Specifically, the relative abundance of particular phylotypes, including members of the Comamonadaceae, Sphingomonadaceae, Oxalobacteraceae and other bacterial families, were highly correlated with the degree of bronchial hyperresponsiveness.
The composition of bronchial airway microbiota is associated with the degree of bronchial hyperresponsiveness among patients with sub-optimally controlled asthma. These findings support the need for further functional studies to examine the potential contribution of members of the airway microbiota in asthma pathogenesis.