Features of the Bronchial Bacterial Microbiome Associated with Allergy and Mild Allergic Asthma.

Rationale: While the composition of lower airway microbiota has been reported to differ in subjects with asthma compared to healthy controls, it is unclear whether these differences are a function of asthma or are related to allergy. Here we dissect the specific bacterial taxa associated with mild allergic asthma and those associated with allergy alone, in an attempt to identify potential bacterial contributors to asthma pathogenesis.

Methods: Bacterial composition in protected bronchial brushings, from 28 mild corticosteroid-naïve allergic asthmatics (AA), 15 allergic non-asthmatics (AN) and 13 non-allergic non-asthmatics healthy controls (HC), was profiled using 16S rRNA sequencing on the Illumina MiSeq platform.

Results: Compared to AN and HC, AA exhibited a loss of bacterial taxa, such as Lactobacillus, and Methylobacterium, which were predicted to encode putatively protective functions, and increased relative abundance of Haemophilus, Neisseria, Porphyromonas and Sphingomonodaceae. A number of these taxa were significantly correlated with systemic eosinophilia and elevated serum IgE, implicating these organisms as potential contributors of eosinophilic inflammation in allergic asthma. A number of taxa, including Fusobacterium, Actinomyces and Treponema, which were enriched in AA compared to HC airways were also enriched in AN compared to HC, and were considered as allergy-associated.

Conclusions: This study distinguishes taxa associated with allergy from those which are potential contributors to asthma pathogenesis.  Understanding which specific members of the airway microbial community associated with allergy and which are associated with asthma may prove crucial for development of targeted therapeutics to control, or ideally, to prevent the development of disease.