Disordered microbial communities in asthmatic airways

Abstract

Background: A rich microbial environment in infancy protects against asthma [1], [2] and infections precipitate asthma exacerbations [3]. We compared the airway microbiota at three levels in adult patients with asthma, the related condition of COPD, and controls. We also studied bronchial lavage from asthmatic children and controls.

Principal findings: We identified 5,054 16S rRNA bacterial sequences from 43 subjects, detecting >70% of species present. The bronchial tree was not sterile, and contained a mean of 2,000 bacterial genomes per cm(2) surface sampled. Pathogenic Proteobacteria, particularly Haemophilus spp., were much more frequent in bronchi of adult asthmatics or patients with COPD than controls. We found similar highly significant increases in Proteobacteria in asthmatic children. Conversely, Bacteroidetes, particularly Prevotella spp., were more frequent in controls than adult or child asthmatics or COPD patients.

Significance: The results show the bronchial tree to contain a characteristic microbiota, and suggest that this microbiota is disturbed in asthmatic airways.

Figure 1. Phylogenetic analysis of bacterial 16S rRNA DNA from the nose, oropharynx (OP) and left upper lobe (LUL) in adult patients with COPD (C) or asthma (A) and healthy controls (N).

The numbers of 16S rRNA gene phylotypes (OTUs) were calculated at 97% sequence identity and single-sequence OTUs omitted. OTU designations are located at the termination of each branch and represent potential organism names. Abundance of OTUs in each subject is indicated by different coloured squares (Yellow = 1 single OTU, Orange = 3–10%, Red = 10–20% and Black≥20%).

Figure 2. Percentage distribution of common phyla and genera at different airway levels (nose, OP and LUL), subdivided into the seven most frequent genera (Croynebacterium, Prevotella, Staphylococcus, Streptococcus, Veilonella, Haemophilus and Neisseria) found in the samples.

Figure 3. Bacterial community comparisons from the nose (N), oropharynx (OP) and left upper lobe (LUL) in adult patients with COPD or asthma and healthy controls.

Figure 4. Distribution of common phyla and genera in diseased and normal bronchi.

a) Distribution of the phyla from sheathed bronchoscopic brushings of the LUL for patients with asthma and COPD and normal subjects, subdivided into the seven most frequent genera (Croynebacterium, Prevotella, Staphylococcus, Streptococcus, Veilonella, Haemophilus and Neisseria). b) Distribution of the phyla from bronhco-alveolar lavage (BAL) in children with difficult asthma and controls.