Microbial composition of induced sputum altered in mild asthma

The microbial composition of sputum in patients with mild asthma differs from that in individuals without the condition, results from a US study show.

Fernando Martinez (University of Arizona, Tucson) and team also found that patients with mild asthma had significantly greater bacterial diversity in their sputum than nonasthmatic individuals.

"Our results suggest that a disordered microbial composition of the respiratory tract… is not only present in patients with severe asthma but also in those with more mild disease, and could be a hallmark of asthma," they comment in the Journal of Allergy and Clinical Immunology.

The team studied sputum samples collected from 10 patients with mild, active asthma and 10 individuals without the condition; patients in both groups were younger than 28 years. Of those with asthma, most (80%) were not using inhaled corticosteroids and none reported using oral medications for asthma during the previous year.

The researchers note that all sputum samples contained Firmicutes, Proteobacteria, Actinobacteria, Fusobacterium, and Bacteroidetes, with the first three phyla accounting for more than 90% of the total sequences in both asthmatic and nonasthmatic participants.

However, sputum samples from patients with asthma had a significantly higher proportion of Proteobacteria than samples from nonasthmatic individuals, accounting for 37% versus 15% of the bacterial community.

By contrast, Firmicutes and Actinobacteria were present in higher proportions in samples from nonasthmatic individuals than in those from patients with asthma, at 63% versus 47% and 14% versus 10%, respectively. However, these differences were not significant.

Hierarchical clustering of bacterial composition produced two significant clusters, one that contained most of the samples from asthmatic patients (eight with asthma and one without asthma) and the second consisting predominantly of samples from nonasthmatic participants (two with asthma and seven without asthma).

"This further suggests the compositional similarity of samples associated with disease state," say the researchers.

Martinez et al conclude: "Young adults with mild asthma show changes in the composition of induced sputum microbiota compared with nonasthmatic subjects, and these changes might have implications for asthma pathogenesis and management."

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