Methods: Induced sputum samples were obtained from 49 non-smoking patients with stable asthma and 15 healthy subjects. Total DNA was amplified by using primers specific for the V3-V5 hypervariable region of bacterial 16s rRNA. Samples were barcoded, and sequenced with the 454 GS FLX sequencer. Sequences were assigned to bacterial taxa by comparing them with 16s rRNA sequences in the Ribosomal Database Project.
Results: Asthmatics had lower FEV1% predicted (72.2% vs. 98.6%, p<0.001) and higher sputum eosinophil (13.0% vs. 0.5%, p<0.001) compared to healthy controls. There was no statistically difference in OTU numbers and diversity score between asthmatic and non-asthmatic subjects. At phylum level, the difference of OTU relative abundance remained non-significant. Subjects with eosinopihilic asthma (EA) are older and have shorter duration of asthma (9.6 vs. 19.2 years, p=0.041) as well as lower FEV1% (69.3% vs. 79.2%, p<0.001) compared to subjects with non-eosinopihilic asthma (NEA). The highest OTU numbers (183.9 vs. 142.7 vs. 127.2) and diversity scores, including chao index (318.6 vs. 203.1 vs. 190.8) and ace index (419.8 vs. 251.0 vs. 218.5), were found in NEA group, followed by healthy and EA group. At phylum level, EA subjects had higher abundance of Firmicutes (33.7% vs. 27.5%, p=0.099) but lower Proteobacteria (27.5% vs. 35.2%, p=0.090) compared to NEA subjects, although the differences were not significant.
Conclusions: Patients with eosinophilic asthma have an altered microbial composition in the respiratory tract compared with subjects with non-eosinophilic asthma.The corresponding biological effect on airway inflammation remains to be determined.