Features and clinical significance of airway microbiota in patients with neutrophilic asthma

Abstract

Objective To explore the characteristics and clinical significance of airway microbiota in the patients with neutrophilic asthma. Methods Induced sputum samples were collected from 44 patients with clinically stable neutrophilic asthma attending the second Affiliated Hospital of Army Medical University from August 2019 to January 2020. After DNA extraction, 16S rRNA and internal transcribed space (ITS) sequencing were performed by PacBio Sequel Systems. Two subgroups were identified by hierarchical cluster analysis on sequencing data, and the differences in their bacterial and fungal microbiota and clinical characteristics were explored. Results Hierarchical clustering analysis of bacterial sequencing data from 44 subjects identified 2 clusters. Compared to the larger cluster (group A1, n=32), the smaller cluster (group A2, n=12) was characterized by a predominance of Haemophilus in their bacterial microbiota, and the patients in this group demonstrated a higher percentage of sputum neutrophils (Z=-4.14, P < 0.001) and poorer FEV1% pred (t=2.15, P=0.037). In bacterial microbiota, there were significant differences in both α-diversity (Chao1 and Simpson indexes, P < 0.001) and β-diversity (Adonis, R2=0.290, P=0.001) between the 2 groups. At the species level, LEfSe analysis revealed that the group A1 was significantly enriched in Streptococcus pneumonia, Haemophilus parainfluenzae, Fusobacterium nucleatum, Lautropia mirabilis, Neisseria meningitides, Porphyromonas gingivalis, Prevotella melaninogenica, Prevotella pallens and Ralstonia solanacearum, while the group A2 was enriched in Haemophilus influenzae. In fungal microbiota, no significant differences were observed between the 2 groups in α-diversity (Chao1 index, P=0.230; Simpson index, P=0.097), whereas significant differences were observed between their β-diversity (Adonis, R2=0.068, P=0.002). At the species level, LEfSe analysis revealed that the group A1 was enriched in Schizophyllum commune, and group A2 was enriched in Trametes versicolor and Irpex lacteus. Interaction network analysis indicated that group A2 showed more correlations between genus than group A1, and the strength of association between genus was more intense. Conclusion Among the patients with stable neutrophilic asthma, there is a subgroup characterized by the presence of Haemophilus influenzae as its airway predominant colonizing bacteria, which differs significantly from the non-Haemophilus influenzae dominant group in terms of bacterial and fungal microbiota, and presents clinical characteristics with more severe airway inflammation and poorer lung function.

Keywords

• neutrophils
• asthma
• induced sputum
• microbiota