Sputum metagenomics of U-BIOPRED asthma cohort: link to severity and granulocytic inflammation

<b>Background:</b> Using 16srRNA sequence analysis to probe the airway microbiome of patients with asthma has revealed an altered airway microbiome at the taxonomic level when compared to non-asthmatics. This is the first metagenomic sequencing analysis to determine the phylum, genus and species-level difference between asthmatics of different severities. <b>Methods:</b> Induced sputum samples in the U-BIOPRED adult asthma cohort grouping were two severe asthma groups; non-smoking (SAn, n=67) and current and ex-smokers (SAs/ex, n=33), a mild/moderate asthma (MMA, n=24) group and healthy controls (HC, n=23) were analysed by whole genome sequencing of bacterial rDNA. <b>Results:</b> Alpha-diversity at the taxonomic, gene and pathway level was reduced in SAn and SAs/ex compared to MMA and HC, with no significant difference between MMA and HC identified. Alpha-diversity correlated inversely with exacerbations in previous year and sputum neutrophils in SAn. Beta-diversity dissimilarity between groups were also present. Alpha and Beta diversities were stable at one year. Haemophilus influenzae was predominant in SAn, Tropheryma whipplei in SAs/ex whilst in MMA or HC there was an enrichment by Prevotella intermedia. In SAn, Moraxella catarrhalis, Pasteurella unclassified, Neisseria meningitidis and Haemophilus influenzae were positively correlated with sputum neutrophils. In SAs/ex, Tropheryma whipplei was inversely correlated with FEV1, and Moraxella catarrhalis with exacerbations. <b>Conclusion:</b> In severe asthma, reduced bacterial diversity is associated with neutrophilic inflammation, with the predominance and association of different species dependent on smoking status.