LATE-BREAKING ABSTRACT: Bronchial microbiome in severe persistent oral corticosteroid-dependent asthma

Background: Bronchial microbiome has not been studied in severe persistent asthma and its characterization in bronchial mucosa and aspirates is needed Objective: To characterize the bronchial microbiome of oral corticosteroid-dependent asthma patients Methods: bronchial biopsies (BB) and aspirates (BA) were obtained through bronchoscopy; 16S rRNA gene was sequenced and bacterial relative abundances (RA), richness and evenness were compared Results: 13 patients with a mean age of 49 years (SD 14) and a FEV 1 of 72% (55.7-88.5) were included; 11 BB and 12 BA samples were analyzed. Firmicutes, Proteobacteria and Bacteroidetes were the predominant phyla, with Prevotella and Streptococcus as the genera with higher RA in both samples. Bacteroidetes and Fusobacteria phyla showed significantly higher RA in BB than in BA samples [33 (21-35) vs 22 (14-28) p=0.044 and 6.5 (4-11) vs 2 (0.7-5.5) p=0.006, respectively]. 109 out of 364 identified genera showed significant differences between the samples, with higher RA for 73 in BB and 36 in BA samples. Chao 1 richness parameter was higher in BA samples [3038(2422-4564) vs 1741(1318-2072), p vs 6.7 (6-7), p=0.032], confirming that BA community is dominated by some taxa. Bray-Curtis β-diversity parameter and adonis test confirmed that the community structure in BB and BA samples was significantly different (p Conclusions: In severe corticosteroid-dependent asthma, 1) the microbiota of the bronchial mucosa is composed mainly by Firmicutes, Proteobacteria and Bacteroidetes phyla; 2) The BA microbiota is not representative of the bronchial mucosa microbiome Funded by FUCAP, SEPAR and ISCIII.