Characterization of the oral mycobiome of Portuguese with allergic rhinitis and asthma

Allergic rhinitis and asthma are two prevailing chronic airway diseases and serious public health concerns. Previous research has already described the role of the airway bacteriome in these two diseases, but almost no study so far has explored the mycobiome and its possible association to airway inflammation. Here we sequenced the internal transcribed spacers (ITS) 1 and 2 to characterize the oral mycobiome of 349 Portuguese children and young adults with allergic rhinitis alone (AR) or with asthma (ARAS), asthmatics (AS) and healthy controls (HC). Our genomic analyses showed that the two most abundant fungal phyla (Ascomycota and Basidiomycota) and 3–5 of the 14 most abundant fungal genera (Cladosporium, Aspergillus, Aleurina, Candida and Rhodotorula) in the mouth differed significantly (P ≤ 0.04) between both rhinitic groups and HC. However, none of the same taxa varied significantly between the three respiratory disease groups (AR, ARAS and AS). The oral mycobiomes of respiratory ill patients showed the highest intra-group diversity (microbial richness and evenness), while HC showed the lowest, with all alpha-diversity indices varying significantly (P ≤ 0.0424) between them. Similarly, all disease groups showed significant differences (P ≤ 0.0052) in microbial structure (i.e., beta-diversity indices) when compared to HC samples. Thirty metabolic pathways (PICRUSt2) were differentially abundant (Wald's test) between AR or ARAS and HC patients, but only one of them (D-galactose degradation I) was over abundant (log2 Fold Change >0.75) in the ARAS group. Spiec-Easi fungal networks varied greatly among groups, which suggests chronic respiratory allergic diseases may alter fungal connectivity in the mouth. This study increases our comprehension of the role of the oral mycobiome in allergy-related conditions. It shows for the first time that the oral mycobiota changes during health and allergic rhinitis (with and without asthma comorbidity) and highlights specific taxa, metabolic pathways and fungal interactions that may relate to chronic airway disease.