Exacerbation of allergic rhinitis by the commensal bacterium Streptococcus salivarius

Allergic rhinitis (AR)—commonly called hay fever—is a widespread condition that affects the quality of life of millions of people. The pathophysiology of AR remains incompletely understood. In particular, it is unclear whether members of the colonizing nasal microbiota contribute to AR. Here, using 16S ribosomal RNA sequencing, we show that the nasal microbiome of patients with AR ( n = 55) shows distinct differences compared with that from healthy individuals ( n = 105), including decreased heterogeneity and the increased abundance of one species, Streptococcus salivarius . Using ex vivo and in vivo models of AR, we demonstrate that this commensal bacterium contributes to AR development, promoting inflammatory cytokine release and morphological changes in the nasal epithelium that are characteristic of AR. Our data indicate that this is due to the ability of S. salivarius to adhere to the nasal epithelium under AR conditions. Our study indicates the potential of targeted antibacterial approaches for AR therapy.