LATE-BREAKING ABSTRACT: Bacterial microbiota of mattress dust and nasal samples, farming exposure, and childhood asthma

Background: Asthma is associated with environmental determinants. An environment consistently been related to a lower risk of childhood asthma is the farm. Previously, we found an inverse association between diversity of microbial exposure on farm environments and childhood asthma based on SSCP analysis and cultural data. Aims: To investigate microbiota of the upper respiratory tract and environmental samples from farm and non-farm children of the Austrian part of the GABRIELA study. Methods: The V3-V5 region of bacterial 16S rRNA genes from nasal and mattress dust samples of 86 children was analyzed using 454-pyrosequencing. Community composition on genus level was based on relative abundances, and diversity was determined as species richness. Regression models were used to test for associations with farming or asthma. Geometric mean ratios (GMR) and 95%- confidence-interval (CI) are reported for richness effects. Results: Microbiota of mattress dust is composed of typical skin bacteria and more than one third of rare often unknown genera probably originating from the environment. Farm exposure was strongly associated with a higher diversity in mattress dust (GMR (C.I.): 1.33 (1.18-1.49), p=5.6*10 -6 ). Asthma was inversely associated with diversity in mattress dust (GMR (C.I.): 0.86 (0.77-0.97), p=0.015). A trend for the asthma protective effect of bacterial richness was also seen in the nose microbiota. Additionally, asthma was associated with a lower relative abundance of Prevotella in the nose. Conclusions: We show that a higher bacterial richness in farm environment has a protective effect for asthma, supporting the strong influence of the environment on asthma protection.