Farm exposure protects from childhood asthma through seven Gram-positive bacterial genera

The protective effect of farm exposure on asthma and atopic conditions has been attributed to the diversity of environmental bacteria and fungi but the specific taxa and the underlying mechanisms remain elusive.In the framework of this project, from the highly diverse microbial exposure in a farm environment, we identified seven Gram- positive bacterial genera, whose composite score explained 80% of the protective farm effect on asthma in mediation analysis. The effect was independent of Gram-negative and farm-associated bacteria. Moreover, we identified bacterial metabolic pathways and confirmed the presence of their metabolites in cow shed and mattress dust samples by mass spectrometry. Finally we found gene-environment interactions for asthma with a compound score of the 7 taxa interacting with SNPs related to the three human receptors recognizing the identified metabolites.