There’s new evidence that exposure to certain gram-positive environmental bacteria commonly found on farms may play a key role in protecting children against asthma. The findings reported the paper, “Gram-Positive Bacteria and the Inverse Association Between Farm Exposure and Childhood Asthma,” offer fresh insight into a long-observed phenomenon: Children who grow up in farming environments tend to have lower rates of asthma and allergies than their urban counterparts. The paper was published in The New England Journal of Medicine Evidence.
German researchers analyzed mattress dust samples from 1,018 school children participating in the GABRIELA study, the country’s large investigation examining the environmental and genetic causes of asthma. Using bacterial gene sequencing, bioinformatic analysis and mass spectrometry, the team sought to identify the specific microbes and biological mechanisms responsible for the protective effects associated with farm living.
The analysis revealed nine gram-positive bacterial genera that appeared to drive much of the asthma-protective effect. In mediation analyses, a combined score based on these bacteria explained approximately two-thirds of the inverse association between farm exposure and childhood asthma, suggesting these microorganisms are a major factor in the reduced disease risk seen among farm-exposed children.
Importantly, researchers noted that the protective association remained significant even after accounting for exposure to gram-negative farm bacteria, indicating that the beneficial effect was specifically linked to the identified gram-positive microbes.
The study also investigated how these bacteria may influence human health. Bioinformatic analyses identified nine metabolic pathways associated with the beneficial bacterial communities. Several metabolites produced through these pathways were detected in cowshed dust, including kynurenine and xanthine, which can activate the human aryl hydrocarbon receptor as well as α-linoleic acid and stearidonic acid, which interact with the peroxisome proliferator-activated receptor-gamma (PPAR-γ). Researchers said these receptors are known to play important roles in immune regulation and inflammation.
The study further found evidence of gene-environment interactions, showing that genetic variants in human receptor genes influenced how strongly exposure to the bacterial communities affected asthma risk. The study’s authors said this suggests that an individual's genetic makeup may help determine the extent of protection received from environmental microbial exposure.
Although fungi and bacteriophages were also found alongside the beneficial bacteria, researchers determined that these organisms did not independently account for the protective effect.
The study noted that the findings were replicated in independent populations, strengthening confidence in the results and highlighting the potential importance of environmental microbial exposure in shaping childhood immune development.
According to researchers, the study’s findings could pave the way for new prevention strategies that mimic the beneficial effects of farm environments, potentially leading to novel approaches for reducing childhood asthma risk.
