Dust microbiota from the city or the countryside? Atopic dermatitis has a preference!

Atopic dermatitis (or eczema) is the most common chronic skin disease (sidenote: https://www.worldallergy.org/UserFiles/file/WAOAtopicDermatitisInfographic2018.pdf   ) . It is characterized by dry skin and eczematous lesions (redness, itching, etc.), which are non-contagious and develop in flare ups. This condition is the result of a complex interaction between environmental and genetic factors and can show an early onset, even in infants, but can persist or even appear for the first time in adolescents and adults. Among environmental factors, the role of the gut microbiota, but also of the skin and nasal microbiota, has been clearly demonstrated. Despite major research efforts in recent years, the number of people affected by the disease continues to grow worldwide. What explains this increase? Initial explanations point to environmental changes resulting from improved hygiene and urbanization. Surprisingly, rates of the disease in African countries seem quite low, whereas African Americans are more affected. This new study sought to understand why this is so. To this end it analyzed the links between dust microbiota in rural and urban homes and the development of the condition in South African children.

Urban dust and rural dust: what does the microbiota tell us?

The researchers scoured the homes (rural and urban) of 86 South African children aged 12 to 36 months with and without atopic dermatitis. Their goal? To collect dust samples in order to analyze the bacterial microbiota contained therein. Their first finding was that there was a significant difference between dust from urban and rural homes in terms of overall microbial composition. Dust from urban homes had significantly lower bacterial diversity than that of rural homes. There was also a lower abundance of specific bacteria (Clostridia, Lachnospiraceae, Ruminococcaceae and Bacteroidaceae).

Bacteria that protect against atopic dermatitis?

Another finding of the study was that the composition and diversity of the dust bacteria differed between the homes of affected and unaffected children. Dust in the homes of unaffected children living in the countryside had a higher relative abundance of bacteria from the Clostridia, Ruminococcaceae and Bacteroidaceae bacterial families. This suggests that these bacteria may have a protective role against atopic dermatitis. In contrast, in urban environments, no difference was observed in the abundance or diversity of dust bacteria between the homes of affected and unaffected children.

The bacterial composition of house dust may therefore be an important risk factor for the development of atopic dermatitis, and this association may be driven in part by the gut microbiome. Unknowingly, young children ingest and inhale house dust on a daily basis. According to the researchers, it is likely that some of the bacteria present in this dust reach the gut, potentially protecting children against eczema.