To assess the impact of sanitation of a living environment on gut microbiota and development of the immune system, we raised BALB/c mice under three distinct environmental conditions: a specific pathogen-free animal room (SPF), a general animal room (XZ) and a farmhouse (JD). All other variables like diet, age, genetic background, physiological status and original gut microbiota were controlled for in the three groups. Using high-throughput sequencing of the 16S rRNA gene, we found that each mouse group had a specific structure of the gut microbial community. Groups JD and XZ harboured a significantly more diverse and richer gut microbiota than did group SPF. Bacteroidetes were significantly more abundant in groups XZ and JD than in group SPF, whereas Firmicutes showed the inverse pattern. Total serum immunoglobulin E (IgE) levels were significantly lower in groups XZ and JD than in group SPF. There were no significant differences in gut microbiota diversity and serum IgE concentration between groups JD and XZ, but we found higher abundance of dominant genera in the gut microflora of group JD. We conclude that exposure to soil, house dust and decaying plant material enhances gut microbial diversity and innate immunity. Our results seem to provide new evidence supporting the hygiene hypothesis.

Exposure to an unsanitary environment increases the diversity and alters the composition of gut microbiota. To identify the key element in the unsanitary environment responsible for this phenomenon, we investigated the effect and the extent by which the soil in our environment influenced the composition of gut microbiota. Results show that adding unsterile or sterile soil to bedding, either before birth or after weaning, influences significantly the composition of mice gut microbiota. Specifically, unsterile soil increases the richness and biodiversity of gut microbiota. Interestingly, based on UniFrac distance analysis of 16S rRNA sequences, the impact of soil on gut microbiota is comparable to that exerted by diet. These findings provide a potential new strategy for intervening on the human gut microbial community and preventing disease.

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BackgroundTraditional farm environments provide protection from allergic diseases. In this study, farm environmental factors were classi ed into three categories: environmental microbes, soil, and organic matter. To explore the impact of soil and environmental microorganisms on gut microbiota and immune function, mice were fed sterilized soil, soil microbes (in lieu of environmental microbes), or non-sterilized soil. ResultsMetagenomic sequencing results showed that the intake of sterile soil while inhaling a small amount of soil microbes in the air, increased gut microbial diversity and the abundance of type III secretion system (T3SS) genes and decreased total serum IgE levels induced by 2-4-dinitro uorobenzene. The intake of soil microbes increased the abundance of genes involved in the metabolism of short-chain fatty acids and amino acid biosynthesis. By contrast, the intake of soil increased gut microbial diversity, the abundance of T3SS genes and related infectious elements, and genes associated with the metabolism of short-chain fatty acids and amino acid biosynthesis and decreased serum IgE levels. The immune function was positively and signi cantly correlated with the bacterial secretion system genes, especially with that of T3SS. ConclusionsAn important mechanism through which farm environments exert a protective effect against allergic diseases could be by serving as a "prebiotic" promoting the reproduction and growth of some intestinal microorganisms that harbor bacterial secretion system genes, especially those of T3SS, whose abundance was positively and signi cantly correlated with innate immune function of mice.

Summary Environmental exposure to low cleanliness prevents the occurrence of allergic diseases and increases the richness and diversity of the intestinal microbiota. Antibiotics are widely used in clinical infection therapy but destroy the balance of the gut microbiota. In this study, the effects of cleanliness of the living environment on the gut microbiota are evaluated after administration of antibiotics. The patterns of gut microbiota are compared before and after antibiotic treatment in mice living in a higher standard clean environment with those of mice living in an unclean environment. The results show that dust exposure prevents the reduction in gut microbiota diversity following antibiotic treatment in mice and impaired structural changes in the gut microbiota. Additionally, dust exposure accelerates the recovery of the gut microbiota, regardless of consumption of a high‐fat or normal diet. An unsanitary environment can reduce the effects of antibiotics on intestinal microecology in mice. These findings provide insights into approaches for regulating antibiotic‐induced symbiosis of the gut microbiota and preventing diseases.