Impact of Environmental Microbes on the Composition of the Gut Microbiota of Adult BALB/c Mice.

To investigate the impact of microbes within the living environment on the gut microbiota of adults, we raised three groups of BALB/c mice from 3-4 weeks age in the same specific-pathogen-free animal room for 8 weeks. The control group lived in cages with sterilized bedding (pelletized cardboard), the probiotics group had three probiotics added to the sterilized bedding, and the intestinal microbes (IM) group had the intestinal microbes of a healthy goat added to the bedding. All other variables such as diet, age, genetic background, physiological status, original gut microbiota, and living room were controlled. Using high-throughput sequencing of the 16S rRNA gene, we observed that the control and probiotics groups had similar diversity and richness of gut microbiota. The two groups had significantly lower diversity than the IM group. We also observed that the IM group had a specific structure of gut microbial community compared with the control and probiotics groups. However, the dominate bacteria changed slightly upon exposure to intestinal microbes, and the abundance of the non-dominate species changed significantly. In addition, exposure to intestinal microbes inhibited DNFB-induced elevation of serum IgE levels. Our results provide new evidence in support of the microflora and hygiene hypotheses

Comparison of OTU-levels in the gut microbiota between the control, probiotics, and intestinal microbes groups.

<p>(n = 8; *<i>p <</i> 0.05, **<i>p <</i> 0.01, based on a two-tailed least significant difference test).</p

Correlation between microbial richness/diversity and dermatitis severity indices and other variables.

<p>Correlation between microbial richness/diversity and dermatitis severity indices and other variables.</p

Heat map profiles and dendrograms of the most abundant OTUs in the gut microbiota for all samples.

<p>Experimental groups: control, probiotics, and intestinal microbes. Color represents relative abundance.</p

Effects of exposure to different concentrations of microbes.

<p>(A) Total serum IgE levels; (B) Dermatitis scores of rostral back and ear in BALB/c mice treated with DNFB. Serum absorbance in each group was averaged and each bar represents mean ± SEM (n = 10; *<i>p <</i> 0.05, **<i>p <</i> 0.01, based on a two-tailed least significant difference test).</p

Principal coordinates analysis (PCoA) of unweighted and weighted UniFrac distances.

<p>These are for the fecal microbiota of the three experimental mice: control, probiotics, and intestinal microbes. Analysis was based on the Illumina bacterial 16S rRNA gene dataset (V4 region).</p

Comparison of bacterial richness and diversity among Control, Probiotics, and Microbes.

<p>Control mice were raised in cages with sterilized pelletized cardboard bedding, probiotics mice were raised in cages sterilized pelletized cardboard bedding added with probiotics, and intestinal microbes mice were raised in cages added with goat intestinal microbes. (A) Rarefaction curves showing unique operational taxonomic units (OTUs) (a box graph at the rarefied sequence number). (B) Chao1 estimators. (C) Phylogenetic diversity (PD). (D) Shannon index. (n = 8; * p < 0.05, ** p < 0.01, based on a two-tailed least significant difference test).</p