Stress & Gut Microbiome
The Human Genome Project revealed that the human body is the habitat of microbial symbionts ten-times more in number than Homo sapiens cells. The recognition of the complex interactional environment between the human and our symbiotic microflora led researchers to name this the 'human microbiome'. In the human gut, the microbiome directly influences biochemical, physiological and immunological pathways and is the first line of resistance to various diseases.
Traveling can act as an environmental stress causing changes in the microbiome composition or its gene expression. This may lead to the transient (as in travelers' diarrhea) or permanent dominance of pathogenic gut bacteria. Recently, it was shown that exposure to a social stressor altered the composition of the intestinal microbiome, indicating stressor-induced immunomodulation. It was demonstrated that stressor exposure changes the stability of the microflora and leads to bacterial translocation. Circulating levels of IL-6 and MCP-1 increased with stressor exposure and these increases were significantly and positively correlated to changes in three bacterial genera (i.e., Coprococcus, Pseudobutyrivibrio and Dorea) in the cecum. This suggested that the microbiome somehow contributed to stressor-induced immunoenhancement. To test the theory, in follow-up experiments, mice were treated with an antibiotic cocktail to determine whether reducing microflora would annul this stressor-induced increase in circulating cytokines. In the antibiotic-treated mice, exposure to the same stressor failed to increase IL-6 and MCP-1 confirming that intestinal microflora were necessary for the observed increase in circulating cytokines.
Future Microbiol. 2012;7(9):1037-1046. © 2012 Future Medicine Ltd.