Stress induces the translocation of cutaneous and gastrointestinal microflora to secondary lymphoid organs of C57BL/6 mice

Mammals are colonized by a vast array of bacteria that reside as part of the host's microflora. Despite their enormous levels, these microorganisms tend to be restricted to cutaneous and mucosal surfaces. In the current experiment, only a small percentage of non-stressed mice exhibited detectable levels of bacteria in their inguinal lymph nodes (ILN), spleen, liver, or mesenteric lymph nodes (MLN). However, after experiencing repeated social disruption (SDR), a significant increase in the number of animals having bacteria in their ILN and MLN was found. Since SDR involves fighting in which bite wounds on the skin could provide a portal of entry into the host, it was determined whether experimental wounding (full-thickness skin biopsy), chronic restraint (which is a potent stressor that does not disrupt the skin barrier), or wounding combined with restraint would increase the occurrence of bacteria in secondary lymphoid tissues and liver. Wounding did not significantly increase the prevalence of bacteria in the ILN, MLN, or liver. Interestingly, a larger percentage of restrained and restrained plus wounded mice, in comparison to controls, had bacteria in the ILN, MLN, and liver. Although the stressors increased the number of animals that became colonized, the levels of bacteria in the stressed mice were similar to the levels found in the few non-stressed mice that did become colonized. Our results indicate that psychological components of social stress facilitate the translocation of indigenous bacteria into the host, thus identifying an additional facet through which stressors may impact health.