Exposing mice to bacteria that help regulate the immune system can help to prevent stress from causing harmful inflammation, and in some cases, illness, reports a scientific team in the May 31, 2016 issue of Proceedings of the National Academy of Sciences.

The findings support the idea that “reintroducing” humans to certain bacteria may promote health and wellness, the researchers said.

Previous research shows that inflammatory diseases such as inflammatory bowel disease and colitis are becoming increasingly more common in modern societies. According to “the hygiene hypothesis,” increased levels of cleanliness in our urban lives have made us lose touch with the good microbes in the environment, “the old friends” we’ve evolved with, and as a result, we are less able to rely on our immune system to protect us against inflammatory diseases.

Risk for psychiatric disorders ranging from depression to PTSD to schizophrenia is thought by some scientists to be linked to elevated levels of inflammation.

In the new study, researchers investigated how stress acts on the normal relationship between the body and the microbial community occupying the body, which is collectively called the microbiota. They showed that stress disrupts this relationship, resulting in elevated inflammation.

The researchers injected mice with a bacterium called Mycobacterium vaccae, which is abundant in soil and has immune system-regulating effects. (Immunoregulation is the control of specific immune responses and interactions between immune cells, particularly those resulting in a balanced production of different classes of T cells that promote and suppress inflammation.) The bacteria were prepared in a way that made it impossible for them to proliferate in the body and thereby infect the animals, but could still, nevertheless, affect the immune system.

This prevented mice from getting colitis when put in highly stressful situations. In stressed mice, the treatment had anti-anxiety and fear-reducing effects, the researchers found. In mice that had inflammatory bowel disease, the bacterial treatment prevented stress-induced aggravation of colitis.

Together, these findings can help researchers develop microbiome- and immunoregulation-based strategies to prevent disorders related to stress, the researchers said.

The team of researchers was led by Christopher A. Lowry, Ph.D., of the University of Colorado Boulder, a NARSAD Young Investigator grantee in 2007 and 2010. It also included Monika Fleshner, Ph.D., of CU-Boulder, a 2005 NARSAD Independent Investigator grantee, and Charles L. Raison, M.D., of University of Wisconsin-Madison, a 2013 NARSAD Independent Investigator grantee.