Soil bacterium could help combat stress, psychiatric problems

Bacterium naturally found in soil may have healing effects when prepared as an immunization, according to a new study.

The study, “Immunization with a heat-killed preparation of the environmental bacterium Mycobacterium vaccae promotes stress resilience in mice,” was published in the Proceedings of the National Academy of Sciences. It revealed that when mice were injected with Mycobacterium vaccae (M. vaccae NCTC 11659), stress resilience and coping behaviors were improved, and stress-induced colitis was prevented.

Mice given a heat-killed preparation of the bacterium were half as likely to display flight or avoidance behaviors when confronted by an aggressor in the short-term period after injection, and showed decreased levels of submissive behaviors for up to two weeks later, according to the study.

Stress-induced colitis, an irritable bowel disease, was also reduced in mice injected with the bacterium. Researchers saw a 50% reduction in the condition in the treated mice, measured by cellular damage to the colon and infiltration of immune cells.

Christopher A. Lowry, PhD, an associate professor in the department of Integrative Physiology at the University of Colorado Boulder and the senior author of the new research, says the results of the study point toward common mechanisms underlying vulnerability to stress-related psychiatric disorders, allergies, asthma and autoimmune conditions.

“Our research shows that stress causes a dramatic reduction of diversity of the gut microbiome, along with a dramatic change in the composition of the gut microbiome, favoring expansion of pathobionts associated with colitis and autoimmunity,” Lowry tells Medical Economics. “Our data suggest that vulnerability to stress-induced colitis is exaggerated in the absence of inadequate immunoregulation. This vulnerability may be mitigated by use of immunoregulation-promoting probiotics or, in our case, immunization with heat-killed preparations of bacteria that have immunoregulatory properties. By ‘immunoregulation,’ we mean the balanced expansion of proinflammatory effector T-cell populations and anti-inflammatory regulatory T cells (Treg), a balance that is under the control of microbial inputs.”

An injection of M. vaccae would not target an antigen as a traditional vaccine would, but instead activates immunoregulatory responses to protect against inflammation.

The power of microbiomes

Researchers found that mice who were given a heat-killed preparation of M. vaccae responded with approximately half as many flight and avoidance behaviors when challenged by an aggressor, as compared to untreated mice, during the first hour of the experiment. The immunized mice continued to show decreased levels of submissive behaviors one to two weeks after treatment. 

The research underscores the importance of an organism’s microbiome in preventing and coping with inflammation-related diseases and psychiatric conditions. Microbiomes are made up of teeming communities of microorganisms, including environmental bacteria. A microbiome’s diversity is increasingly recognized to play key roles in immunoregulation—controlling autoimmune and allergic responses, decreasing vulnerability to infection, and other regulatory health functions. Previous research has suggested that stress-related conditions such as posttraumatic stress disorder (PTSD) may be due to a failure of immunoregulation.

There are theories, according to the research team, that individuals today are exposed to so few environmental bacteria and immunoregulatory organisms because of modern sanitary measures and antibiotics, that human microbiomes are now insufficient and unable to suppress inflammation.