The use of a bacterium might help humans better cope with high-stress disorders like PTSD, according to new CU Boulder research

Rats immunized with a certain bacterium found in soil—Mycobacterium vaccae (M. vaccae)—are able to bounce back better from stressful situations compared to non-immunized rats, according to new research from the University of Colorado Boulder.

These findings from Christopher Lowry, a professor of integrative physiology, have potential implications for the human treatment of posttraumatic stress disorder (PTSD) and depression as they recognize that stress and trauma-related psychiatric disorders have effects throughout the body and treat the "inappropriate inflammation" of the gut that is associated with these anxiety disorders.

The research was published this year in Brain, Behavior and Immunity.

"This research suggests that immunization with M. vaccae has long-term effects on brain function," Lowry states.

Lowry began this line of research in the early 2000s based on a simple question: "How do lungs communicate with the brain?" That question led to his studies designed to understand the intricacies of the human body and the interactions between the body and brain, and the role that bacteria can play in human health.

"Humans co-evolved with bacteria, and some of our physiological functions have been turned over to bacteria," said Lowry, "including functions that are critical for our health and well-being."

Lowry's research employed the "fear-potentiated startle test," which measured "fear extinction"—or the disappearance of fear—in rats, and seeing if treatment with M. vaccae could boost stress resilience, or the ability to cope with stress from the external environment.

The rats are given a mild foot-shock while simultaneously being exposed to a bright light that shines while the shock is administered. The rats learn to associate the light with the shock. Subsequently, rats show fear when the light alone, without the shock, appears.

"They remember that the light is a cue for the shock," Lowry says. Rats that were not immunized "maintained their fear (of the light), whereas the immunized rats more rapidly extinguished their fear. The idea that you can accelerate fear extinction in this way is pretty exciting."

Lowry intends to pursue approval from the U.S. Food and Drug Administration for use of M. vaccae in humans. This will be done in collaboration with research teams at the U.S. Department of Veterans Affairs. The VA is involved because of the potential to help the population of veterans suffer from PTSD.

Lowry’s lab is also studying serotonin neurons, or the happiness transmitters of the brain. He has found that fear conditioning, like that in the rat experiment, can alter the genetics of the neurons that produce serotonin.

These findings also support a recent publication by Lowry and colleagues at Stellenbosch University in South Africa that shows that individuals with PTSD have a relatively low abundance of three groups of bacteria, including Actinobacteria, the group to which M. vaccae belongs, within the collection of microorganisms that inhabit the human gut.

"The microbiome field is exploding," Lowry states. "It is a very hot topic right now. Nearly every day there is some new development related to microbiomes."

Microbiome research breaks down traditional barriers between psychiatry, physiology, immunology, endocrinology and neurology. As the silos of study break down, different disciplines build from each other, which is increasing the complexity of these studies.

"In modern urban environments, we have reduced exposure to microorganisms that serve to limit inappropriate inflammation," Lowry states. This reduced exposure is thanks to the overuse of antibiotics and disinfectants that can limit the good bacterium along with the bad.

"Our findings suggest that replacing just one of these bacteria can return things to normal, so to speak."