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Bacteria was here long before us, will be here long after us, and never stops serving up secrets about how it affects us. A new study just revealed another big one concealed by bacteria living in the dirt beneath us that may bring us closer to the development of the long-theorized “stress vaccine."

In 2018 a research team led by Christopher Lowry, Integrative Physiology Professor at the University of Colorado Boulder, published a study showing that a soil-based bacterium called Mycobacterium vaccae decreased reactions in mice. The researchers injected the rodents with M. vaccae prior to exposing them to a stressful event, and the shots both prevented a “ -like syndrome” in the short-term and diminished stress reactions later on.

That study helped build out the hypothesis that M. vaccae harbors compounds that tune down the flight-or-fight response in mammals, but why or how the effect occurred was still a mystery.

Fast-forward to 2019, and a new study authored by Lowry and his team has identified and isolated a (aka lipid) in the bacterium that appears responsible for the effects. Going a step further, the team was also able to chemically synthesize the lipid to deconstruct how it interacts with immune cells.

“We knew it worked, but we didn’t know why,” said Lowry in a press statement. “This new paper helps clarify that.”

The researchers report that the lipid binds with receptors inside the immune cells and locks out certain chemicals that cause inflammation. When they “pretreated” cells with the lipid and then attempted to stimulate an inflammatory response, they found that the cells were resistant to the effects. In other words, the cells were effectively vaccinated against inflammation.

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“It seems that these bacteria we co-evolved with have a trick up their sleeve,” said Lowry. “When they get taken up by immune cells, they release these lipids that bind to this receptor and shut off the inflammatory cascade.”

What does this mean for us? If the idea of a human stress vaccine that leverages beneficial bacteria has merit, this finding is crucial to making it a reality. The lipid could become the focus for drug development, and perhaps not only to prevent stress reactions that lead to disorders like PTSD, but also to undermine other kinds of inflammatory reactions.

“This is a huge step forward for us because it identifies an active component of the bacteria and the receptor for this active component in the host,” Lowry said.

Lowry added that the additional big news is that M. vaccae is hardly the only soil-based bacterium holding secrets.

“This is just one strain of one species of one type of bacterium that is found in the soil but there are millions of other strains in soils,” Lowry said. “We are just beginning to see the tip of the iceberg in terms of identifying the mechanisms through which they have evolved to keep us healthy. It should inspire awe in all of us.”

For now this is still research in mice, so we’re not necessarily close to human tests, but we are closer to the possibility. These studies show remarkable progress in a short span of time. With more research underway, we could be talking about stress vaccine clinical evaluations sooner than later.

Taking that step, however, should entail important discussions about the implications of "turning off" the stress response. We already know the significant downsides of drugs like benzodiazepines and other types of , both in terms of their abuse potential and other ways they affect the brain. How this approach will be differentiated from those is a critical topic, one that deserves consideration as we near the doorstep of developing new with potential to both help and harm.

The latest study was published in the journal Psychopharmacology.

© David DiSalvo