Researchers have known for a while that stress can play a major role in the gut microbiome, affecting bacteria growth and eventually leading to inflammation and mental-health issues like depression and anxiety. But a new study took things a step further, discovering a bacteria trio that might also function as a diagnostic tool for post-traumatic stress disorder (PTSD).

“Our study compared the gut microbiomes of individuals with PTSD to that of people who also experienced significant trauma but did not develop PTSD,” said lead researcher Stefanie Malan-Müller, PhD, in a press release. “We identified a combination of three bacteria—Actinobacteria, Lentisphaerae, and Verrucomicrobia—that were different in people with PTSD.”

In the study, those with PTSD had much lower levels of the three bacteria varieties than those who experienced trauma but didn’t develop the disorder. Additionally, those who dealt with trauma in their younger years had low levels of two of the three types as well.

“Fully understanding PTSD could contribute to better treatments, especially since the microbiome can easily be altered with the use of prebiotics, probiotics, and synbiotics, or dietary interventions.” —Dr. Malan–Müller, researcher

“What makes this finding interesting is that individuals who experience childhood trauma are at higher risk of developing PTSD later in life, and these changes in the gut microbiome possibly occurred early in life in response to childhood trauma,” Dr. Malan-Müller said.

Since the bacteria in question are specifically responsible for helping the immune system work properly, Dr. Malan-Müller thinks their low levels leads to an increase in inflammation for PTSD sufferers. But it’s still unclear whether the shortfall of bacteria increased the chances of developing PTSD or simply occurred as a result of the disorder.

Still, Dr. Malan-Müller said the discovery brings research closer to fully understanding PTSD, which could “contribute to better treatments, especially since the microbiome can easily be altered with the use of prebiotics, probiotics, and synbiotics, or dietary interventions.”

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