A species of gut bacteria could ease anxiety and diarrhea-predominant IBS

Irritable bowel syndrome (IBS) is a condition characterized by abdominal pain, bloating and changes in bowel movements, estimated to affect between 10% and 15% of people worldwide. Past studies suggest that in many cases this condition is accompanied by anxiety, an emotional state marked by worry, fear and/or overthinking about specific life events.

While IBS and anxiety are known to often occur together, the biological processes linking the two have not yet been fully elucidated. One possibility is that bacteria and other microorganisms living in the digestive tract, broadly referred to as gut microbiota, contribute to these biological processes.

Researchers at Wuhan University of Science and Technology and Huazhong University of Science and Technology carried out a study aimed at shedding more light on the biological mechanisms linking a type of IBS called diarrhea-predominant IBS (IBS-D), which is associated with frequent loose stools, with anxiety.

Their paper, published in Translational Psychiatry, suggests that a species of gut-inhabiting bacteria called Phocaeicola vulgatus could contribute to easing anxiety associated with IBS-D.

“In clinical practice, we frequently observed high anxiety prevalence among patients with IBS-D,” Bai Tao, senior author of the paper, told Medical Xpress.

“While several studies have suggested gut microbiota exerts important influences on gut-brain interaction disorders, the underlying mechanisms remain largely uncharacterized. This drove us to carry out the study, which aimed to elucidate the neuropathological basis of anxiety in IBS-D and identify potential microbiota-based therapeutic targets.”

Exploring the link between IBS and anxiety

To explore the biological mechanisms linking anxiety and IBS, Tao and his colleagues collected clinical data from a group of patients experiencing IBS-D. Approximately 35% of these patients also reported feeling anxious, while the rest did not.

Notably, for patients who also reported feeling anxious, more intense anxiety was linked with worse IBS-D symptoms. In brain scans collected from anxious patients, the researchers also observed anomalous neural activity in the amygdala, a small almond-like region deep in the brain known to control fear, other intense emotions and automatic responses to threats.

“We then built a stress mouse model that copied human IBS and anxiety symptoms,” Tao explained. “Fecal microbiota transfer confirmed gut bacteria alone triggered both gut pain and anxious behaviors in mice. We found Phocaeicola vulgatus was much less abundant in both patients and model mice; lower levels linked to worse anxiety and impaired amygdala function.”

The researchers also carried out a series of genetic analyses on their mouse model of IBS to further explore the effects of the Phocaeicola vulgatus bacteria. The results of these analyses confirmed that the bacteria protected the mouse brain from anxiety.

“Finally, giving live Phocaeicola vulgatus to mice eased anxiety by calming brain inflammation and repairing damaged neurons in the amygdala,” Tao said.

Informing future IBS treatment

The results of this study are still preliminary, yet they hint at the potential of Phocaeicola vulgatus bacteria as a treatment for IBS-D accompanied by anxiety. Future research could further explore how this specific type of bacteria influences neuroinflammation and activity in the amygdala.

“We found that Phocaeicola vulgatus is depleted in IBS-D patients and anxious model mice, and genetically it protects against anxiety,” Tao said.

“Supplementing this bacterium alleviates anxiety by easing amygdala neuroinflammation and repairing impaired neurons. This study provides a novel psychobiotic treatment idea for IBS patients with anxiety, and bilateral amygdala brain signals can act as a biomarker for comorbid anxiety in IBS-D.”

If the therapeutic potential and safety of Phocaeicola vulgatus is confirmed in clinical studies, this recent work could pave the way for the introduction of promising new treatments for specific types of IBS. As part of their next studies, Tao and his colleagues plan to assess the potential of specific treatments based on strains of Phocaeicola vulgatus.

“We will explore the specific metabolites of Phocaeicola vulgatus that cross the blood-brain barrier to regulate brain inflammation,” Tao added. “We also plan to develop safer postbiotics (i.e., beneficial waste products left behind when healthy gut bacteria digest fiber or multiply) instead of live bacteria, to avoid infection risks.”

Who’s behind this story?

Ingrid Fadelli

Freelance journalist with BSc Psychology and MA International Journalism. Covers AI, robotics, neuroscience, and astrophysics since 2018.

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Sadie Harley

BSc Life Sciences & Ecology. Microbiology lab background with pharmaceutical news experience in oil, gas, and renewable industries.

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Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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