A large international analysis suggests that a previously overlooked group of gut bacteria may be closely linked to overall health.
In a study published in Cell Host & Microbe, researchers examined gut microbiome data from more than 11,000 people across 39 countries and found that levels of a bacterial group known as CAG-170 were consistently higher in people without chronic disease. Lower levels of these microbes appeared across a wide range of conditions, including inflammatory bowel disease, obesity, multiple sclerosis and chronic fatigue syndrome.
CAG-170 bacteria are part of what scientists call the “hidden microbiome.” Unlike many familiar gut microbes, most members of this group have never been grown in a lab and are known only through their genetic signatures. Using large-scale genomic databases and computational analysis, researchers were able to track these bacteria across thousands of samples and populations.
The pattern held up across multiple approaches. When researchers compared healthy individuals with those living with disease, CAG-170 was repeatedly one of the strongest markers distinguishing the two groups. People with signs of gut imbalance, known as dysbiosis, were also more likely to have lower levels of these bacteria.
Genetic analysis suggests that CAG-170 bacteria are well equipped to support gut ecosystem function. They appear capable of breaking down a wide range of carbohydrates and fibers, and they may produce vitamin B12 that supports other gut microbes rather than directly benefiting the human host. Researchers believe this role could help stabilize the broader microbiome, supporting digestion and resilience.
“Our work has revealed that CAG-170 bacteria appear to be key players in human health, likely by helping us to digest the main components of our food and keeping the whole microbiome running smoothly,” said Alexandre Almeida, PhD, who led the research at University of Cambridge.
Because CAG-170 bacteria are so consistently linked to health across countries and conditions, the researchers suggest they could eventually serve as a biological indicator of gut health. The findings may also inform the development of future probiotics designed to support these microbes, although translating the results into therapies will require methods to culture and study them directly.
The authors note that while the associations are strong, the study does not prove that CAG-170 bacteria cause better health. Instead, they may reflect broader gut environments that support resilience and metabolic balance. Further research will be needed to understand how diet, lifestyle and environment influence these microbes over time.
This research was supported by a Career Development Award from the UK Medical Research Council. Additional funding came from the Cambridge Centre for Data-Driven Discovery and the Accelerate Programme for Scientific Discovery, supported by a donation from Schmidt Sciences.