Over the last decade, multiple studies have examined possible links between groups of microbes and the presence or absence of multiple diseases, including diabetes, multiple sclerosis, autism and inflammatory bowel disease. But on an individual basis, it’s been unclear which microbes are innocent bystanders, mere markers of disease, and which are active agents, causing harm or providing protection.
Scientists from Harvard Medical School and Boston Children’s Hospital have now designed and successfully used a method to tease out cause-and-effect relationships within the microbiome. Their work, conducted in mice, was described Dec. 6 in Nature.
“Our approach can help scientists find the proverbial needles in a ‘haystack’ of thousands of microbes that are currently thought to modulate health,” said investigator Dennis Kasper, MD, professor of microbiology and immunobiology at HMS.
Tracking bacterial influencers
Kasper and Neeraj Surana, MD, PhD, an infectious disease specialist at Boston Children’s and an HMS instructor in pediatrics, investigated two groups of mice. One group was highly prone to intestinal inflammation, or colitis. The other — harboring human intestinal microbes — had little or no disease. But after the mice were housed together, the first group became less prone to severe symptoms and the second became more prone.
The researchers then compared the microbial profiles of each group before and after co-housing to see what changed in the microbiome and which organisms tracked with colitis severity. This led the discovery of a new organism that tames intestinal inflammation and protects against severe colitis. Dubbed Clostridium immunis, it could be worthy of testing as a probiotic for inflammatory bowel disease.
“The ultimate goal is to clarify the mechanisms of disease and then identify bacterial molecules that can be used to treat, reverse or prevent it,” said Surana.