A Gut Bacterium Found Thriving Inside Colon Tumors

For a long time, cancer was thought of as a disease of human cells alone. This 2012 study helped change that view by pointing to an unexpected resident inside colon tumors: a bacterium.

What the researchers did

The team used a technique called RNA sequencing to read all the genetic material present in colorectal cancer tissue and in matched healthy tissue taken from the same patients. After carefully filtering out the human genetic signal, they looked at what microbial sequences remained. They then confirmed their discovery in a much larger group using a precise measurement method called quantitative PCR, covering 99 people in total.

What they found

• One bacterium stood out sharply: Fusobacterium nucleatum, a microbe usually associated with the mouth, was heavily enriched in tumor tissue.
• On average it appeared at about 79 times higher levels in tumors than in the matched healthy tissue, and it was elevated in the great majority of patients examined.
• Higher amounts of the bacterium were associated with cancer that had spread to nearby lymph nodes, hinting at a connection to more advanced disease.

The finding was striking enough that an independent team reported the same discovery at the same time, strengthening confidence in it.

“Fusobacterium nucleatum sequences were present in tumor samples at levels 79-fold higher than in matched normal control tissue.”

This work opened a productive line of research into how the community of microbes living in our gut relates to long-term gut health. It is educational background only and not medical advice.