The bacterial species Fusobacterium nucleatum (Fn) inhabits plaque in the mouth and is rarely found in the gut—except in the case of colorectal cancer, when Fn can be isolated from patients’ stool samples and Fn DNA can be found in tumors. 

In research published online on March 10 in mBio, Libusha Kelly, Ph.D., and colleagues report that Fn is actually composed of six genomically distinct populations that have different body site preferences. After searching through nearly 10,000 samples from 11 studies involving healthy and sick individuals, the researchers found that one particular Fn population, called C2 animalis, commonly occurred in the guts of people with colorectal cancer and Crohn’s disease. In addition, C2 animalis along with Polymorphum, the most common Fn population in the mouth, were prevalent in irritable bowel disease. Polymorphum levels also were significantly increased in Crohn’s stool samples—an effect significantly stronger in males than in females. Since gut levels of C2 animalis in colorectal cancer patients were found to exceed levels in the mouths of healthy people, measuring gut levels of C2 animalis could be useful for assessing colorectal cancer risk. If C2 animalis not only correlates with colorectal cancer risk but plays a role in causing the disease, then specifically targeting this bacterial population with antibiotics might help prevent colorectal cancer from developing.   

Dr. Kelly is an associate professor of systems & computational biology and microbiology & immunology at Einstein, and a member of the National Cancer Institute–designated Montefiore Einstein Comprehensive Cancer Center.