For several years, one particular bacterium has been associated with colorectal cancer: Bacteroides fragilis.

The difficulty is that this bacterium is also present in the vast majority of healthy individuals.

“It has been a paradox that we repeatedly find the same bacterium in connection with colorectal cancer, while at the same time it is a completely normal part of the gut in healthy people,” says Flemming Damgaard, medical doctor and Ph.D. at the Department of Clinical Microbiology at Odense University Hospital and the University of Southern Denmark.