STEVE GSCHMEISSNER/SCIENCE PHOTO LIBRARY
Evidence is growing that bacteria can cause bowel cancer. Two kinds of microbes that are found in colon tumours have been shown to cause cancers in mice.
The two commonly found species, Escherichia coli and Bacteroides fragilis, together cause DNA damage that could lead to cancer-causing mutations, although it has not yet been shown they do the same in people.
Cynthia Sears of the Bloomberg-Kimmel Institute for Cancer Immunotherapy in Baltimore, Maryland, and her team found that E. coli and B. fragilis were invading the colon wall in tissue samples taken from people with an inherited form of colon cancer. These species have also previously been found in the more common non-inherited form of bowel cancer, at a higher rate than in healthy colon samples.
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When the two species were put into mice predisposed to get bowel cancer, they dramatically increased the number of tumours that formed.
A third species of bacteria has also been implicated in bowel cancer previously. “There could be particular bacteria that start the process and other bacteria that pile on and make it worse,” says Sears.
Journal reference: Science, DOI: 10.1126/science.aah3648