The DNA-damaging bacterium Escherichia coli that flourishes in the digestive tracts of mice afflicted with inflammatory bowel disease has been linked to cancer. Scientists found that the microbiome plays a part in cancer.
The researchers published their findings in the journal Science. There are trillions of microbes in the human gut that can potentially contribute to obesity and the risk of diseases like diabetes.
Mice that have an inflammatory bowel disease contain higher proportions of toxin-producing bacteria, which could lead to colorectal cancers. People with this kind of cancer are more likely to harbor these bacteria.
This opens a broader avenue for cancer researchers since the microbiome can be found elsewhere in the body, and could also initiate tumors there. Tinkering with it might help prevent cancers. The pathogenic bacterium Helicobacter pylori is at the root of most peptic ulcers, which can lead to stomach cancers. Viruses turn infected cells cancerous as a means of spreading their genetic material.
Escherichia coli is a common gut bacterium and can cause cancer when the gut is inflamed. Christian Jobin, a microbiologist at the University of North Carolina at Chapel Hill, and lead author states that patients with inflammatory bowel disease may develop colorectal cancer at rates several times higher than people without troubled stomachs.
The team reared mice with a mutation that made them susceptible to inflammatory bowel disease in germ-free cages. Then, they were moved to cages where mice teeming with bacteria had previously lived. Five months later, all of the mutant mice had developed bowel disease, and 60-80% had colon cancer.
These mice had also developed a different gut microbiome, with a much higher proportion of E. coli, including the E. coli NC101 strain that has been linked to aggressive forms of bowel disease and makes a colibactin, which damages DNA.
Many humans have also bacteria that produce colibactin. There are found in the stools of 20% of healthy people, 40% of people with inflammatory bowel disease and 66% of people of colorectal cancer.
It’s not clear yet how colibactin-producing bacteria are linked to cancer. Jobin hypothesizes that the gut inflammation causes colibactin-producing bacteria to bloom while simultaneously weakening epithelial cells lining the gut, making them more susceptible to DNA damage. If this is sustained, then a cell can turn cancerous.
This could lead to DNA sequencing of microbiomes by doctors to search for bacteria that cause cancer and eliminate them with antibiotics. Similarly, probiotics could displace these microbes.
Reference: “Intestinal Inflammation Targets Cancer-Inducing Activity of the Microbiota” by Janelle C. Arthur, Ernesto Perez-Chanona, Marcus Mühlbauer, Sarah Tomkovich, Joshua M. Uronis, Ting-Jia Fan, Barry J. Campbell, Turki Abujamel, Belgin Dogan, Arlin B. Rogers, Jonathan M. Rhodes, Alain Stintzi, Kenneth W. Simpson, Jonathan J. Hansen, Temitope O. Keku, Anthony A. Fodor and Christian Jobin, 16 August 2012, Science.