Presence of Specific Gut Bacteria Can Increase Colon Cancer Risk

Colon polyps, illustration
[Source: Sebastian Kaulitzki/Science Photo Library/Getty Images]

Research from the University of Washington School of Medicine suggests that presence of the bacteria Bacteroides fragilis in precancerous gut polyps could correlate with an increased risk for developing colon cancer.

The team found that individuals with these bacteria present in their polyps had increased inflammation and seemed to induce a pro-inflammatory signalling pathway, which the researchers think could make these individuals more prone to progressing to cancer.

“Growing evidence for the role of the gut microbiota in the initiation of colorectal cancer has sparked interest in approaches that target these microorganisms,” write the researchers in the journal Cell Host & Microbe.

“However, little is known about the composition and role of the microbiota associated with precancerous polyps.”

In this study, William DePaolo, associate professor at the University of Washington School of Medicine, and colleagues studied 40 people aged 50-75 years who underwent routine colonoscopies to check for polyp formation.

Overall, 9 were polyp free and 31 had polyps. In patients with polyps, biopsy data showed high levels of B. fragilis a bacteria found commonly in the gut which is normally considered ‘friendly’ or commensal, but can also cause infections.

The team found that there was a correlation between the level of B. fragilis found in the polyp samples and the level of inflammatory cytokines in the cells around the polyp.

“The enterotoxigenic strain of B. fragilis has been correlated with colorectal cancer in various human studies and mouse models due to oncogenic properties attributed to the expression of the B. fragilis toxin, or bft, while non-enterotoxigenic strains are considered normal healthy commensal bacteria,” write the authors.

The team compared the strain of B. fragilis found in the polyps with that found in the gut of those without polyps. While the researchers did not find bft in the strains seen in this study, the strains in the polyps lacked the fragilysin gene and seemed to trigger the release of high levels of pro-inflammatory cytokines through Toll-like receptor 4 rather than 2.

“The whole idea is that most people look at advanced colorectal cancer and think of the microbiome, but it’s hard to determine if the microbiome has changed and when it changed,” said DePaolo in a press statement. “So we took an earlier look at the disease and asked when might the microbiome may be pushing a polyp toward cancer.”

Although only around 5% of polyps actually turn out to cancerous, the researchers think their findings could be a useful early indicator of which patients might be at highest risk of progressing to cancer. They plan to expand the study to more patients and assess whether using a fecal sample could be an alternative to needing a mucosal biopsy.

This is just one study that shows how changes in the microbiome can influence colorectal cancer risk. Earlier this month another study was published suggesting that sustained use of antibiotics could increase risk of colon cancer, likely through microbiome changes linked to their consumption.

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