Some Colon Cancers May Be Caused by Diarrheal Bacteria

Bacteria that cause diarrhea may also be the cause of some colon cancers, according to research from John Hopkins University. The investigators believe that strains of the common Bacteroides fragilis (ETBF) trick immune systems cells into allowing runaway colon tissue inflammation - a precursor to malignant tumor growth.


Bacteriodes fragilis is a enterotoxigenic bacterium widely known to cause diarrhea in children and adults in the developing and developed world. The bacteria, which typically reside in the gut, can cause no symptoms in some individuals, but others develop diarrhea and colon inflammation.

To find the connection between ETBF and colon cancer, John Hopkins researchers conducted a series of tests in mice bred to carry mutations in a colon cancer-causing gene. Their results show that mice infected with the bacteria developed diarrhea that resolved quickly, but after a week later, developed inflammation and small tumors in the colon.

The researchers also examined the bacteria’s effect on immune responses that may contribute to cancer development. In the infected mice, they found high levels of a protein known to act as a trigger for inflammation. One of these signals activates an immune cell known as Th17. This cell produces molecules known to cause prolonged inflammation of tissues.

In infected mice, Th17 activity was 100 times greater than normal. When researchers blocked the effects of Th17, they were able to reverse inflammation and tumor growth.

Immunologist and cancer researcher of Johns Hopkins, Drew Pardoll, M.D., Ph.D., believes, “If what we are seeing mice holds true in humans the chronic inflammation damages genetic material in the colon cells, allowing them to grow uncontrollably an develop into tumors earlier and more progressively than if they were not infected with
ETBF.”


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