Gut bacteria Escherichia coli (E. coli) could be responsible for bowel cancer, due to a toxin it produces. Researchers from Harvard University have shown exposing gut cells to this toxin, colibactin, results in damage to the DNA of the exposed cells. While it is as yet unconfirmed if this damage can, or does, lead to cells becoming cancerous, there is good existing evidence that DNA destruction is cancer causing.
Source: New Scientists
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