A bacterial intestinal toxin that damages DNA may be involved in bowel cancer
Intestinal bacteria may be responsible for intestinal cancer. People with the disease often have higher levels of certain strains of Escherichia coli in their digestive systems. Now, it has been shown that a toxin produced by the bacteria damages DNA in intestinal cells, possibly the first step to becoming cancerous.
While some strains of E. coli can cause food poisoning, others are friendlier and part of the bacterial community in a healthy intestine.
Previous studies have found that about 20 percent of E. coli strains produce a DNA-damaging toxin called colibactin. People with inflammatory bowel disease and colon cancer often have high levels of these strains in their digestive systems.
In order to discover what colibactin does to our body, Emily Balskus of Harvard University in Massachusetts and her colleagues injected E. coli, which produces colibactin, into the cells of the human intestine.
They found that the toxin severely damaged the DNA of the cells after 16 minutes. The cells injected with non-colibactin-producing E. coli did not undergo such changes.
When the team repeated the experiment in mice, they found the same result in their colon cells. "This is the first time we see evidence that colibactin directly damages DNA in cells and mice," says Balskus.
They have not yet investigated whether this damage will become cancerous, "but in other settings, such as tobacco products, there is good evidence that [DNA destruction] is carcinogenic," says Balskus.
It is not known when or why some E. coli produce colibactin. Many people have E. coli capable of producing colibactin in the intestine, but they appear to be completely healthy. "We do not know what that means," says Balskus.