For several years, researchers have been documenting a clear link between gut microbiome patterns and bowel cancer,media reported. Now, a new study is the first to provide evidence of a direct causal link between the bacteria and cancer development, with researchers discovering that DNA mutations in some colorectal tumors are caused by a strain of gut bacteria.
Intestinal microbiome imbalances have long been observed to be associated with the occurrence of bowel cancer, but researchers have only remained at the hypothetical level. To find out the potential pathogenesis, an international team of researchers began studying an intestinal bacteria known to produce certain toxins.
Previous studies have found that some Strains of E. coli produce a toxin called colibactin. The toxin has previously been shown to cause DNA damage in laboratory cell tests, so new research begins to explore whether it can also be found in intestinal cells and in subsequent colon tumors.
The first step in the study is to use intestinal organs to explore whether colibactin produced by E. coli causes DNA damage. An organism is essentially a tiny replica of the human organ, which can be cultured in the laboratory to study potential treatments for various diseases.
The researchers detected that about five months after exposure to E. coli that produced colibactin, DNA damage in these organelles doubled compared to cells of e. coli strains that did not produce colibactin. The researchers found that because DNA damage caused by colibactin followed very specific patterns, they could study whether these patterns could also be found in cancer tumor samples.
In a subsequent analysis of more than 2,000 bowel cancer samples, the researchers found that in nearly 5 percent of tumors there was colibactin-induced DNA damage. This suggests that toxins produced by gut bacteria play a role in about 1/20 of bowel cancers.
“It is well known that substances such as tobacco or ultraviolet light can cause specific patterns of DNA damage, and these fingerprints can tell us a lot about the potential for cancer in the past,” said Hans Clevers, author of the new study. But this is the first time we’ve seen such a unique pattern of DNA damage in bowel cancer, caused by bacteria that live in our guts. “
Of course, it’s too early to say that this particular mechanism is completely related to some bowel cancers, but the researchers suggest that a method could be developed to detect DNA damage in intestinal cells induced by colibactin, which could help identify those most at risk for bowel cancer.
“Our goal is to find a way to identify and lock in these toxin-carrying bacteria before they do too much harm,” says Philip Quirke, a researcher at the University of Leeds. We may be able to find other toxins to help more people in the future. “
The new study questions the safety of probiotic supplements containing known bacteria that produce colibactin. Although the specific strain of E. coli used in this study is not used as a probiotic, it is a type known as E. Coli nissle’s popular probiotic strain — which produces colibactin.
E. coli nissle has been used safely as a probiotic for a century, but Hans Clevers has called for new clinical studies to evaluate the overall therapeutic effects of these probiotics that produce colibactin.