How Gut Bacteria Contribute to Colon Cancer Development

There are several risk factors, which are associated with colon cancer. Among these are obesity, age and others. Until recently, there were saboteurs participating in tumor development which remained anonymous. A duo of gut bacteria species, a recent research suggests, can drive colon cancer – the discovery can help identify those who may benefit from regular screening.

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Known risk factors

Just like any other type of cancer, colorectal cancer is linked to a set of risk factors. Many of them are shared with other diseases, and some of them are even preventable.

Among the risk factors for colorectal cancer are obesity, the rates of which have quadrupled, following a diet rich in processed meat, red meat, meat cooked at high temperatures and other kinds of unhealthy food, physical inactivity, smoking, and alcohol use – these are the things you can change quite easily. As to other risk factors, which include age, gene mutations and a family history of certain colorectal diseases, one should be aware of their ability to increase the risk of developing cancer of this type and may prefer to undergo health exams more often.

However, it appears that the range of risk factors is not limited to the list mentioned above. Gut bacteria, which are called the human microbiome, include both good (called probiotic bacteria) and bad (called pathogenic bacteria) species. A recent research suggests that two bacteria species can contribute to cancer development, thus opening new ways for possible prevention.

A wicked duo

A team from the John Hopkins University has discovered that certain bacteria are capable of inducing colorectal cancer or helping precancerous cells turn into tumors faster. The two species in question are Bacteroides fragilis, which are normally part of the human colon microbiome but can cause infection if they get into the bloodstream or tissues, and a certain strain of Escherichia coli expressing colibactin.

The colon lining is a mucus shield which protects the organ and prevents invaders from getting into the tissue. The investigators found that these two species can pierce this layer and form a thin film as they grow, which results in having the lining covered with bacteria. Both microbes affect the gut by releasing toxins which cause inflammation and damage the affected cells’ DNA, thus driving cells faster toward cancer. The researchers conducted an experiment which showed that the toxins produced damage DNA when epithelial cells are exposed to them in Petri dishes. The same effect was seen in mice: tumors appeared in the rodents’ colons when the invaders were put into them.

In order to reveal whether the microbes can cause cancer in humans, the scientists examined the samples of six colons which were removed from patients with a genetic condition, which is rare but often deadly, called familial adenomatous polyposis, often abbreviated as F.A.P. The condition leads to development of dozens, if not hundreds, of polyps, which cannot be removed due to their number. In those without the condition, polyps are usually removed in the course of getting a colonoscopy. Most polyps remain harmless and do not progress, but as they are so numerous in patients with F.A.P., the condition almost inevitably results in cancer.

When the scientists analyzed 25 samples with tumors, they saw the same biofilm made up of E. coli and B. fragilis. However, in tissues from healthy patients, only several samples had the duo. They also found that neither of the two can induce cancer without the help of the other, as another mouse experiment showed.

What does it mean for medicine?

Although the results of the study do not suggest that everyone whose body harbors both species is likely to develop colon cancer, the researchers believe it can be a major risk factor. They suppose that if further research proves the role of these bacteria is crucial, they will be able to develop a drug or vaccine to help those infected with both microbes. It remains unclear whether the bacteria combo drives colon cancer in patients other than those with F.A.P., i.e. in the general population. However, simply eliminating the bacteria is not a very good option, as many other species, which are good bacteria, will die too.

That is why the researchers recommend that those who have both species in their gut undergo regular screening.

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