Some intestinal diseases , including colorectal cancer, could be caused by bacteria . To reach these conclusions are two recent scientific studies, published respectively by Nature and Cell Host & Microbe . 

The triggering causes of colorectal cancer

In Western countries, bowel cancer (which can occur in the colon or rectum, more rarely in the small intestine) is the second largest malignant tumor in the female population (after breast cancer) and the third in the male population ( after that to the lung and prostate ). In recent years , the mortality rate has dropped , mainly thanks to screening programs and increasingly personalized treatments. As stated on the website of the Humanitas Gavazzeni hospital , it can be due to several causes :

• it can be the result of chronic inflammatory diseases, such as ulcerative colitis or Crohn’s disease ;
• in 25% of cases it is attributable to a strong family predisposition ;
• in most cases, however, it is not possible to identify with certainty the triggers .

Maintaining a correct and balanced lifestyle is important in terms of prevention . In particular, it has been shown that the onset of this type of cancer is lower for those who follow a low-fat diet with a high intake of fiber . Smoking is also considered by the Airc as a risk factor. 

Escherichia coli under the lens of scientists

This is the framework on which the scientific community is already largely in agreement. The two new studies add further elements, which are sure to deserve further study in the future. 

As the New Scientist magazine , which reports the news, explains, the researchers noted that a specific variety of Escherichia coli (a common intestinal bacterium) is particularly common in the feces of people who have had colon cancer. 

It is not yet clear, however, whether it is the bacterium that triggers the tumor ; the alternative hypothesis is that it is able to proliferate more easily in the intestine of those who have already developed the disease.   

A bacterium that causes DNA mutations

To investigate the matter, the authors of the paper published by Nature injected the bacterium into human intestinal cells , causing them to develop in the laboratory for five months. So they found that the microorganism triggers mutations in two of the four DNA bases (adenine, cytosine, guanine and thymine). 

After that, they went to plumb two previous studies in which the genes of around 6,000 people with cancer had been sequenced . The gut bacterium-induced abnormality has been found in 5 to 10 percent of people with colorectal cancer. Conversely, it was practically absent from the other cases. 

“I wouldn’t say it’s the deciding factor, but it takes us a step further,” said Cynthia Sears , a researcher at Johns Hopkins University. If the results were confirmed, in fact, it would be possible to take antibiotics to defeat the “bad” bacterium and probiotics to develop the “good” variant that keeps it away. 

The study published by Cell Host & Microbe instead shows that the lack of certain bacteria can favor the onset of ulcerative colitis , which leads the immune system to “attack” the intestine. From this evidence, new clinical trials have been started: the first, on animals , supported the thesis; the second, on humans , will be completed next year.