Probiotic bacteria may cause bowel cancer, there is no proof they treat gut infections, says study

Findings suggest that doctors might be able to use antibiotics to stop bowel cancer 

Probiotic bacteria may cause bowel cancer, there is no proof they treat gut infections, says study
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A bacterium commonly found in probiotic food could actually be held responsible for causing bowel cancer, suggests a new study.

The finding suggests that doctors might be able to use antibiotics to stop this bacterium from causing bowel cancer — the third most common cancer among Americans. The condition is expected to cause more than 50,000 deaths in the US in 2020.

Nissle E. coli 1917, the bacterium linked to bowel cancer, was present in the intestines of about 10-20% of people covered in the study. "It is the smoking gun, showing that the bacteria has been active in the bowel of those patients," Professor Hans Clevers of the Hubrecht Institute in The Netherlands tells MEA WorldWide (MEAWW). Professor Clevers and his team have authored the study.

Named after its discoverer Alfred Nissle, the probiotic bacterium is believed to help treat gastrointestinal infections and inflammation.

But scientists are not entirely convinced of its benefits. "There is no real objective evidence for the therapeutic effects of Nissle," explains Clevers.

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What is more, the bacteria produce a toxin named colibactin, which is suspected of introducing cancer-causing mutations into the DNA of human cells. So Cayetano Pleguezuelos-Manzano, the first author of the study and his colleagues, set out to learn more.

The team injected the toxin into lab-grown mini versions of the intestines on weekdays for five months. They extracted DNA from these lab-grown organs to scan them for mutations.

The team injected the toxin into lab-grown mini versions of the intestines. Mini organ (green) filled with labeled bacteria (blue). (Cayetano Pleguezuelos-Manzano, Jens Puschhof, Axel Rosendahl Huber, ©Hubrecht Institute)

They found that cells injected with the toxin had twice the damage in the DNA, compared to those that were not injected. Further, all the damaged cells had a particular pattern of mutations. 

With these positive results, the team wanted to check for the same pattern in human cancer cells. So they scanned the DNA of more than 2,000 bowel cancer samples from UK patients.

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The pattern stood out in 4 to 5% of patients. This suggests that colibactin-producing E. coli may contribute to 1 in 20 bowel cancer cases.

“We will be looking at its presence in individuals with and without cancer and whether it helps in bowel cancer screening,” said Philip Quirke, a professor of pathology at Leeds University and a senior researcher on the study, told the Guardian.

The team has more to learn. "We do not know much about the presence of this bacterium in the human population at large. It would be great to hook up with nationwide bowel cancer prevention programs, which collect fecal samples,"  explains Clevers. "It may be of great interest to study how existing antibiotics can be used to eradicate this strain of E. coli in individual carriers," he adds.

As scientists carry out further investigations, Nicola Smith, senior health information manager at Cancer Research UK, has some advice: "not smoking, keeping a healthy weight, eating a diet high in fiber and low in red and processed meat will all help".

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The study has been published in Nature.

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