Gut Bacteria Can Cause Colon Cancer

The bacterium that is part of normal, healthy gut flora can also inflict the biggest damage. E. coli, the resident gut bacteria, can trigger genetic mutation in human DNA and result in colon cancer in one out of 10 cases, reports a new study published in the Nature.

Genetic mutation is one of the most common causes of colon cancer but recently suspicions have arisen that E. coli, one of the 30-40 bacterial species living in the gut, can produce a toxin that can damage DNA and prompt colon cancer in the host.

There are over 100,000 new cases of colon cancer in the US each year. It happens more in men than women. It is the second leading cause of cancer death in the country, with lung cancer being the first. It is prevalent in older adults, usually 50 or above, but recent evidence shows that people as young as 20-29 can also be the possible target. Doctors do not know the exact cause but suspect an unhealthy diet, obesity and smoking as possible gut wreckers.

Or perhaps they are genetically susceptible to the disease, as researchers including Professor Hans Clever of the Hubert Institute found out. He believes a specific strain of E. coli, called pks+ E. coli, is the main culprit in a minority of bowel cancer patients.

pks+ E. coli strain is commonly found in the feces of colon cancer patients. However, it is yet unclear if it actually causes cancer or just increases in number in the gut of cancer patients. pks+ bacterium has a specific set of enzymes that synthesize colibactin, the toxin that damages the cells in the gut, interferes with the DNA sequence and turns them cancerous in about five out of 100 bowel cancer patients.

The research teams, from the UK, US and the Netherlands, grew tiny replicas of human gut,  called organoids, in the laboratory and injected them with the bacteria (pks+ E. coli and another species called isogenic-pks-mutant bacteria) over five months to see the effects of the toxin on healthy cells. As suspected, the pks+ microbe inflicted damage on the DNA by changing the sequence of four nucleotide letters. This led to a double-strand breakage of the DNA. The damage was absent from the other set of organoids injected with isogenic species.

The scientists performed whole-genome sequencing of the organoids before and after the experiment and compared the results with the cancer genomes of 5,876 people and found stark similarities. As many as 5-10% of colon cancer patients from two cohorts of earlier studies had similar genetic mutations.

Dr. Ammar Malik, a Ph.D. scholar, says:

Medically speaking, this is very strong evidence. “If the results are confirmed, antibiotics can help the patients suffering from cancer-causing bacteria.

Bowel-Cancer Screening – Red Flag Symptoms

The US Preventive Services Task Force (USPSTF) recommends that all adults age 50 and above should go for annual screening for colorectal cancer (CRC). CRC screening can be done with the help of a fecal occult blood test (FOBT), sigmoidoscopy and colonoscopy.

However, given the sharp incline in CRC among the young population, experts believe the screening should be started earlier. Dr. Ammar advises watching out for “CRC red flag” symptoms (bleeding, sudden weight loss and changes in bowel habit) and seeking immediate medical help.

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