The human gut is home to billions of bacteria responsible for our physical and mental health. But according to a new studypublished in the magazine Science on October 28, 2022, the gut microbiome may also harbor other, more harmful bacteria. A common human gut microbe is indeed suspected to play a major role in the development of colorectal cancerthe second deadliest and third most common cancer in the world, with two million diagnosed cases and one million deaths per year.
In men, the risk of developing colorectal cancer is 1 in 23, compared to 1 in 25 in the woman. The main factors are the usual factors: age, smoking, alcohol consumption, obesity or even a diet low in fruits and vegetables and too rich in meats. Having inflammatory bowel disease (IBD) could also increase the risk.
The team of researchers from Yale University, responsible for the study, discovered that certain strains of the bacterium Morganella morganii – a bacterium that proliferates in the intestines of patients with inflammatory bowel disease – produced cells toxic to human DNA. “We found that various gut microbes exhibited DNA-damaging activities, suggesting that microbiota-mediated genotoxicity may be more widespread than previously thought.”said Noah Palm, co-author of the study.
Genotoxins at risk for DNA
The researchers analyzed bacteria from patients with inflammatory bowel disease, another known risk factor for colorectal cancer. After examining more than 100 types of gut bacteria from the stools of 11 at-risk patients, they identified 18 strains that damaged the gene molecule across three unique species.
After having focused their analyzes on the family of genotoxins produced by Morganella morganiicalled the indolimines, researchers found that they exacerbated cancer in mice with colorectal tumors. However, this effect was eliminated when the researchers stopped the bacteria from producing indomine.
This is not the first time that a research team has demonstrated the link between bacteria in the digestive system and genetic mutations causing cancer. In February 2020, Professor Cayetano Pleguezuelos’ team discovered that a specific strain of E.coli produced a toxic molecule called colibactin which also damaged the DNA of human cells.
The researchers hope that “identification of dangerous genotoxins could improve colorectal cancer diagnosis and therapies in the future”. Indeed, this discovery could help create screening tools and lead to preventive treatments that reduce the abundance of cancer-linked bacteria in patients’ intestines and thus reduce their risk of disease.
Sources:
- Commensal microbiota from patients with inflammatory bowel disease produce genotoxic metabolites, ScienceOctober 28, 2022
- Gut check: Health-promoting microbiome also harbors harmful bacteria, Yale NewsOctober 27, 2022
