Scientists have identified a combination of bacteria that appears to increase the risk of colon cancer, a finding that could lead to new ways to more effectively screen for and ultimately prevent colon cancer.
Through a series of experiments, the researchers were able to pinpoint ways in which the two species of bacteria — Bacteroides fragilis and Escherichia coli — promote inflammation and break down the mucus layer of the colon.
“It is the combination of these effects, requiring coexistence of these two bacteria, that creates the ‘perfect storm’ to drive colon cancer development,” said Cynthia Sears, Professor, at the Johns Hopkins Bloomberg School of Public Health.
Both types of bacterium are found to commonly colonise young children worldwide, potentially contributing to the rise in colon cancer rates among younger people.
The findings, published in the journal Cell Host & Microbe and Science, describe a process in which these bacteria invade the protective mucus layer of the colon and collude to create a microenvironment — complete with nutrients and everything the bacteria needs to survive — that induces chronic inflammation and subsequent DNA damage that supports tumour formation.
Unlike most bacteria, which do not make it past the colon’s protective mucus layer, these communities of bacteria that invade the mucus, form a sticky biofilm right next to the colon epithelial cells that line the colon, where colon cancer usually originates.
To investigate the relationship between the bacteria-caused biofilms and cancer formation, the team examined colon tissue removed from FAP patients.
The results showed that the B. fragilis strain was a subtype, called ETBF, which makes a toxin that triggers certain oncogenic, or cancer-promoting, pathways in colon epithelial cells and causes colon inflammation.
The E. coli strain produced a substance called colibactin (synthesized by a set of genes in the bacterial genome called the PKS island), which causes DNA mutations.
In addition, when B. fragilis and E. coli were put into mice predisposed to get bowel cancer, they dramatically increased the number of tumours that formed.