WASHINGTON, Feb. 1 (Xinhua) -- Scientists said Thursday they have identified two types of bacteria that collaborate to increase the risk of colon cancer.

A series of experiments in mice suggested that the combination of Escherichia coli and Bacteroides fragilis (ETBF) promote inflammation and break down the protective mucus layer of the colon, according to the study published in the U.S. journal Science.

The findings suggested new ways to more effectively prevent colon cancer, a disease that kills more than 50,000 people each year in the U.S. and is on the rise among younger adults aged 20 to 50.

In the study, a team led by researchers at the Johns Hopkins Bloomberg-Kimmel Institute for Cancer Immunotherapy began by analyzing tissue samples from patients with a genetic condition associated with increased risk of developing precancerous polyps in the colon, called familial adenomatous polyposis (FAP).

Unlike samples from patients with sporadic polyps, FAP samples contained patches of bacteria in which E. Coli and ETBF were particularly prevalent, a result confirmed through a bigger dataset of samples from FAP patients.

Intriguingly, E.coli and ETBF express genes associated with increased DNA damage and tumorigenesis, respectively.

When the researchers implanted these bacteria from FAP patients into mice, they found that mice with only one species developed few tumors, whereas mice that were colonized with both bacterial species were substantially more prone to invasive cancer and death.

Through a series of experiments, they found that these bacteria invade the protective mucus layer of the colon and collude to create a microenvironment that induces chronic inflammation and subsequent DNA damage that supports tumor formation.

"It is the combination of these effects, requiring coexistence of these two bacteria, that creates the 'perfect storm' to drive colon cancer development," said Professor Cynthia Sears of the Johns Hopkins Bloomberg-Kimmel Institute for Cancer Immunotherapy, who led the study.

Both types of bacterium are found to commonly colonize young children worldwide, potentially contributing to the rise in colon cancer rates among younger people.

It may be possible to prevent this disease by keeping the colon from becoming colonized by these two problematic bacteria, or by devising drugs or vaccines that target their toxins, Sears added.