A common type of bacteria found in the mouth can travel to the colon and speed the growth of malignant tumors, according to new research.

Researchers at Fred Hutchinson Cancer Center in Seattle examined colorectal cancer tumors from 200 patients, measuring the levels of a specific type of bacteria known as Fusobacterium nucleatum, which previous research has shown to infect tumors.

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In the new study, published in the journal Nature, researchers found that the oral bacteria has different subtypes – and one in particular, Fna C2, was elevated in tumor tissue compared with healthy tissue. Fna C2 was also present in higher numbers within stool samples of patients with colon cancer compared with those of healthy people.

“We’ve consistently seen that patients with colorectal tumors containing Fusobacterium nucleatum have poor survival and poorer prognosis compared with patients without the microbe,” Susan Bullman, a cancer microbiome researcher and co-corresponding study author, said in a release. “Now we’re finding that a specific subtype of this microbe is responsible for tumor growth. It suggests therapeutics and screening that target this subgroup within the microbiota would help people who are at a higher risk for more aggressive colorectal cancer.”

These findings are particularly significant since colorectal cancer has been rising among people 55 and younger by 1% to 2% each year since the mid-1990s, according to a recent report from the American Cancer Society. Although the overall rate of colorectal cancer has been declining, it is now the leading cause of cancer death among men under 50 and second among women in the same age range.

Colorectal cancer kills more than 52,000 Americans a year, according to the American Cancer Society.

“We have pinpointed the exact bacterial lineage that is associated with colorectal cancer, and that knowledge is critical for developing effective preventive and treatment methods,” said Christopher D. Johnston, co-corresponding author and molecular microbiologist.

Researchers found that the Fna C2 subtype had “acquired distinct genetic traits suggesting it could travel from the mouth through the stomach, withstand stomach acid and then grow in the lower gastrointestinal tract.”

The discoveries in this study may lead to further research into developing microbial cellular therapies, using modified versions of bacterial strains to deliver treatments directly into tumors.