The mouth rinse test involves first rinsing with water than with saline. Researchers say the test could become part of annual dentist check-ups. Andrea Piacquadio / pexels.com

BLACKSBURG, Va. – Our mouths contain a vast array of bacteria. While most of these cells are likely harmless, a new study reveals that one common bacteria can travel from the mouth to other parts of the body, triggering the spread of cancer cells.

The diverse bacterial environment in our mouths is known as the oral microbiome. A specific cell, called Fusobacterium nucleatum, is part of your microbiome and lives under the gums.

While some mouth bacteria reach other parts of the body by traveling through the digestive system, scientists believe F. nucleatum travels through the blood. Researchers say this bacteria can infect many different areas including the brain, liver, and heart. It is also present in high levels in colon tumors.

Tracking down how cancer spreads

Previous studies demonstrate that F. nucleatum directly invades colon tumors. A 2017 study found that when human tumors in the colon containing F. nucleatum are transplanted in mice, cancer cells with the bacteria break off and attach to the liver. Although this demonstrates that F. nucleatum plays a role in spreading cancer cells, scientists didn’t understand how.

To answer this question, researchers at Virginia Tech examined how human cells respond when colon cancer cells contain F. nucleatum. 

The study in Science Signaling finds F. nucleatum does not directly initiate cancer. It also doesn’t release molecules that trigger cancer migration. Instead, the bacteria sticks to and enters cancer cells. This causes cancer cells to release two proteins, IL-8 and CXCL1. These two proteins play a critical role in immune system activation in response to infections.

In addition to their role in the immune system, previous studies find the proteins can cause cancer cells to spread. According to the researchers, their study is the first to find that bacteria causes cancer cells to release IL-8 and CXCL1. The VT team adds IL-8 and CXCL1 can also trigger inflammation, a key characteristic of cancer which can release additional cancer-promoting proteins.

Mouth bacteria unlocks new way to slow cancer?

Researchers say these findings could provide insight into potential therapeutic targets for cancer treatments. Blocking the secretion of cancer-promoting proteins like IL-8 and CXCL1 could help to prevent cancer cells spreading. It may also be a useful alternative to antibiotics. While antibiotics could kill F. nucleatum, doing so can also kill beneficial bacteria.

“We need to know if there are other important bacteria that could be working in synergy with F. nucleatum to drive cancer. We need to understand the physiological role of these bacteria as we can’t just go about clearing them from the body because we need them for some situations. Oftentimes, bacteria are needed for chemotherapy to be fully effective,” says researcher Scott Verbridge in a media release.

“I also think it’s interesting to ask if the bacteria are causing this cellular migration as a way to get around in the human body,” he adds. “There could be a selective advantage for any infectious agent, a virus or bacteria, that could get inside of a host cell and migrate.”

While the study focused on colorectal cancer cells, the research team is also studying other types of cancer including pancreatic cancer, breast cancer, and squamous cell carcinoma of the mouth.

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About Brianna Sleezer

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