January 9, 2015 | 4 minute read

A growing body of evidence indicates that the trillions of bacteria that live in the digestive tract – might play a role in altering cancer risk. Now, a study suggests that how those bacteria are organized and where they are located in the gut might influence the risk of certain colon cancers.

The study, published in The Proceedings of the National Academies of Science, focused on biofilms – communities of bacteria that help bacteria communicate with each other and grow more efficiently.

When bacteria organize into biofilms, they can breach the protective inner layer in the gut and invade the local tissue, promoting inflammation and possibly cancer.

We have an interesting relationship with the bacteria in our gut. Although many of the microbes provide beneficial services, bacteria – both “good” and “bad” – can cause us harm, so we keep them all at arm’s length, so to speak. Normal, healthy tissue in the colon is coated with a two-layered covering of mucus –a mesh-like outer layer and a gel-like inner layer. Whereas the outer layer creates a moist, cozy environment for bacteria, the inner layer is less hospitable: it provides the last line of defense against their invasion.

The authors of this study compared the bacterial communities from three types of tissue removed from patients in the US and in Malaysia: 1) tissue from colon tumors – both malignant tumors and benign adenomas 2) healthy tissue from the colons in the first group, but far away from where the tumors were located; and 3) tissue taken from healthy patients during routine colonoscopies. Biofilms were present in at least half of the tumors overall, and nearly all the tumors located on the right side. Surprisingly, biofilms were found in nearly all of the tissues located far away from the tumors. Most – 87% – of the colonoscopy biopsies from healthy patients were biofilm-free.

Results were similar from both the US and Malaysian patients, despite genetic and dietary differences between the two groups.

When the scientists observed the tumors with an electron microscope, they noticed that the biofilm-associated bacteria had invaded the tumors and made direct contact with the colon cells.

Among the patients with colon tumors, the scientists noted that the number of bacteria in the biofilms didn’t differ between tumor tissue and normal colon tissues; however, the biofilms in the tumors were significantly deeper, indicating the bacteria had penetrated farther into the tumor tissue.

Next, the scientists determined the makeup of the bacterial communities in the biofilms. They discovered that the types of bacteria spanned a wide spectrum from beneficial to neutral to harmful, which parallels the progression of cells from healthy to abnormal to cancerous.

In colon cells where biofilms form, the scientists found fewer of the key proteins that improve the gut’s resistance to invasion. Proteins that promote inflammation and cancer were increased.

Taken together, the authors of the study concluded that when bacteria organize into biofilms, the colon becomes more vulnerable to bacterial invasion, which in turn, creates an environment that supports inflammation and cancer promotion. The results of this study suggest that the risk of developing colon cancer is five times higher if an individual has biofilms in their colon than if they do not.

Although scientists don’t have enough information to make dietary recommendations to prevent biofilm formation, this much is clear: a lifestyle that includes a healthy diet, physical activity, and maintaining a healthy weight is key to cancer prevention. To learn more, read AICR’s tips for reducing your cancer risk.

The work was funded by the National Institutes of Health through Grants and the Mérieux Institute.

Teresa L. Johnson, MSPH, RDN, is a nutrition and health communications consultant with a long-time interest in the role of plant-based diets and cancer prevention. Her work draws on elements of nutritional biochemistry, phytochemistry, toxicology, and epidemiology.