Oral Health is Health

Dental health care and medical health care have been separated for as long as anyone can remember, but that does not stop your body from acting as a whole. Or stop your oral bacteria from influencing the health of organs far removed from your mouth.

When Columbia microbiologist Yiping Han, PhD, first discovered in the 1990s how bacteria from the mouth get to other parts of the body, “people thought it was impossible,” says Han, professor of microbial sciences at the College of Dental Medicine. “But we found oral bacteria are frequently detected at extra-oral sites where there are infections and inflammation.”

We asked her to explain the link and how it works.

The microbes in our mouths

Microbes play a very important part in health and disease. Count the cells in our body and 90% are microbes and only 10% are our cells.

The most complex microbiome in the body is the gut where most of our body’s bacteria live, help us digest food, and fortify our immune system. The second most complex body part is the mouth. About 700 different bacteria species have been identified. Good beneficial bacteria prevent the growth and colonization of bad infection-causing bacteria known as pathogens. 

Your body’s microbiome develops early in life but can change in response to medication, diet, and the environment. When you kiss someone, you transfer bacteria, sharing microbiomes. Families typically have significantly similar microbiomes, mostly because of bacteria swapping but also because of shared genes that influence the microbial community. But there are individual differences.

The “hot” bug

When I first joined the dental school more than two decades ago, I was considering the many bacteria in the mouth and identified Fusobacterium nucleatum as something that might contribute to disease.

It can adhere to and invade into host cells. This fact made me think it must be doing something to us, which made me want to study it.

At that time people told me, "Nobody cares about Fusobacteria; you will never get NIH funding." 

There were very few labs in the world studying it back then, so there were no genetic, animal, or other tools for studying. Over the years my lab gradually built all the tools we needed for the study. And as our work accumulates and more and more labs validate our work, bringing attention to it, it’s now becoming a hot bug because we discovered that Fusobacteria contribute to numerous chronic and acute diseases, like colon cancer and reproductive infection.

Mobile microbiome: How oral bacteria get to places outside the mouth

We found that oral bacteria can translocate (move) to the uterus, colonize (settle in), and elicit inflammatory responses that cause preterm births, stillbirths, and neonatal sepsis. We call it the mobile microbiome.  

Our research showed that oral bacteria can get into the blood circulation, colonize specifically in the placenta and proliferate very quickly, and cause preterm births and stillbirths.

We recently published our findings that significant levels of oral bacteria in the cord blood are associated with early preterm births--babies born before 32 weeks of gestation. And these are actually the most medically relevant cases because early preterm babies have the highest mortality and morbidity.  

Similarly, oral bacteria can translocate to the gastrointestinal tract and contribute to intestinal inflammation. By moving, oral bacteria can create infection and inflammation outside of the mouth.

We’re now studying whether this bacterium could be linked to neurodegenerative diseases like Alzheimer's, autism, or Parkinson's.

If this bacterium is ubiquitous in the oral cavity and everybody has it, why isn’t everybody delivering premature babies and having colorectal cancer?

Not all Fusobacteria can translocate down the GI tract.

We did a study in collaboration with Columbia's GI division. Stomach acid plays a very important role in limiting bacterial translocation. We found that Fusobacteria actually can undergo dramatic biochemical structural change and become coated with amyloids (a protein that builds up in organs), like the plaque you find in the brain of Alzheimer's patients. These amyloids are sturdy and resistant to acid. They act like a shield, coating the bacteria, making the bacteria resistant to acid. They also allow bacteria to colonize in different body sites and stimulate cancer growth.

We think this is how Fusobacteria can translocate down the GI track. We published a paper last year that showed the antibody levels against this amyloid are significantly elevated in cancer patients in both early and late stages. So it could be a way to detect colon cancer early.  

We have identified a novel cancer growth factor that responds to this bacterium. We’re now trying to develop a therapy to target it. This is something that's very gratifying for me: using bacteria as bait to fish out novel biomarkers in cancer.