New studies have discovered how oral bacteria disrupts the gut microbiome
Oral Bacteria? As if you don’t have enough reasons to feel guilty for avoiding the dentist, it turns out a healthy mouth is linked to a lot more than the absence of cavities and plaque. Researchers say our mouths are home to billions of bacteria with influence far beyond our teeth and gums. It’s an influence they are just starting to understand.
“We know oral bacteria affect almost every aspect of our health—metabolism, cardiovascular system, neurological health, and more,” says Yiping Han, a microbiologist at Columbia University Dental and Medical Schools in New York City.
Scientists like Han are grappling with questions that will change our understanding of how the body works. They’re studying the ways bacteria in our mouths interact with one another. They’re also investigating why mouth bacteria show up in other parts of the body, such as the lining of the heart, around tumors, and even in the brain.
The idea that our bodies host a world of bacteria may sound familiar. We’ve seen a surge of scientific research on the gut microbiome, which describes the bacteria living in the gastrointestinal tract. Gut bacteria seem to have a hand in a surprising number of functions, from the predictable (like digestion and nutrient uptake) to the more surprising (obesity and depression). So it makes sense that the next place for a breakthrough would be upstream—the mouth.
Scientists have identified 700-plus strains of bacteria swiped from cheeks around the world, which makes the mouth the second-largest microbiome in the body (just behind the GI tract). And they’re trying to figure out the roles of these strains. Sussing out what combination of bacteria makes a person healthy or sick would be a major step in staving off diseases.
For instance, certain bacteria are the culprits behind a bunch of maladies that send you to the dentist, like plaque, gum disease, and bad breath. Those kinds of discoveries get dentists excited. That said, what’s really interesting is that oral bacteria pop up all over the body and are linked to a host of other medical issues.
This newfound knowledge is made possible by advancements in DNA and RNA decoding, and microscopic imaging. Scientists upload new information to oral microbiome repositories at the Forsyth Institute in Cambridge, Massachusetts; Ohio State University; and Los Alamos National Laboratory in New Mexico.
This knowledge sharing has helped to unravel some long-standing medical mysteries. For instance, doctors have, for decades, puzzled over why people with cardiovascular issues, like endocarditis (an infection of the lining of the heart) or clogged arteries, also have gum disease. It turns out that the inflamed gums allow oral bacteria to get into the bloodstream. This is where they can wreak havoc on the heart and vessels.
That’s not the only way that bacteria in the mouth end up elsewhere. Swallowing a teaspoon of saliva disperses 5 million bacteria into your digestive tract, says Colleen Cavanaugh, a biology researcher at Harvard University. (Preliminary findings suggest that oral sex can be a conduit, too, Han says.)
“It’s a mobile microbiome,” Han says. “There are some bacteria that, when they’re in the mouth, they’re mostly harmless, but when they go to other sites in the body, they become pathogens,” Han says.
Take Fusobacterium nucleatum, or Fn for short. In your mouth, it causes dental plaque. But it’s a menace if it encounters a colon cancer tumor. Han’s lab has found that Fn acts as an accelerant, prompting a tumor to grow faster, protecting it from chemotherapy drugs, and encouraging it to metastasize to the liver (which is particularly dangerous). Fn has also been found in the joint fluid in people with rheumatoid arthritis, an inflammatory disease. It’s even been detected in brain abscesses, meaning it has the ability to jump the blood-brain barrier. This is uncommon because very few substances that float in the blood can get to the brain and spinal cord.
Does Fn cause colon cancer? No. But down the road, knowing that a patient’s tumor is being bodyguarded by Fn may change the way he’s cared for. – Eric Chow
And new research suggests that the oral bacteria can also have a direct impact on how cancer plays out. A study published in Scientific Reports found that people who are diagnosed with oral or throat cancers—which are notoriously difficult to treat and have high rates of mortality—had similar oral microbiome compositions.
There are a couple of explanations for why people with the same disease would share similar bacteria. Bad habits like drinking, smoking, and poor oral hygiene create the perfect conditions for certain bacteria to grow (and others to die off). Genetics probably play a role, in that a person’s mouth is predisposed to having more of some bacteria, less of others. Most likely, it’s a little bit of both. Regardless, knowing how the microbiome changes composition when it’s sick may help doctors prevent and treat disease.
Scientists are interested not only in the bacteria they find but also in what they don’t. A study from the University of Copenhagen finds not enough bacteria called Lactobacillus can be a predictor of weight gain. We’re not at the place that simply peppering a person’s mouth with some Lactobacillus would get people to drop pounds. But that could be where things are headed.
Bacteria also interact with one another. It’s an ecosystem, after all. Decoding these relationships could be the beginning of a new way to treat oral issues, says Ted Jin. He’s the founder of Qii, which makes a canned tea drink designed to encourage balanced mouth bacteria. The beverage is more anti-plaque than anti-cancer, but it’s part of a larger effort by Jin and his team of researchers to understand the intricacies of the mouth biome in order to make better oral-care products down the road. (Imagine: a world without fillings.)
What experts are learning about the state of our maws isn’t entirely rosy. For one, there’s a hypothesis that the mouths of people in the U.S. aren’t as diverse as they should be. Crappy, overly processed diets with too much sugar and not enough fresh produce are not great for a healthy oral ecosystem. Nor is our fascination with all things antibacterial. Experts are beginning to discourage patients from using harsh mouthwashes that kill good and bad bacteria indiscriminately. (The Food and Drug Administration banned certain ingredients in antibacterial hand soap in 2016, in part because they were killing off good bacterial strains and promoting “superbugs.”)
These differences may also help explain why there are areas of the world with less-advanced oral hygiene practices. But where people generally have teeth and gums that are just fine. And in addition to geography and diet, there’s certainly a genetic component to all of this. So if your kid’s got a mouthful of cavities, you’re at least partially to blame.
Another upshot to all of this will come in the form of precision medicine. Soon you may be able to send off some spit and receive back a mouthwash tailored specifically for your oral microbiome, Jin says. If you have too much of a certain bacteria strain, you could swish with a formula that contains another. This would act like a microscopic smart bomb to get conditions like halitosis (bad breath) or gum disease under control.
You don’t have to wait for the mouthwash of the future to do right by your mouth. For starters, eat a Mediterranean diet, says Jason Tetro, a visiting scientist at the University of Guelph in Ontario and author of The Germ Code. “Staples of the diet, such as fish and vegetables, have omega fatty acids and phytochemicals,” Tetro says. “And in some cases, things like pomegranates have antimicrobials, which seek out and kill bad bacteria and help maintain a less acidic environment.”
His secret weapon against oral inflammation? The sesame paste tahini. It helps promote an alkaline environment in the mouth, Tetro says. If your maw feels a little sore from fast food or booze? Swish with a spoonful of tahini for some low-tech relief.
And low-tech is kind of the point. While researchers like Han are teasing out microscopic secrets, one petri dish at a time, what we’re learning seems to substantiate what we already know. Brushing and flossing is still a great way to keep your oral microbiome healthy. And no more excuses: time to schedule that dentist appointment.
By Marjorie Korn
