Mouth Microbes

The Helpful and the Harmful

Illustration of a community of microbes

Do you know what’s in your mouth? It’s home to about 700 species of microbes. These include germs like bacteria, fungus, and more.

“Everybody has these microbes in their mouth,” says Dr. Robert Palmer, an NIH expert on oral microbes.

Some microbes are helpful. Others can cause problems like tooth decay and gum disease. Troubles begin when microbes form a sticky, colorless film called plaque on your teeth.

Brushing and flossing help to keep your mouth clean. But after you brush and floss, germs grow again and more plaque forms. That’s why you need to clean your mouth regularly.

Community Growth

Different microbes grow in different places. Some stick to your teeth. Others prefer your tongue. Some lurk in the tiny pockets between tooth and gum. Once they’ve found their homes, they form diverse communities with the other germs.

Mouth microbes work together to protect themselves with a slimy, sticky material called a matrix. The matrix in plaque makes it harder to remove it.

The communities within the matrix include both helpful and disease-causing microbes. The good microbes help keep the growth of bad microbes in check. Good microbes also help you digest food and can protect against harmful microbes in food.

Certain things you may be doing can help bad microbes grow better than the good ones. Sugary foods and drinks feed some microbes and help them increase in number and spread out.
Some of these sugar-loving microbes can turn sugar into matrix and acid. The acid destroys the surface of your teeth. The more sugar in your diet, the more fuel is available for these microbes to build up plaque and damage teeth.

“It’s more productive to think about the community than it is to think about the single microbe that causes disease,” Palmer explains.

You can’t stop tooth decay by getting rid of just one type of acid-making microbe. There are several different types of microbes in the plaque that make acid. The good news is that limiting sweets and brushing and flossing regularly can help prevent bad microbes from growing out of control.

Helpful Neighbors

“Many bacteria in our mouths depend on help from other members of their community to survive and prosper,” says Dr. Floyd Dewhirst, a dental expert who studies microbes at the Forsyth Institute.

Because microbes grow in communities, it’s important to understand how both helpful and harmful microbes work. Dewhirst’s team is trying to identify all the different germs living in the mouth and what they do.

Before the team can study a microbe, they have to figure out how to grow it. The challenge is that some microbes don’t like to grow anywhere but in your mouth. About 30% of the 700 species haven’t been grown in the lab yet.

Dewhirst’s team is working on growing those microbes in the lab that no one has grown before. They’re using genetic and other information to identify each one and learn more about them.
“The question is,” he says, “once you know who is there and have a quick way of identifying them, what are all of these bacteria doing?”

Dewhirst’s studies have shown that some microbes make certain substances that help their neighbors grow. His team is trying to identify what those substances are.
They also want to find out how these microbes may affect people’s health. Being able to grow microbes in the lab lets scientists run tests to figure out how they’re involved in health and disease. This information could one day help scientists come up with better ways of preventing and treating oral diseases.

Partners in Decay

An important health problem caused by mouth microbes is early childhood tooth decay. “In the U.S., about 23% of our children between the ages of 1 and 5 are affected by this disease,” says Dr. Hyun (Michel) Koo, a dental researcher and oral health expert at the University of Pennsylvania.
Tooth decay can get worse very fast. The microbe matrix and acid from bacteria are thought to be the main cause of tooth decay in young kids.

Koo’s team has found that there’s also fungus in the plaque of kids with rampant tooth decay. The fungus partners with the matrix- and acid-making bacteria to worsen tooth decay.

“Bacteria by itself can cause tooth decay,” Koo explains. “But when fungus is there, it boosts up the entire machinery.”

Koo’s team has shown that some fungus can get energy from sugar that bacteria release while making acid. The fungus then releases substances that feed the bacteria’s growth. This helps the bacteria form an even tougher matrix and make more acid.

Busting Plaque

Koo’s team is looking for new ways to fight plaque buildup and tooth decay. They’ve developed tiny substances, called nanoparticles, that are small enough to get inside and destroy the matrix that protects microbes. The nanoparticles can also kill the acid-making bacteria without harming good bacteria in the mouth.

Koo’s team has shown that these tiny substances can reduce acid damage to the tooth surface. The researchers hope to test the approach in people in the future.

Nanoparticles are just one approach now being studied to prevent or treat mouth diseases. Future technologies may help keep our mouths healthier. You can’t have a healthy body without a healthy mouth.

Related Links


Raizada MK, Joe B, Bryan NS, Chang EB, Dewhirst FE, Borisy GG, Galis ZS, Henderson W, Jose PA, Ketchum CJ, Lampe JW, Pepine CJ, Pluznick JL, Raj D, Seals DR, Gioscia-Ryan RA, Tang WHW, Oh YS. Report of the National Heart, Lung, and Blood Institute Working Group on the Role of Microbiota in Blood Pressure Regulation: Current Status and Future Directions. Hypertension. 2017 Jul 31. pii: HYPERTENSIONAHA.117.09699. doi: 10.1161/HYPERTENSIONAHA.117.09699. [Epub ahead of print] Review. No abstract available. PMID: 28760940.

Liu Y, Naha PC, Hwang G, Kim D, Huang Y, Simon-Soro A, Jung HI, Ren Z, Li Y, Gubara S, Alawi F, Zero D, Hara AT, Cormode DP, Koo H. Topical ferumoxytol nanoparticles disrupt biofilms and prevent tooth decay in vivo via intrinsic catalytic activity. Nat Commun. 2018 Jul 31;9(1):2920. doi: 10.1038/s41467-018-05342-x. PMID: 30065293.

Koo H, Andes DR, Krysan DJ. Candida-streptococcal interactions in biofilm-associated oral diseases. PLoS Pathog. 2018 Dec 13;14(12):e1007342. doi: 10.1371/journal.ppat.1007342. eCollection 2018 Dec. PMID: 30543717.

Funding: NIH’s National Institute of Dental and Craniofacial Research (NIDCR); National Heart, Lung, and Blood Institute (NHLBI); National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK).

Adapted from an article in NIH News in Health, May 2019.

Last Reviewed
June 2019

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