Oral Bacteria: It Ain’t All Bad

Betty Zou, Ph D.

You think you’re practicing good oral hygiene—you floss every night, brush your teeth after each meal and go for regular checkups at your dentist—but even so, your mouth is teeming with billions of bacteria. They’re on every surface and hidden in every nook and cranny. Before you go running for the antibacterial mouthwash, consider this: most of those bacteria are either harmless or good for you.

That might be hard to believe given bacteria’s image problem. For centuries, they have been blamed—rightly so—for illnesses that have wiped out entire cities and wreaked havoc people’s lives. These days, though, you are as likely to hear about the “good” bacteria keeping you healthy as you are about the disease-causing bad guys.

The bacteria in your mouth are no exception. Conversations about oral health are all too often dominated by warnings about nasty microbes lurking around to cause cavities and gum disease. Less talked about, but equally worthy of mention, are the legions of beneficial bacteria that work behind the lips to keep your oral ecosystem balanced and your mouth healthy.

How do they love teeth? Let us count the ways.

First of all, their mere presence can help to keep harmful bacteria out, a phenomenon called colonization resistance. When a new bacterial pathogen arrives in the mouth, it has to first compete against established communities of native bacteria for food and habitat. In most cases, the newcomer is crowded and kicked out before it has a chance to harm the host.

In addition to this passive form of protection, some native oral bacteria can actively resist a hostile takeover. For example Lactobacillus bacteria are among the most frequently found members of the oral microbiome, the complex community of microorganisms that reside in the mouth. A 2011 study tested 10 different species of oral Lactobacillus bacteria and found that most were able to block the growth of pathogens like Streptococcus mutans and Porphyromonas gingivalis that are known to cause cavities and gum infections, respectively. They do this by producing lactic acid which lowers the pH and makes the environment inhospitable for the bad bacteria and by making toxins that attack their cell walls.

In a 2007 study, Swedish researchers collected Lactobacillus bacteria from two groups of people—those who had no history of cavities and those with cavities. While all the harvested Lactobacillus had some degree of antimicrobial powers, those from the cavity-free individuals were the most effective at killing the cavity-causing bacteria Streptococcus mutans. Perhaps not surprisingly, people in the cavity-free group also had the lowest number of S. mutans in their oral microbiomes.

Another way in which beneficial mouth microbes help maintain oral—and overall—health is by fine-tuning the immune system. Streptococcus salivarius is one of the first bacteria to colonize the mouth after birth and remains a dominant member of the oral microbiome throughout a person’s lifetime. Studies have shown that it can turn down the immune response, which is important given that many oral conditions are driven by inflammation.  

In addition to its anti-inflammatory properties, Streptococcus salivariusproduces toxins that target two of its Streptococcus family cousins S. pyogenes and S. pneumoniae, the leading causes of strep throat and pneumonia, respectively. A 2012 study by Japanese researchers showed that S. salivarius could also protect against oral thrush caused by the fungus Candida albicans although how the bacteria achieves this is unknown.

With all their beneficial effects, Streptococcus salivariusand some types of oral Lactobacillus bacteria are being developed as probiotics to help consumers achieve and maintain a balanced oral microbiome. It isn’t far-fetched to think that in the future, instead of reaching for that antibacterial mouthwash, you may simply take a swig of a bacteria-infused beverage to keep cavities and gum disease at bay. Bottoms up!

Betty Zou, Ph D.

Scientist turned science writer and communicator. I turn complex scientific concepts and studies into clear and engaging content for diverse lay audiences. Previous work include blog posts, news articles and releases, patient and customer profiles, feature length stories, donor reports and marketing materials. My areas of expertise are molecular biology, microbiology and microbiome-related topics but I have also written extensively about other health and medicine topics such as cancer, cardiology and trauma.


Much more than just slobbery puppy kisses, saliva has tooth-protecting and microbe-busting properties that make it absolutely drool-worthy.


Much more than just slobbery puppy kisses, saliva has tooth-protecting and microbe-busting properties that make it absolutely drool-worthy.

The mouth harbors one of the most diverse bacterial ecosystems in the body. We’re focused on understanding both the harmful bacteria that trigger cavities, periodontal disease and bad breath as well as the beneficial microbes that support oral health. We’re finding ways to wipe out the bad while nurturing the good. qii is different. With a shelf-stable pH around 7, it helps maintain a neutral, non-acidic oral environment that allows the beneficial bacteria in your mouth to thrive.