Contrary to what you might have heard about strep throat or even strep pneumonia, there are some very beneficial Streptococcus bacteria living in your mouth. They’ve been there since you were an infant and they are critical for keeping your mouth healthy. In fact, my favorite oral probiotic species- Streptococcus salivarius– is one of these beneficial bacteria. It should be in everyone’s toolkit. It is backed by strong evidence showing it can ward off pathogens that cause cavities, gum disease, ear infections, tonsil infections, and throat infections. Fewer infections mean fewer antibiotics (hooray!). It can also reduce bad breath and turn off inflammation in the mouth. Too good to be true? It seems so. Keep reading to learn what you can do to promote the healthy Streptococcus species in your oral microbiome- and crowd out the bad. Practitioners and consumers alike need to know about this safe, natural treatment for oral, throat, and ear health.


Are Streptococcus normal oral bacteria?

Streptococcus bacteria are found in almost every location in the human body. They dominate the mouth and the respiratory tract but they don’t stop there. They are in the gut, on the skin, in the vagina, and in the nose. They are considered commensal, or normal, “healthy” bacteria. The majority do no harm to us and they often help us. But there are certain Streptococcus species that can be harmful to us, which I’ll discuss later.

As you might imagine, the genus of Streptococcus bacteria is huge. It is divided into 8 distinct groups. Six of those include oral Streptococcus bacteria (which are the top six listed here).1

  • Streptoccus mitis
  • Streptococcus sanguinis
  • Streptococcus anginosus
  • Streptococcus salivarius
  • Streptococcus downei
  • Streptococcus mutans
  • Streptococcus pyogenic
  • Streptococcus bovis



Streptococcus species are the most abundant bacteria in the mouth. And they are the earliest bacteria to make a home in the mouth. They are high in breastmilk and they make up the majority of an infant’s oral microbiome.2

Streptococcus species are the earliest colonizers of the tooth surface, including Streptococcus mitis, Streptococcus sanguinis, Streptococcus gordonii, and other closely related taxa. They bind to cells that line the mouth and can be found on the gums, tongue, tonsils, and in the saliva. They bind tightly to the naked tooth, where they build up a framework to which other species can bind.3

Some Streptococcus mouth bacteria are known to specifically ward off pathogens such as the gum disease pathogen, Porphyromonas gingivalis.2 Streptococcus mitis and Streptococcus sanguinis species fight off newcomers by producing alkali, bacteriocins, and hydrogen peroxide. Bacteriocins are natural antimicrobial compounds that can kill off other microbes.

Strep species can calm down inflammation in the mouth, promoting oral health and immune health. Streptococcus salivarius reduced inflammation and colitis in an animal model of gut health. Strep mitis, Strep vestibularis, and Strep sanguinis have also shown anti-inflammatory action in the mouth.4

As long as dietary carbohydrates are kept in check, these healthy streptococci mouth bacteria are plentiful on teeth. We will discuss carbohydrates later when we talk about how to build a healthy Streptococcus oral microbiome. Scientists suggest that our commensal Streptococcus species might even be our best weapon to fight cavities!3


Image by Sabrina B. from Pixabay

“Bad” Streptococcus Can Cause Strep Throat, Pneumonia, Cavities, and Worse

Most Streptococcus bacteria are harmless or beneficial. But the bad guys get the lion’s share of our attention. You probably learned about Streptococcus bacteria before you turned five years old. Why? Because of strep throat, which is believed to be caused by the pathogen Streptococcus pyogenes, also known as Streptococcus Group A.  Scarlet fever or rheumatic fever is credited to this “bad” Group A Strep, as well as Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections (PANDAS). Streptococcus pneumoniae can cause- you guessed it- pneumonia. It can also cause ear infections and even blood infections in children. Streptococcus mutans and Streptococcus sobrinus have earned the reputation of promoting cavities. If you’ve had a baby, you’ve surely heard about Streptococcus agalactiae (or Group B Streptococcus). Group B Strep is common in the gut and reproductive tracts of men and women, but it can harm some babies if they come into contact with it during vaginal birth. In general, when the microbiome gets out of balance or the immune system gets weak, these bad Streptococcus species (or pathogens) can rise to power and cause real trouble for certain people.


Your Oral Microbiome Hero: Streptococcus salivarius

Streptococcus salivarius is a normal human mouth bacteria that is generally associated with good oral health.4 It was originally isolated from a healthy adult. It is found in human breast milk and is naturally transferred to nursing babies.5

Streptococcus salivarius is well known to suppress oral pathogens. One way it does this is by making bacteriocins, which are natural antimicrobial compounds that suppress the growth of other microbes. It can stop the growth of Streptococcus pneumoniae (a pathogen that lives in the nose and throat that can cause pneumonia) and the oral pathogen Streptococcus pyogenes (which causes strep throat). It can make it difficult for Streptococcus pneumoniae bacteria to bind to throat cells.4

Strep salivarius tunes the immune system and squashes inflammation. It inhibited the release of inflammatory cytokines (IL-6 and IL-8) by three pathogens that can cause gum disease: Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Fusobacterium nucleatum.

Streptococcus salivarius M18 and K12

I call Strep salivarius my favorite oral probiotic, but in truth it’s not just one. There are two different probiotic strains of Strep salivarius– M18 and K12. Think “M” for mouth. Strep salivarius M18 works in the mouth. It can reduce dental plaque and the cavity-promoting bacterium, Streptococcus mutans.4

Streptococcus salivarius M18 can reduce a type of plaque that produces black stains (which is high in insoluble iron, creating a dark color) on teeth. In a study of 54 children who had a dental cleaning to remove black stains, children were given 1 billion cells of BLIS M18 (as a slowly dissolving tablet) daily for three months. Only 21.2% of the children who took Strep salivarius developed black stains compared to 50% of those who did not receive the probiotic.

The improvements seemed to stick. Three months after supplementation ended, 32.1% of the kids who took the dental probiotic developed black stains, whereas 53.8% of the non-supplementing group had black stains.

Streptococcus salivarius K12 works in the ear and throat. Streptococcus salivarius K12 can prevent strep throat (or streptococcal induced pharyngitis) in adults and kids. K12 can reduce bad breath by suppressing the bacteria that make bad-smelling sulfur compounds.4 It reduces ear infections, pathogens that cause ear infections, and the antibiotics needed to treat them. K12 doesn’t stop there. When kids take Strep salivarius K12, it prevents tonsil infections, reduces the need for antibiotics, school absences, and surgery.6 Seriously, this is a parent’s dream come true!

Photo by Jose Ibarra on Unsplash

Streptococcus salivarius M18

  • Reduces plaque
  • Reduces cavity-promoting bacterium, S. mutans
  • Reduces black stains on children’s teeth7
  • Prevents gum disease

Streptococcus salivarius K12

  • Lowers plaque8
  • Reduces strep throat in adults and kids
  • Decreases bad breath
  • Reduces recurrent respiratory tract infections9
  • Reduces pathogens that cause ear infections10
  • Decreases tonsil infections6
  • Crowds out Candida albicans (yeast) cells11
  • Prevents gum disease


What’s not to love? However, Streptococcus salivarius is not always an angel.12,13 Just like any microbe, it can overgrow and cause disease in someone who is immune suppressed or chronically ill. Even good, healthy microbes can grow out of control under unfavorable circumstances.


Conditions that may benefit from Streptococcus salivarius oral probiotic:

  • Bad breath
  • Cavities
  • Ear infections
  • Group B Strep imbalance (Streptococcus agalactiae)
  • Gum disease
  • Oral thrush or Candida overgrowth in the mouth
  • Recurrent strep throat
  • Recurrent antibiotics for any of these reasons
  • Throat infections
  • Tonsil infections

Oral Microbiome Expert

Oral Probiotics

Probiotic supplements for oral health often contain Lactobacillus or Bifidobacteria species. They can crowd out cavity-promoting bacteria like Streptococcus mutans and the bacteria that cause gum disease. They can improve gum health and prevent cavities. I discuss how oral probiotics affect cavities and gum disease in my book, Heal Your Oral Microbiome.

Streptococcus salivarius has some advantages. Strep salivarius is a normal, natural colonizer of the human mouth. Not so much with Lactobacillus and Bifidobacteria species. Unlike Lactobacillus species, Streptococcus doesn’t produce acid, which can be better for the teeth and for the oral microbiome.

As a probiotic supplement, Strep salivarius has been proven to be safe. Even better, after taking Strep salivarius, it actually sticks. It can persist on the tongue and mouth lining even when you aren’t taking this probiotic anymore.4 As a probiotic, Strep salivarius seems to promote a healthy immune response in the mouth and suppress inflammatory pathogens, without disrupting the natural microbiome.4 However, other Streptococcus species for oral health may emerge on the market eventually, such as Streptococcus dentisani and Streptococcus A12.3

Benefits of Streptococcus salivarius (both K12 and M18)

  • Healthy human oral bacteria
  • Safe track record14
  • Naturally colonizes the mouth
  • As a probiotic supplement, persists after discontinuing
  • Prevents gum disease
  • Fights off oral pathogens
  • Promotes a healthy immune response (anti-inflammatory)
  • Suppresses inflammatory response to pathogens4
  • Can reduce ear infections in children and the need for antibiotics15


Promote a Healthy Balance of Streptococcus Bacteria for Oral Health

Here are some steps you can take, in addition to brushing and flossing, to foster a healthy Streptococcus community in your body and ward off the “bad” Streptococcus.

A whole foods diet with fiber, colorful vegetables and fruits, and complex carbohydrates. A more primitive, unprocessed diet, like the one of our ancestors, supports a healthy oral microbiome.3

Avoid sugar and refined carbohydrates as much as possible. Streptococcus bacteria thrive on a wide selection of carbohydrates, so choose carbs wisely. The Standard American Diet of highly processed foods encourages Streptococcus mutans to overgrow and cause cavities. It probably harms the balance of other healthy Strep species in the body as well. It also increases the rates of obesity, diabetes, heart disease, and cancers.

Prebiotics. Eating a diet of fiber and colorful vegetables and fruits provides wonderful prebiotics for your healthy oral bacteria. However, you can also supplement with oral prebiotics. Hyperbiotics sells a prebiotic product that Dr. Burhenne endorses.

Probiotics for the mouth. SUPER TEETH has a dental probiotic containing Strep salivarius M18 as well as prebiotics. They are a US family company and do third-party testing on their product. BLIS sells M18 and K12 dental probiotics. They discovered the Strep salivarius probiotic line and you will often see BLIS M18 or BLIS K12 on the ingredient labels for oral health formulas. Doses of Streptococcus salivarius range from one to two billion colony forming units/gram (CFU/g) per day. Lozenges or tablets are taken after brushing teeth or away from food and water. Treatment may last four to six weeks or longer. The higher end of this dosing range is ideal if treating disease or oral dysbiosis. For health maintenance, the lower end of this dose range is appropriate.

Saliva flow. Healthy flowing saliva is critical for your oral microbiome. Stay hydrated, eat chewy things such as xylitol gum, try salty things that might make you thirstier, and avoid medications that dry the mouth. If you have unexplained dry mouth, see a functional medicine clinician to determine the root cause.

Nose breathing is the best way to breathe. If you are a mouth breather, look into ways to shift toward mouth breathing, such as mouth taping at night. See a sleep dentist who can assess your breathing.

Test for Streptococcus salivarius and other Streptococcus bacteria. Bristle offers a simple oral microbiome saliva test that analyzes a host of oral bacteria including the commensal Streptococcus species mentioned in this blog. Use the code “CASS15” to get 15% off your test.

Boost the immune system. The microbiome and immune system work hand in hand. Getting rid of allergenic foods such as dairy (mentioned earlier) can help the immune system heal and focus on what it needs to be doing. Supplements such as immunoglobulins can promote immune health, larch arabinogalactan (a prebiotic), and probiotics for gut health can all help.

Look for other root causes for imbalanced Streptococcus bacteria. Eating dairy can predispose people to recurrent strep throat infections and ear infections. Recurrent infections are a sign that there is a root cause that hasn’t been addressed. Try eliminating dairy and the top allergens for a month to see if recurrent infections stop or slow down. If there are signs of gut dysbiosis, such as constipation, diarrhea, bloating, heartburn, loose stools, abdominal pain, then the gut might be involved in oral infections. Work with an integrative and functional medicine provider to guide you.

Harness the Power of Friendly Streptococcus Bacteria for Better Health

Streptococcus bacteria are ancient and vital players in the human microbiome. They are found all over and in the human body. When Streptococcus bacteria turn “bad” and harm us, it is usually due to an imbalance in the microbiome or a weakened immune system. Promote a healthy oral microbiome and healthy Streptococcus bacteria with a whole foods primitive diet, Streptococcus salivarius M18 and K12, colorful veggies and fruits, prebiotics, and avoiding allergenic foods. Strep salivarius M18 and K12 are natural inhabitants of the healthy mouth. They ward off pathogens and fight disease. By fostering a healthy community of Streptococcus, we can prevent recurrent ear infections, strep throat infections, cavities, and lung infections such as pneumonia. We can harness the power of our commensal Streptococcus species to improve mouth, throat, and ear health.



  1. Abranches J, Zeng L, Kajfasz JK, et al. Biology of Oral Streptococci. Microbiology spectrum. 2018;6(5).
  2. Sedghi L, DiMassa V, Harrington A, Lynch SV, Kapila YL. The oral microbiome: Role of key organisms and complex networks in oral health and disease. Periodontology 2000. 2021;87(1):107-131.
  3. Baker JL, Edlund A. Exploiting the Oral Microbiome to Prevent Tooth Decay: Has Evolution Already Provided the Best Tools? Front Microbiol. 2018;9:3323.
  4. MacDonald KW, Chanyi RM, Macklaim JM, Cadieux PA, Reid G, Burton JP. Streptococcus salivarius inhibits immune activation by periodontal disease pathogens. BMC Oral Health. 2021;21(1):245.
  5. Li S, Li N, Wang C, et al. Gut Microbiota and Immune Modulatory Properties of Human Breast Milk Streptococcus salivarius and S. parasanguinis Strains. Front Nutr. 2022;9:798403.
  6. Marini G, Sitzia E, Panatta ML, De Vincentiis GC. Pilot study to explore the prophylactic efficacy of oral probiotic Streptococcus salivarius K12 in preventing recurrent pharyngo-tonsillar episodes in pediatric patients. Int J Gen Med. 2019;12:213-217.
  7. Bardellini E, Amadori F, Gobbi E, Ferri A, Conti G, Majorana A. Does Streptococcus Salivarius Strain M18 Assumption Make Black Stains Disappear in Children? Oral health & preventive dentistry. 2020;18(1):161-164.
  8. Babina K, Salikhova D, Polyakova M, et al. The Effect of Oral Probiotics (Streptococcus Salivarius k12) on the Salivary Level of Secretory Immunoglobulin A, Salivation Rate, and Oral Biofilm: A Pilot Randomized Clinical Trial. Nutrients. 2022;14(5).
  9. Cernioglo K, Kalanetra KM, Meier A, et al. Multi-Strain Probiotic Supplementation with a Product Containing Human-Native S. salivarius K12 in Healthy Adults Increases Oral S. salivarius. Nutrients. 2021;13(12).
  10. Chen TY, Hale JDF, Tagg JR, et al. In vitro Inhibition of Clinical Isolates of Otitis Media Pathogens by the Probiotic Streptococcus salivarius BLIS K12. Probiotics and antimicrobial proteins. 2021;13(3):734-738.
  11. Mokhtar M, Rismayuddin NAR, Mat Yassim AS, et al. Streptococcus salivarius K12 inhibits Candida albicans aggregation, biofilm formation and dimorphism. Biofouling. 2021;37(7):767-776.
  12. Ahmad S, Song D, Reyes JVM, Whiting A, Almas T, Lieber JJ. Hakuna mycotic aneurysm, Streptococcus salivarius does not always mean “no worries”. Ann Med Surg (Lond). 2021;69:102798.
  13. Chaker H, Brahim RB, Toumi S, et al. Unusual Cause of Peritonitis in Peritoneal Dialysis Patient Related to Streptococcus salivarius. Saudi journal of kidney diseases and transplantation : an official publication of the Saudi Center for Organ Transplantation, Saudi Arabia. 2021;32(3):838-840.
  14. Hale JDF, Jain R, Wescombe PA, Burton JP, Simon RR, Tagg JR. Safety assessment of Streptococcus salivarius M18 a probiotic for oral health. Benef Microbes. 2022;13(1):47-60.
  15. Cantarutti A, Rea F, Dona D, et al. Preventing recurrent acute otitis media with Streptococcus salivarius 24SMB and Streptococcus oralis 89a five months intermittent treatment: An observational prospective cohort study. International journal of pediatric otorhinolaryngology. 2020;132:109921.


Cass Nelson-Dooley, M.S.

Cass Nelson-Dooley, M.S.

Cass Nelson-Dooley, MS, is a researcher, author, educator, and laboratory consultant. She studied medicinal plants in the rain forests of Panama as a Fulbright Scholar and then launched a career in science and natural medicine. Early on, she studied ethnobotany, ethnopharmacology, and drug discovery at the University of Georgia and AptoTec, Inc. She joined innovators at Metametrix Clinical Laboratory as a medical education consultant helping clinicians use integrative and functional laboratory results in clinical practice. She owns Health First Consulting, LLC, a medical communications company with the mission to improve human health using the written word. Ms. Nelson-Dooley is an oral microbiome expert and author of Heal Your Oral Microbiome. She was a contributing author in Laboratory Evaluations for Integrative and Functional Medicine and Case Studies in Integrative and Functional Medicine. She has published case studies, book chapters, and journal articles about the oral microbiome, natural medicine, nutrition, laboratory testing, obesity, and osteoporosis.