How two clinically studied strains of Streptococcus salivarius support the balance of bacteria already living in your mouth.
Read time: 8 minutes
What are BLIS K12 and BLIS M18?
BLIS K12™ and BLIS M18™ are two patented strains of Streptococcus salivarius, a bacterium that naturally occupies healthy mouths. Both produce bacteriocin-like inhibitory substances, which is what the BLIS name refers to. K12 settles in the throat and upper respiratory surfaces and has been studied for throat wellness and breath.† M18 settles around the teeth and gum line and has been studied for plaque and gum health.† Both hold FDA no-objection GRAS status, K12 since 2015 and M18 since 2019.
Your Mouth Is an Ecosystem
There are hundreds of bacterial species living in your mouth and throat right now, and most of them are supposed to be there. A healthy oral environment is not a sterile one. It is a balanced one, where the resident population is established enough that there is little room left for anything else to settle.
Streptococcus salivarius is one of the most abundant residents of that environment. It is among the first species to colonize a newborn's mouth, and in most people it stays for life.
Everyday things shift that balance. Illness, dry mouth, and harsh mouth rinses all reduce the resident population along with whatever they were aimed at. Oral probiotics take the opposite approach. Rather than reducing what is there, they add back specific, well-characterized strains and let the ecosystem do the rest.†
What BLIS Actually Stands For
BLIS is short for bacteriocin-like inhibitory substances. Bacteriocins are small peptides that bacteria produce to hold their territory against competing strains. It is an ordinary part of how microbial communities regulate themselves, and it is the mechanism both of these strains were selected for.
BLIS K12 produces two of them, salivaricin A2 and salivaricin B. BLIS M18 produces salivaricin A2 and salivaricin 9, and additionally makes two enzymes, dextranase and urease, which act on the sticky matrix of dental biofilm and on the acidity of saliva respectively.
Where the strains came from: both were isolated from the mouths of healthy people by researchers at the University of Otago in New Zealand, who were studying why some individuals carry unusually strong bacteriocin-producing populations. BLIS Technologies has developed and licensed them since.
Two Strains, Two Neighborhoods
K12 and M18 are the same species, but they do not do the same job. They colonize different surfaces and have been studied against different measures.
| BLIS K12™ | BLIS M18™ | |
|---|---|---|
| Where it settles | Tongue, tonsils, throat | Tooth surfaces, gum line |
| Bacteriocins | Salivaricin A2, salivaricin B | Salivaricin A2, salivaricin 9 |
| Additional enzymes | None characterized | Dextranase, urease |
| Studied for | Throat wellness, fresh breath† | Plaque, healthy gums† |
| FDA no-objection GRAS | 2015 | 2019 |
Used together, they cover the two surfaces most people care about. Throat and breath on one side, teeth and gums on the other.†
What the Research Actually Shows
Here is where the evidence is strongest, and where it is thinner. Both are worth knowing before you buy anything.
Gum condition and plaque, the strongest evidence for M18
In a three-month double-blind, placebo-controlled trial of 62 adults, daily M18 lozenges were associated with reduced gingival bleeding from the first month onward, and reduced plaque accumulation from the second month.† A separate four-week trial in 61 younger adults found decreases in both gingival index and plaque index against placebo.
Babina et al., 2024. Dentistry Journal 12(7):222. PMID 39057009* · Babina et al., 2023. Nutrients 15(18):3882. PMID 37764667*
Breath compounds
Bad breath is largely driven by volatile sulfur compounds produced by bacteria on the tongue. In an early study of 23 people, 85% of those given K12 showed substantial reductions in these compounds one week later, against 30% on placebo.† Two things to note honestly: that is the proportion of people who responded, not the size of the reduction, and every participant used a chlorhexidine rinse first. It was a preliminary study, and a small one.
Burton et al., 2006. Journal of Applied Microbiology 100(4):754–64. PMID 16553730*
Laboratory work on the mechanism
In laboratory culture, not in people, K12 and M18 both reduced the release of the sulfur compounds behind oral malodor across six species, and lowered expression of a protease made by Porphyromonas gingivalis. Notably, the strains' culture supernatant alone reproduced the effect, which points to secreted compounds rather than competition for space. This is mechanistic evidence. It explains how the strains might work, and it is not a clinical outcome.
Park et al., 2023. Oral Health & Preventive Dentistry 21:259–270. PMID 37724895* · In-vitro study
Where the evidence is thin
A 2023 trial found that K12 raised salivary immunoglobulin A in young adults during a demanding training block. It is a real finding, but it came from 20 participants, and the number of illness episodes did not differ between the groups. Salivary IgA is a marker, not an outcome. Anyone presenting that study as proof of a benefit is reading more into it than it says.
Bertuccioli et al., 2023. Frontiers in Immunology 14:1129060. PMID 36936914*
Adding, Not Replacing
One question worth asking about any oral probiotic is whether introducing a large dose of one organism disturbs everything else.
A 2021 double-blind trial looked at exactly that. Two weeks of supplementation raised salivary K12 levels by roughly five orders of magnitude, and the overall composition of the oral microbiome was unchanged. Levels returned to baseline about two weeks after people stopped.†
That second detail matters as much as the first. Colonization is real while you are taking it, and it fades when you stop.
The short version: an oral probiotic adds to the resident population rather than reshaping it, and the addition is temporary.† Cernioglo et al., 2021. Nutrients 13(12):4392. PMID 34959944*
Why the Strain Code Matters
K12 and M18 are not marketing names. They are strain designations, and within a single bacterial species different strains can behave very differently. Streptococcus salivarius is a common species, but the specific bacteriocin and enzyme profile that these two strains were selected for is not something every member of the species carries.
All of the research on this page was conducted on these exact strains. A label that says only Streptococcus salivarius, with no strain code after it, is not describing the same organism, and none of these findings transfer to it.
So when you read a supplement label, look past the species name to the code that follows it. That code is the thing the studies were run on.
How to Take an Oral Probiotic
Oral probiotics work differently from the gut kind. Gut probiotics have to survive stomach acid to reach where they are going. These do not travel. They act at the surfaces in your mouth and throat, which changes how you should take them.
Take it after brushing, at night
Brushing clears the surfaces the strains need to settle on, and overnight there is less swallowing and less saliva flow to wash them away. It is the longest undisturbed contact window of the day.
Chew it slowly and let it dissolve
Do not swallow it whole. The point is contact time with the tissues of the mouth and throat, so let a chewable tablet break down and spread rather than sending it straight down.
Wait 30 minutes before eating or drinking
Anything you eat or drink rinses the surfaces you just seeded. Thirty minutes is a reasonable window to let the strains settle.
Take it every day
This is the one people get wrong. In the three-month M18 trial, benefits built month over month, and the authors noted that a lasting effect after stopping should not be expected, concluding that intake needs to be ongoing. The colonization study found the same thing from the other direction, with levels returning to baseline about two weeks after supplementation ended. Sporadic use does not produce a sustained population.
Who It Suits
Oral probiotics are for adults who want to support the oral environment alongside normal dental care rather than instead of it. That tends to mean:
- People who are conscious of breath freshness through the day†
- People who want to support healthy gums and manage plaque between cleanings†
- People who train hard, travel often, or otherwise spend time in dry, dehydrating environments
- Anyone who brushes and flosses well and wants to add one more step that is easy to keep up
None of this replaces brushing, flossing, or seeing a dentist. It sits alongside them.
Common Questions
How long before I notice anything?
In the published trials, measurable changes in gum condition appeared from about one month, with plaque measures following in the second and third months. Breath compounds shifted faster in the early study, within a week. Individual results vary.
Can I take it with a mouthwash?
Strong mouth rinses reduce the population you are trying to establish, so keep them apart in time. If you use one, use it well before the tablet rather than after.
Is this the same as a gut probiotic?
No. Gut probiotics are formulated to survive stomach acid and act in the intestine. Oral probiotics act on the surfaces of the mouth and throat, which is why the format is a chewable rather than a capsule.
Does it need refrigeration?
No. Store it at room temperature, away from heat and direct light.
What does 4 billion CFU mean?
CFU stands for colony forming units, the count of viable bacterial cells in a dose. Published trials on these strains have used doses ranging from roughly half a billion to ten billion CFU per day, so a higher number on a label does not automatically mean a better formula. What matters is that the strains are the ones that were studied and that they are alive when you take them.
Consult a healthcare provider before starting any new supplement.
NUTRAFORM Advanced Oral Probiotics
BLIS K12™ and BLIS M18™ alongside five further strains selected for the oral environment. 4 billion CFU in one chewable tablet, natural spearmint, 30-day supply. Third party lab tested, manufactured in a cGMP-certified US facility. Dentist formulated.
Shop Advanced Oral Probiotics†These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.
References
- Babina, K., et al. (2024). A three-month probiotic (the S. salivarius M18 strain) supplementation decreases gingival bleeding and plaque accumulation: a randomized clinical trial. Dentistry Journal, 12(7), 222. PMID 39057009
- Babina, K., et al. (2023). Antigingivitis and antiplaque effects of oral probiotic containing the S. salivarius M18 strain: a randomized clinical trial. Nutrients, 15(18), 3882. PMID 37764667
- Park, J.-A., et al. (2023). Oral probiotics, Streptococcus salivarius K12 and M18, suppress the release of volatile sulfur compounds and a virulent protease from oral bacteria: an in-vitro study. Oral Health & Preventive Dentistry, 21, 259–270. PMID 37724895
- Burton, J. P., et al. (2006). A preliminary study of the effect of probiotic Streptococcus salivarius K12 on oral malodour parameters. Journal of Applied Microbiology, 100(4), 754–64. PMID 16553730
- Bertuccioli, A., et al. (2023). Use of Streptococcus salivarius K12 in supporting the mucosal immune function of active young subjects: a randomised double-blind study. Frontiers in Immunology, 14, 1129060. PMID 36936914
- Cernioglo, K., et al. (2021). Multi-strain probiotic supplementation with a product containing human-native S. salivarius K12 in healthy adults increases oral S. salivarius. Nutrients, 13(12), 4392. PMID 34959944
