Streptococcus salivarius
EVIDENCE: MODERATEAlso sold as: S. salivarius, BLIS K12, BLIS M18, oral streptococcus probiotic
S. salivarius occurs naturally in the mouth. Specific K12 and M18 strains have trials concerning breath, throat, and oral health. A species name and a weight such as 20 mg do not establish the strain or live-bacteria count used in those studies.
Compiled by iSupplementReviews editorial team ·Updated 2026-10-06 · 4 sources
- Type
- Probiotic — oral/ENT species
- Studied dose
- ≥1×10⁹ CFU/day (K12 lozenges; school trial used 2.5×10⁹ CFU/lozenge)
- Best form
- Named BLIS strain (K12 for breath/throat, M18 for plaque/cavities) in a slow-dissolve lozenge with a stated CFU count
- Our rating
- MODERATE — Several human trials — limits in size, duration, or independence
What is Streptococcus salivarius?
S. salivarius commonly lives on the tongue and in the throat. It differs from S. pyogenes, the species associated with strep throat. Specific strains, mainly BLIS K12 and M18 developed in New Zealand, have oral and throat research.
Other names and forms it’s sold as
- BLIS K12: the main ingredient strain; produces salivaricin antimicrobial peptides that suppress S. pyogenes and breath-odor bacteria
- BLIS M18: the dental-plaque strain, studied for cavity-related outcomes
- Generic “S. salivarius”: species-only labeling; unverifiable against the strain-specific evidence
- Slow-dissolve lozenges: the studied delivery form (oral contact time is the mechanism)
Where does it come from?
The human mouth itself: K12 was isolated from a healthy New Zealand schoolchild’s throat. Commercial material is a cultured isolate of that exact strain.
How does it work in the body?
K12 produces two antimicrobial peptides, salivaricin A2 and salivaricin B, that directly inhibit S. pyogenes, H. influenzae, and other oral/ENT pathogens. Colonization studies show the strain can persist in the nasopharynx for ~32 days after dosing stops. It also shifts the measurable saliva and nasopharyngeal microbiome in trial sampling.
What is it claimed to do?
Fresher breath, throat and tonsil protection, sinus/ear support, “balanced mouth bacteria.” The breath and throat claims have real trials behind them (for K12 specifically); sinus and ear outcomes are thinner.
What does the research show?
| Claim | Evidence | Dose studied | Verdict |
|---|---|---|---|
| Reduced strep throat recurrence (children) | Positive Italian studies + one large null NZ school trial | ≥1×10⁹–2.5×10⁹ CFU/lozenge | Mixed — promising, not settled |
| Bad breath / volatile sulfur compounds | Small human trials (K12) | ~1×10⁹ CFU/day | Plausible — best-studied claim |
| Nasopharyngeal colonization | Trial-documented | ~1×10⁹ CFU/day | Supported — the mechanism works |
| Gum/cavity outcomes | M18-specific, thinner data | ~1×10⁹ CFU/day | Plausible, M18 only |
The evidence, both directions
The positive line: in recurrent-strep children, K12 lozenges (≥1B CFU/tablet, 90 days) were associated with ~90% fewer streptococcal episodes in Italian pilot work, and microbiome trials confirm K12 colonizes the nasopharynx and shifts salivary flora. The counterweight: the largest test, a 2017 New Zealand school trial (N=1,314 children, 2.5×10⁹ CFU/lozenge daily for a school year), found only an 11.2% relative reduction in culture-positive sore throats, nonsignificant. The strongest study produced the weakest result.
What dose was studied?
| Goal | Dose | Form/route | Duration |
|---|---|---|---|
| Strep throat prevention | 1–2.5×10⁹ CFU/day | slow-dissolve lozenge | 90 days–school year |
| Breath/microbiome | ~1×10⁹ CFU/day | lozenge | 2–4 weeks |
Side effects
Excellent safety record: K12 carries an unusually clean profile even among probiotics (documented antibiotic-sensitivity, no disease-causing markers). The class-level immunocompromised caution applies.
Drug interactions
- Antibiotics: space doses or take after the course; the bacteria can be killed by the drug
- Immunosuppressants: standard class caution for the severely immunocompromised
Who should not take it?
Severely immunocompromised or critically ill patients. Otherwise among the safest probiotic organisms sold; it is, after all, a species most people already host.
What the authorities say
ISAPP strain-specificity applies fully: K12 and M18 are the organisms with the reviews; a label that says only “S. salivarius” (or gives milligrams instead of CFU) can’t be tied to any of it. No regulator has approved the species for disease claims; uses remain structure/function.
What to know about Streptococcus salivarius
K12 and M18 research applies to identified strains and live-bacteria counts. A label giving only S. salivarius and a weight such as 20 mg supplies neither. Species familiarity cannot establish a match to breath, throat, or dental trials.
Frequently asked questions about Streptococcus salivarius
Is Streptococcus salivarius safe — isn't streptococcus the throat-infection bacteria?
Different species. Strep throat is S. pyogenes; S. salivarius is a harmless mouth resident most people already carry, and its K12 strain suppresses S. pyogenes via antimicrobial peptides. The name similarity is misleading.
Does S. salivarius help bad breath?
The K12 strain has real human evidence for reducing volatile sulfur compounds (the breath-odor chemicals); it's the most-studied probiotic for bad breath. That evidence requires an actual K12 lozenge at ~1 billion CFU, not an unnamed species entry.
What is BLIS K12 / M18?
The two trademarked, studied S. salivarius strains from Blis Technologies: K12 targets breath and throat/ENT outcomes, M18 targets plaque and cavity-related outcomes. When a label says only 'S. salivarius,' you can't tell whether it's a BLIS strain or an unstudied one.
What dose was studied?
Around 1–2.5 billion CFU per lozenge, typically once or twice daily, dissolved slowly in the mouth. Products listing only milligrams (e.g., '20mg') haven't disclosed the unit that predicts effect: CFU.
Does it prevent strep throat?
Evidence is mixed: Italian studies in children with recurrent strep showed large reductions (~90%), but a large 2017 New Zealand school trial found only a nonsignificant ~11% reduction. Promising, not proven.
References
- [1]S. salivarius K12 vs recurrent strep pharyngotonsillitis in children — clinical report (Di Pierro et al.)
- [2]S. salivarius K12 for group A strep pharyngitis — pragmatic school trial, largely null (Pediatr Infect Dis J 2017)
- [3]S. salivarius K12 reshapes nasopharyngeal and saliva microbiome — RCT (2021)
- [4]90% strep-disease reduction with BLIS K12 in recurrent pediatric cases — pilot study
Products we reviewed containing Streptococcus salivarius
Based on recorded labels or seller-described formulas. Inclusion does not establish a match to the strains, preparations or amounts studied here; check each review's disclosure limits.