Good oral bacteria
Some of the bacteria in your mouth are on your side.
Protective species hold territory, crowd out disruptive ones, and carry out functions your body relies on.
Most bacteria in your mouth are not a problem, and some are actively useful. Commensal organisms occupy surfaces and consume nutrients that disruptive species would otherwise use — a phenomenon called colonisation resistance. A well-established community is simply harder to move into. Some oral bacteria also perform a job the body uses: converting dietary nitrate to nitrite, the first step of a pathway human cells do not efficiently carry out themselves. That is why “kill the bacteria” misreads the mouth. Broad antimicrobial approaches act on the whole community, including the part holding territory on your behalf. A routine that helps is one that works with that side rather than trying to clear the field.
Why “kill the bacteria” misreads the mouth
The mouth is not meant to be sterile and cannot be made so. It is a colonised surface, and the question is which community occupies it.
Broad antimicrobial approaches act on everything present, including the organisms whose occupancy is the reason disruptive species have nowhere to settle.
Colonisation resistance
An established community resists newcomers. The surfaces are taken, the nutrients are being consumed, and the local chemistry is already set by whoever is there.
This is the main protective mechanism in the mouth, and it is structural rather than active — it works by occupancy.
Competition for niches
Organisms compete for attachment sites and for nutrients, and some produce compounds that inhibit their neighbours directly. Others simply grow faster on what is available.
The result is an equilibrium that holds until something shifts it — diet, saliva flow, antimicrobials, or inflammation changing the habitat.
The commensal streptococci
Three appear on the Balance Test's protective side.
Streptococcus sanguinis is an early coloniser of tooth surfaces and is associated with periodontal health. Streptococcus mitis is among the most common organisms in a balanced mouth. Streptococcus salivarius is one of the most abundant residents of the tongue, and is found more often in mouths without persistent odour.
These are ordinary residents. Their value is in being present and established.
Nitrate reducers as a functional community
This group is defined by what it does rather than by taxonomy. Certain oral bacteria reduce dietary nitrate to nitrite — a conversion human cells do not perform efficiently — and the body uses the product downstream.
It is the clearest example of the oral community doing something for the rest of the body rather than merely occupying space in it.
What disrupts the protective side
Antimicrobial rinses act broadly rather than selectively, and chlorhexidine in particular has been shown to substantially reduce nitrate-reducing organisms. Antibiotics act on the oral community as well as the target. Smoking changes composition. Dry mouth removes the flow that the surface depends on. And inflammation changes the habitat in ways that favour the other side.
Supporting a resilient community
Mechanical plaque control removes accumulation without sterilising. Dietary nitrate from leafy greens and beets feeds the nitrate-reducing side. Limiting how often fermentable carbohydrate arrives limits acid episodes. Managing dry mouth preserves flow.
The framing that helps is tending a community rather than clearing one.
Where the research is
Where the relevant findings sit.
Commensal organisms resist colonisation by competing for surfaces and nutrients.
Oral bacteria reduce dietary nitrate to nitrite; human cells do not perform this step efficiently.
Chlorhexidine substantially reduces oral nitrate-reducing bacteria.
Commensal streptococci are associated with periodontal health in comparative studies.
The balance between commensal and disease-associated organisms appears to matter more than the presence of any single species.
How durably a protective community can be re-established once it has been depleted.
In context
Diet
Dietary nitrate feeds the nitrate-reducing side; carbohydrate frequency feeds the acid-producing side. Both move the balance.
Antimicrobials
Rinses and antibiotics act on the whole community. What is used, and how often, changes the protective side too.
Saliva
Flow supplies minerals, buffers acid and clears surfaces. Reduced flow changes conditions for everything living there.
The clinical exam
The protective side is a description of the community. What is happening in the tissue is a separate measurement.
How OraPath measures this
The Oral Balance Test reports the protective side separately rather than netting it against the disruptive side. Three commensal streptococci and the nitrate-reducing capacity feed a protective capacity reading.
Keeping it separate is deliberate: a mouth with a strong protective side and high disruptive pressure is in a different position from one where both are low, and a single combined number would hide that.
See which side is holding territory.
Curious what your oral microbiome looks like? The Oral Balance Test measures targeted organisms and microbial functions from a saliva sample processed in our Norman, Oklahoma laboratory.
Common questions
Are there good bacteria in the mouth?
Most oral bacteria are ordinary residents, and some are useful — they occupy surfaces disruptive species would otherwise take, and some carry out nitrate reduction the body uses downstream.
Does mouthwash kill good bacteria too?
Antimicrobial rinses act broadly rather than selectively. Chlorhexidine in particular has been shown to substantially reduce nitrate-reducing organisms.
What is colonisation resistance?
An established community is harder to move into, because the surfaces are occupied and the nutrients are being used. It is protection by occupancy.
Which bacteria are the protective ones?
On the Balance Test: S. salivarius, S. sanguinis and S. mitis, plus the nitrate-reducing capacity, which is measured as a function rather than a species list.
Can the protective side be rebuilt?
Communities respond to what changes around them. How durably a depleted protective community re-establishes is an active area of study.
References
- Rosier BT, Marsh PD, Mira A. Resilience of the oral microbiota in health. J Dent Res. 2018;97:371–380.
- Rosier BT, Takahashi N, Zaura E, Krom BP, Marsh PD. The importance of nitrate reduction for oral health. J Dent Res. 2022;101(8):887–897.
- Kilian M, Chapple ILC, Hannig M, et al. The oral microbiome — an update for oral healthcare professionals. Clin Microbiol Infect. 2016;22:657–666.
- Marsh PD. Are dental diseases examples of ecological catastrophes? Microbiology. 2003;149:279–294.
Laboratory developed test · for adjunctive clinical use · not FDA cleared.