Oral vs. gut microbiome
You've heard about your gut microbiome. Your mouth has one of its own.
Two connected ecosystems with different residents, different chemistry, and different jobs.
The mouth and the gut are both microbial ecosystems, and they are connected — you swallow saliva all day. But they are not versions of the same thing. The mouth is aerobic at the surface and low in oxygen below the gumline, washed constantly by saliva, and it is the only place in the body with hard, non-shedding surfaces for bacteria to build on. The gut is anaerobic, far longer in transit, and lined with mucus over cells that renew continuously. Different environments select different residents, so the organisms that thrive in one are largely not the ones that thrive in the other. A stool sample describes the gut. A saliva sample describes the mouth.
Two connected ecosystems
They are continuous — the mouth opens onto the digestive tract, and roughly a litre of saliva carrying oral organisms is swallowed every day. Connection is not the same as similarity, though, and most oral organisms do not establish themselves downstream.
Different environments
The differences are structural, not incidental.
Different conditions select different residents.
| The mouth | The gut | |
|---|---|---|
| Oxygen | Aerobic at the surface, low-oxygen in pockets and coating | Largely anaerobic |
| Surfaces | Teeth — hard and non-shedding | Mucus over continuously renewing cells |
| Flow | Constant saliva, frequent disturbance | Slower transit |
| Structure | Layered biofilms on fixed surfaces | Communities in lumen and mucus |
| Chemistry | Shifts with every meal, buffered by saliva | More stable, further from the mouth |
Different dominant residents
Streptococci dominate early oral colonisation, alongside Actinomyces, Veillonella, Rothia, Neisseria and — in the low-oxygen spaces — the organisms associated with periodontal disease.
Gut communities are dominated by very different groups. Where a genus appears in both, the species and strains usually differ, which is why a finding in one site does not transfer to the other.
How organisms travel from mouth to gut
Swallowed saliva carries oral organisms downstream continuously. Most do not establish there — stomach acid and a very different environment see to that — but the traffic is constant and measurable.
Why oral organisms draw research attention
Some organisms associated with periodontal disease have been reported in tissues elsewhere in the body, and oral health has been associated in research with several systemic conditions.
These are associations reported in study populations. They are an active area of research rather than a settled mechanism, and the evidence labels below reflect that.
Each test samples its own ecosystem
A stool sample reflects the gut community. A saliva sample reflects the mouth. Each describes the environment it came from, and neither substitutes for the other.
If you have had a gut microbiome test, it told you about your gut. It did not describe your mouth, because it never sampled it.
Where the research is
Where the relevant findings sit.
The mouth and gut host distinct microbial communities shaped by different physical and chemical conditions.
Swallowed saliva transports oral organisms to the digestive tract continuously.
The mouth is the only site in the body with hard, non-shedding surfaces for biofilm formation.
Oral organisms have been reported in tissues elsewhere in the body.
Oral health has been associated with several systemic conditions in study populations.
Which oral organisms establish downstream, in whom, and under what conditions.
In context
Sampling site
A measurement describes the site it sampled. That is a property of sampling, not a limitation of either method.
Diet
Diet moves both communities, through different mechanisms — sugar frequency and dietary nitrate matter in the mouth for reasons specific to it.
Medication
Antibiotics act on both. Several common medications reduce saliva flow, which changes the oral environment specifically.
The clinical exam
Neither microbiome measurement replaces an examination of the tissue it describes.
How OraPath measures this
The Oral Balance Test samples saliva, which carries organisms shed from across the whole mouth — tongue, cheeks, gumline — and reports sixteen targeted organisms and functions, each at its own Detection Level.
It describes the oral ecosystem. Nothing in it is a measurement of the gut.
You know your gut. Now meet your mouth.
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
Is the oral microbiome part of the gut microbiome?
They are connected but distinct. The mouth is the start of the digestive tract, and swallowed saliva carries organisms downstream, but the resident communities differ because the environments differ.
Can a gut microbiome test tell me about my mouth?
It describes the sample it was given. A stool sample reflects the gut community; it does not sample the mouth.
Do oral bacteria reach the gut?
Continuously, in swallowed saliva. Most do not establish there. Which ones do, and in whom, is an active area of study.
Why is the mouth a different environment?
Oxygen gradients, constant saliva flow, chemistry that shifts with every meal, and hard non-shedding surfaces — teeth — that exist nowhere else in the body.
Should I test both?
They answer different questions about different parts of you. Which is useful depends on what you want to know.
References
- Kilian M, Chapple ILC, Hannig M, et al. The oral microbiome — an update for oral healthcare professionals. Clin Microbiol Infect. 2016;22:657–666.
- Lamont RJ, Koo H, Hajishengallis G. The oral microbiota: dynamic communities and host interactions. Nat Rev Microbiol. 2018;16:745–759.
- Marsh PD. Are dental diseases examples of ecological catastrophes? Microbiology. 2003;149:279–294.
Laboratory developed test · for adjunctive clinical use · not FDA cleared.