- Oral Microbiome Library
- Gums
- F. nucleatum
Fusobacterium nucleatum
Also called the bridge
- Evidence
- Strong evidenceStrong for its biofilm role · Emerging for colorectal cancer and pregnancy
- Class
- Bacterium · Gum pocket · panel code Fn
- Sources
- 9 peer-reviewed sources
Key takeaway
F. nucleatum is the plaque’s connector: a spindle-shaped bacterium that physically bridges early colonisers and late pathogens so a mature biofilm can form [1]. It is also the oral bacterium most consistently found enriched in colorectal tumours, and the subject of a 2024 Nature paper identifying the exact lineage involved [2][3].
| What it is | A long, spindle-shaped, anaerobic, Gram-negative rod. |
|---|---|
| Where it lives | Throughout plaque, above and below the gumline; abundant in gingivitis and periodontitis. |
| Role in the mouth | Co-aggregates with almost everything, linking the biofilm together and shielding anaerobes from oxygen [1]. |
| Beyond the mouth | Enriched in colorectal cancer tissue; implicated in a documented stillbirth case; studied in other cancers and pregnancy outcomes [4][5]. |
| Evidence strength | Strong evidence. Large human studies, longitudinal cohorts or consensus reports agree on its role. |
| How we measure it | Quantitative PCR (qPCR) on your saliva sample, reported as genomic copies per mL against a reference range. Ranges are for context, not diagnostic cut-offs. F. nucleatum is reported at a higher scale (×10,000/mL) because it is normally abundant. |
What is Fusobacterium nucleatum?
F. nucleatum is one of the most abundant Gram-negative species in dental plaque and belongs to the orange complex [6]. Unlike the red-complex species, it is present in most mouths; what changes in disease is how much of it there is.
A 2019 review called it “symbiont, opportunist and oncobacterium” in one breath, which captures its range: a normal resident, a periodontal partner and, outside the mouth, a suspect in colorectal cancer [4].
How does F. nucleatum work?
Its surface is covered in adhesins that let it bind both early colonisers like streptococci and late ones like P. gingivalis. Kolenbrander’s work on plaque development showed that this bridging, keeping species within reach of each other, is what lets a complex, oxygen-free biofilm build on a tooth [1].
One adhesin, FadA, binds E-cadherin on human cells. In colon cancer cell lines and in mice, FadA switched on growth signalling in tumour cells, a proposed mechanism for the cancer association [7].
What does the research show?
Two 2012 studies independently found Fusobacterium DNA enriched in colorectal tumours compared with matching normal tissue [2][8]. In 2024, researchers showed that a specific subspecies lineage, Fusobacterium nucleatum animalis clade 2, dominates the tumour niche, and that it carries traits suited to travelling from mouth to gut [3].
In pregnancy, F. nucleatum has been recovered from the placenta and amniotic fluid, and a 2010 report traced a term stillbirth to a strain matching the mother’s oral plaque [5]. Reviews of oral bacteria and cancer treat these as strong associations with a plausible mechanism, not established causation [9][4].
What does a result mean?
A detected level is information for your dentist, not a diagnosis of gum disease. Periodontitis is diagnosed by probing, bleeding and bone loss on an exam, and this result is read alongside that. Because F. nucleatum is normally present, the panel looks at how far above the reference range it sits rather than whether it is there at all.
A high level is a sign of a mature, inflamed biofilm and typically travels with the other orange and red species [6]. It is not a cancer screen, and no saliva test is.
Frequently asked questions
Does F. nucleatum cause colorectal cancer?
Not established. It is reliably enriched in tumours and has a mechanism that could promote growth, but whether it starts cancers, accelerates them or simply colonises them is still being worked out [2][4].
Is a saliva test a way to screen for cancer?
No. Oral F. nucleatum levels are a gum-health signal. Colorectal screening is done with stool tests and colonoscopy.
Why is it everywhere in plaque?
It binds to almost every other oral species and acts as a scaffold. Without bridging organisms like it, late-stage anaerobes struggle to join the biofilm [1].
Why does it have a different reporting scale?
Because it is normally abundant. The lab reports it at ×10,000 copies per mL so the number stays readable next to rarer species.
Sources
- Kolenbrander PE, Palmer RJ Jr, Periasamy S, et al.. Oral multispecies biofilm development and the key role of cell-cell distance. Nat Rev Microbiol 2010. DOI: 10.1038/nrmicro2381PMID 20514044
- Kostic AD, Gevers D, Pedamallu CS, et al.. Genomic analysis identifies association of Fusobacterium with colorectal carcinoma. Genome Res 2012. DOI: 10.1101/gr.126573.111PMID 22009990
- Zepeda-Rivera M, Minot SS, Bouzek H, et al.. A distinct Fusobacterium nucleatum clade dominates the colorectal cancer niche. Nature 2024. DOI: 10.1038/s41586-024-07182-wPMID 38509359
- Brennan CA, Garrett WS. Fusobacterium nucleatum - symbiont, opportunist and oncobacterium. Nat Rev Microbiol 2019. DOI: 10.1038/s41579-018-0129-6PMID 30546113
- Han YW, Fardini Y, Chen C, et al.. Term stillbirth caused by oral Fusobacterium nucleatum. Obstet Gynecol 2010. DOI: 10.1097/AOG.0b013e3181cb9955PMID 20093874
- Socransky SS, Haffajee AD, Cugini MA, et al.. Microbial complexes in subgingival plaque. J Clin Periodontol 1998. DOI: 10.1111/j.1600-051x.1998.tb02419.xPMID 9495612
- Rubinstein MR, Wang X, Liu W, et al.. Fusobacterium nucleatum promotes colorectal carcinogenesis by modulating E-cadherin/β-catenin signaling via its FadA adhesin. Cell Host Microbe 2013. DOI: 10.1016/j.chom.2013.07.012PMID 23954158
- Castellarin M, Warren RL, Freeman JD, et al.. Fusobacterium nucleatum infection is prevalent in human colorectal carcinoma. Genome Res 2012. DOI: 10.1101/gr.126516.111PMID 22009989
- Whitmore SE, Lamont RJ. Oral bacteria and cancer. PLoS Pathog 2014. DOI: 10.1371/journal.ppat.1003933PMID 24676390
This page is educational and does not constitute medical or dental advice, a diagnosis, or a health claim. The OneOral Bio Test reports the organisms and measurements present in a saliva sample; reference ranges are for context only and are not diagnostic thresholds. A licensed dentist reviews results in the context of your examination and history. Content reviewed by the OneOral Clinical Team; research summaries reflect the cited sources as of Oct 27, 2026.