- Oral Microbiome Library
- Gums
- P. intermedia
Prevotella intermedia
Also called the bleeding-gum bacterium
- Evidence
- Moderate evidenceModerate for gum inflammation · Rises with pregnancy hormones
- Class
- Bacterium · Gum pocket · panel code Pi
- Sources
- 4 peer-reviewed sources
Key takeaway
P. intermedia is an “orange complex” bacterium that climbs in inflamed, bleeding gums and famously surges during pregnancy, when it can use the hormones estrogen and progesterone as growth factors [1][2].
| What it is | A black-pigmented, anaerobic, Gram-negative rod. |
|---|---|
| Where it lives | Inflamed gum pockets; also in some tonsil and sinus infections. |
| Role in the mouth | Part of the orange complex that paves the way for red-complex species [1]. |
| Beyond the mouth | Associated with pregnancy gingivitis and studied in respiratory and other infections [3]. |
| Evidence strength | Moderate evidence. Consistent human associations, with mechanism supported mainly by lab work. |
| 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. |
What is Prevotella intermedia?
P. intermedia belongs to the orange complex, the cluster of species that increases as gingivitis sets in and that tends to precede and accompany the red complex in deeper pockets [1].
It is one of the species most responsive to the body’s hormones. In a 1980 study of pregnant women, its proportion in plaque rose sharply in the second trimester alongside gum inflammation, and lab work showed it could substitute estradiol and progesterone for the vitamin K it normally needs [2].
How does P. intermedia work?
It produces proteases that break down tissue proteins and immunoglobulins, and lipopolysaccharide that drives inflammation. Its surface helps it co-aggregate with other species, so it acts as a connector within the biofilm [3].
Inflammation feeds it. Bleeding gums release iron-rich compounds and proteins that black-pigmented species like P. intermedia thrive on, a loop that helps explain why gingivitis can accelerate once started [3].
What does the research show?
Human studies consistently find P. intermedia more abundant in gingivitis and periodontitis than in health and track it with bleeding on probing [1]. An experimental gingivitis study in pregnant women confirmed the clinical, hormonal and microbial shift that the earlier work described [4].
Beyond the gums, a 2025 review summarised reports linking it to respiratory, abdominal and other infections, mostly from case series and small studies [3]. We grade the evidence moderate: solid for gum inflammation, thinner elsewhere.
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.
If you are pregnant, going through puberty or on hormonal medication, an elevated level is not surprising and is one reason dentists emphasise gum care during those periods [2][4].
Frequently asked questions
Why does it rise during pregnancy?
It can use estrogen and progesterone as growth factors in place of vitamin K, so it gains an advantage when those hormones rise. Pregnancy gingivitis tracks the same curve [2].
Is P. intermedia a red-complex bacterium?
No, orange complex. Orange species rise with early inflammation and set the stage for the red complex in deeper pockets [1].
Does a high level mean I have gum disease?
It means the inflammation-associated side of your plaque is active. Only an exam can tell gingivitis from periodontitis.
Sources
- 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
- Kornman KS, Loesche WJ. The subgingival microbial flora during pregnancy. J Periodontal Res 1980. DOI: 10.1111/j.1600-0765.1980.tb00265.xPMID 6103927
- Zhang S, Zhao Y, Lalsiamthara J, et al.. Current research progress on Prevotella intermedia and associated diseases. Crit Rev Microbiol 2025. DOI: 10.1080/1040841X.2024.2390594PMID 39140115
- Raber-Durlacher JE, van Steenbergen TJ, Van der Velden U, et al.. Experimental gingivitis during pregnancy and post-partum: clinical, endocrinological, and microbiological aspects. J Clin Periodontol 1994. DOI: 10.1111/j.1600-051x.1994.tb01172.xPMID 7989619
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.