Glossary · Dysbiosis and disease
Gardnerella vaginalis
In one sentence
Gardnerella vaginalis is a facultatively anaerobic vaginal bacterium associated with bacterial vaginosis. It is also found in women without symptoms, so its presence alone is not enough for a diagnosis.
Also known as: Gardnerella · G. vaginalis
What is Gardnerella vaginalis?
It is a small, Gram-variable, facultatively anaerobic bacterium that colonises the vagina. It is the organism most closely associated with bacterial vaginosis: the “clue cells” seen on microscopy are vaginal epithelial cells coated with bacteria, Gardnerella among them.
Yet Gardnerella is also carried by a substantial share of healthy, symptom-free women. It is best understood as a common member of the vaginal microbiota that, under certain conditions, takes part in dysbiosis.
How it works
Several traits help explain its role in BV:
- Biofilms: it can attach to the epithelium and build biofilms that other anaerobes join. These are thought to contribute to persistence and recurrence.
- Enzymes and toxins: some strains produce sialidases and the cytotoxin vaginolysin, which have been linked to mucus breakdown and cell damage.
- Strain diversity: not every strain carries the same virulence factors.
That diversity has a taxonomic basis. Vaneechoutte and colleagues (International Journal of Systematic and Evolutionary Microbiology, 2019) analysed 81 genomes, identified 13 genomic species within the genus and named three new species alongside G. vaginalis: G. leopoldii, G. piotii and G. swidsinskii. One practical consequence: their 16S rRNA genes are almost identical, so 16S rRNA gene sequencing usually cannot separate them, and many reports group them as “Gardnerella spp.”.
Example
A vaginal microbiota report from a woman without symptoms shows Gardnerella at 5% relative abundance within an L. crispatus-dominated community. That is a common finding and, in context, does not suggest BV. In a second patient with discharge and odour, Gardnerella makes up 45% of reads alongside other anaerobes, with very few lactobacilli. That profile is consistent with BV, which the clinician confirms with Amsel criteria or a Gram stain scored by the Nugent method. The percentages are illustrative; there is no universal cut-off.
Limitations
- Detecting Gardnerella on its own has little diagnostic value.
- 16S-based methods have limited resolution within the genus.
- Relative abundance depends on the rest of the community and on the method used.
Gardnerella at Xenogene
Xenogene’s AMC Vaginal profiles the vaginal ecosystem by NGS. According to the product sheet, Gardnerella is among the dysbiosis-associated species it reports, together with Atopobium and Prevotella, the dominant lactobacilli and diversity indices. Results are read in the context of the whole community and the clinical picture, and that interpretation is the responsibility of the healthcare professional who orders the test.
Frequently asked questions
Does Gardnerella on a swab mean I have an infection?
Not necessarily. Gardnerella is part of the vaginal microbiota of many healthy women. What points to bacterial vaginosis is the overall picture: symptoms, pH, clue cells, loss of lactobacilli and the share of anaerobes. A clinician needs to assess it.
Is Gardnerella sexually transmitted?
It has been found in male sexual partners and BV is linked to sexual activity, but Gardnerella is not considered a classic STI and also occurs in women who have never had sex. The role of partners in recurrence is still being studied.
Should Gardnerella be treated if there are no symptoms?
Generally, finding Gardnerella without symptoms or a BV diagnosis is not routinely treated, although a clinician may consider it in specific situations. The decision rests with the professional caring for the patient.
Related terms
- Bacterial vaginosis
Bacterial vaginosis is a shift in the vaginal microbiota in which lactobacilli decline and anaerobic bacteria such as Gardnerella overgrow. It can cause discharge and odour, but is often symptom-free.
- Vaginal microbiota
The vaginal microbiota is the community of microorganisms living in the vagina. In many women of reproductive age it is dominated by Lactobacillus species, which produce lactic acid and help keep vaginal pH low.
- Lactobacillus
Lactobacillus is a genus of Gram-positive, lactic acid-producing bacteria. Species such as L. crispatus, L. gasseri, L. iners and L. jensenii commonly dominate the vaginal microbiota of women of reproductive age.
- Relative abundance
Relative abundance is the share of a microorganism in the total detected in a sample, usually given as a percentage. It reflects its weight within the community, not its absolute quantity.
Educational content for healthcare professionals and the general public. It does not replace assessment by a healthcare professional: ordering and interpreting any test is the responsibility of the requesting clinician.
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