[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Microbiology](https://durgical.com/en/microbiology/) › [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/) › Gardnerella vaginalis

[Microbiology](https://durgical.com/en/microbiology/) · [Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

# Gardnerella vaginalis

- Bacterium
- Gram-variable
- For completeness

A bacterium that overgrows when vaginal lactobacilli are lost and causes bacterial vaginosis: gray discharge with a fishy smell.

Updated 2026-11-01

## Key points

- Clue cells: epithelial cells coated with coccobacilli.
- Amsel: homogeneous gray discharge, pH above 4.5, positive whiff test and clue cells.
- Little inflammation and few neutrophils, unlike trichomoniasis or candidiasis.
- Treated with metronidazole or clindamycin.
- Linked to preterm birth in pregnancy.

## At a glance

**Gram**
Gram-variable

**Shape**
Pleomorphic coccobacillus

**Oxygen**
Facultative anaerobe

**Family**
Bifidobacteriaceae

**Stain**
Gram-variable; coats epithelial cells (clue cells)

## Morphology

- Small Gram-variable coccobacillus
- Forms biofilms on the vaginal epithelium
- Grows alongside other anaerobes (Prevotella, Mobiluncus, Mycoplasma hominis)

## Transmission

- Not a classic infection: an imbalance of vaginal flora
- More common with new or multiple sex partners, condomless sex and douching
- Can be shared between female partners

**Reservoir:** Human vagina (part of the flora in small numbers)

### Isolation precautions

What the care team adds to standard precautions.

- Standard

## Virulence factors

- Biofilm stuck to epithelial cells: forms clue cells and shields against antibiotics
- Displaces the lactobacilli that keep the pH acidic
- Together with anaerobes it makes amines that cause the fishy smell

## Diseases it causes

- Bacterial vaginosis [Bacterial vaginosis →](https://durgical.com/en/conditions/bacterial-vaginosis/)

## Clinical picture

- Thin, homogeneous, gray-white discharge with a fishy smell that worsens after sex
- Little inflammation and hardly any itching
- Many women have no symptoms
- In pregnancy: preterm birth, prelabor rupture of membranes and chorioamnionitis

## Diagnosis

- Amsel criteria (3 of 4): homogeneous discharge, vaginal pH above 4.5, positive KOH whiff test and clue cells on wet mount
- Nugent score on a Gram stain of the discharge
- Molecular tests when microscopy is not available

## Treatment

Nitroimidazoles (oral or vaginal metronidazole; tinidazole or secnidazole) or vaginal clindamycin. Relapses are common. Pregnant women with symptoms are treated; treating a male partner is considered after relapses.

Drug class only; doses and regimens are set by the clinician from the current guideline.

In Pharmacology:

- [Metronidazole](https://durgical.com/en/pharmacology/metronidazole/)
- [Clindamycin](https://durgical.com/en/pharmacology/clindamycin/)
- [Tinidazole](https://durgical.com/en/pharmacology/tinidazole/)

## Prevention

- Avoiding douching
- Condom use
- Treating symptoms in pregnancy

## Memory aid

"Gardnerella leaves a clue and a smell": the clue cells are the detective's evidence and the whiff test confirms the fishy odor.

## Test yourself

Think of the answer, then tap the question to see it.

## What are clue cells?

Vaginal epithelial cells coated with coccobacilli such as Gardnerella, blurring their edges.

## What are the Amsel criteria for bacterial vaginosis?

Homogeneous discharge, vaginal pH above 4.5, positive KOH whiff test and clue cells; 3 of 4 are needed.

## Which treatments are used for bacterial vaginosis?

Nitroimidazoles such as metronidazole (oral or vaginal) or vaginal clindamycin.

## Why does treating symptomatic bacterial vaginosis matter in pregnancy?

It is linked to preterm birth, prelabor rupture of membranes and chorioamnionitis.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/microbiology/gardnerella-vaginalis/)

## Related

- [Neisseria gonorrhoeae](https://durgical.com/en/microbiology/neisseria-gonorrhoeae/)

## Related conditions

- [Bacterial vaginosis](https://durgical.com/en/conditions/bacterial-vaginosis/)

## What the colours mean

**Gram-positive**
Thick peptidoglycan wall: stains purple.

**Gram-negative**
Thin wall with an outer membrane: stains pink.

**Acid-fast**
Lipid-rich wall (mycobacteria): Ziehl–Neelsen stain.

[← Back to the group: Other Gram-negative rods](https://durgical.com/en/microbiology/groups/other-gram-negative-rods/)

Educational content on microorganisms; not a treatment guide and no substitute for a health professional's advice. No doses are given.

Sources: [Bacterial Vaginosis (BV)](https://www.msdmanuals.com/professional/gynecology-and-obstetrics/vaginitis-cervicitis-and-pelvic-inflammatory-disease/bacterial-vaginosis) (MSD Manual Professional Edition, 2026); [About Bacterial Vaginosis (BV)](https://www.cdc.gov/bacterial-vaginosis/about/index.html) (CDC, 2023).

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/microbiology/gardnerella-vaginalis/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/microbiology/gardnerella-vaginalis/