Gardnerella and BV: what it does and how to treat it

Author: Jessica Lloyd
Senior Vulvovaginal Specialist Naturopath | BHSc(N) | ISSVD, ISSWSH, BSSM, ATMS

Last reviewed: July 4, 2026

Gardnerella is the bacteria most closely tied to bacterial vaginosis (BV) – the usual culprit behind grey, runny discharge and that tell-tale fishy smell. For decades it was treated as a single species, Gardnerella vaginalis. We now know it is really a whole group of closely related species, and that turns out to matter for the way BV behaves.¹

Gardnerella moves in when the protective Lactobacillus bacteria that normally rule your vagina lose their grip. It then lays down a sticky film on the vaginal wall – a biofilm – that shields it from your own defences and from antibiotics. That biofilm is the single biggest reason BV is so good at coming back.^2–3

So what is Gardnerella?

Gardnerella vaginalis was first described by Hermann Gardner back in 1955. It is a gram-variable, facultative anaerobic bacteria – meaning it can get by with or without oxygen, and it stains awkwardly under the microscope. Its cell wall is so thin it can look either gram-positive or gram-negative, even though it is technically gram-positive.

The big update is that Gardnerella is no longer one lonely species. In 2019, researchers re-examined the genetics and split the genus into several distinct species, including G. vaginalis, G. leopoldii, G. piotii and G. swidsinskii, with a string of further genome species behind them.¹

Why should you care about Latin names? Because these species are not all equally troublesome. Some are far better at building biofilms and producing the toxins that drive symptoms, which helps explain why two people with ‘the same’ BV can have very different experiences – and why a single test result rarely tells the whole story.²

What does Gardnerella do inside the vagina?

The inside of your vagina is lined with epithelial cells – the surface layer of the mucous membrane you can actually touch. Gardnerella lives on these cells, and when conditions allow, it sticks fast and starts to build.

It does this with a small arsenal of tools. It produces vaginolysin, a toxin that punches holes in human cells, and an enzyme called sialidase that strips the protective sugar coating off your vaginal mucus.^2–3 Sialidase is a useful one to know about, because the more of it that is present, the more established the biofilm tends to be – it is a marker of BV that is dug in rather than passing through.³

By stripping that mucus and displacing your protective bacteria, Gardnerella changes the whole neighbourhood. The vaginal pH drifts upward, other disruptive bacteria such as Prevotella pile in, and the smelly by-products of all that anaerobic activity start to appear. This is why BV is best understood as a community problem, not a single-germ infection.²

The biofilm, and why BV keeps coming back

Gardnerella is the species that gets the biofilm started – it sticks to the vaginal wall first and acts as the scaffold that other bacteria then attach to.² Once that film is in place, it works like a tarpaulin over the whole colony.

That tarpaulin is the reason antibiotics so often disappoint. Metronidazole and clindamycin can knock back the free-floating bacteria, but they struggle to penetrate the biofilm properly. A few survivors hunker down, and once treatment stops they rebuild. It is why between 50 and 80 per cent of women have BV back within a year of an antibiotic course.⁴

Gardnerella can only get this foothold when your Lactobacillus community is disturbed enough to fall apart. Repeated antibiotics, run-down immunity, douching and a lack of protective bacteria elsewhere in the body can all tip the balance. The trigger varies, but the result is the same – a door left open.

Is BV sexually transmitted?

This used to be a firm ‘no’. The picture has shifted, and it is worth understanding why, because it changes what you can do about stubborn BV.

In 2025, a randomised controlled trial did something simple but overdue: it treated the male partners of women with BV, using both oral and topical antimicrobials, at the same time as the women were treated. Recurrence over three months dropped to 35 per cent in the couples where the man was treated, compared with 63 per cent when he was not.⁵ That is a large difference, and it is strong evidence that men can carry and pass back the bacteria involved.

This does not mean BV is a classic sexually transmitted infection (STI, or STD) in the way chlamydia is, and you can absolutely get BV without any sexual contact at all. But it does mean that for a woman whose BV keeps returning after sex with a regular partner, treating him too is now a reasonable conversation to have with a doctor. We have written more about the male side of BV and whether condoms help prevent it.

What this means for your vagina

A protective vaginal microbiome is dominated by Lactobacillus, and the most protective state of all is one ruled by Lactobacillus crispatus.⁶ These bacteria keep the vagina slightly acidic and make it hard for Gardnerella to gain ground. When they thin out, you get the familiar BV signs: thin grey or white discharge, a fishy odour that often sharpens after sex, and a raised vaginal pH.

It is not only about comfort. A disrupted, Gardnerella-heavy microbiome is linked to a higher risk of catching HIV and other infections, and to complications in pregnancy.⁴ That is exactly why BV is worth taking seriously rather than waiting it out, and why a thorough test that names which bacteria are present – including markers like BVAB – can be so useful.

When we look at our clients’ microbiome test results here at My Vagina, Gardnerella almost never acts alone. It turns up alongside a collapse in protective Lactobacillus and a cast of other disruptive bacteria, and it is that whole picture we work to put right at the root, rather than chasing a single name on a test result.

What actually helps

Standard first-line treatment is antibiotics, usually metronidazole or clindamycin. For a one-off bout, that is often all you need, and it is a sensible place to start. The trouble comes with BV that keeps returning, where antibiotics alone tend to win the battle and lose the war.⁴

The more promising approaches go after the things antibiotics miss: the biofilm and the missing protective bacteria. Research interest now sits squarely on disrupting that film, restoring an acidic pH, and re-seeding Lactobacillus.⁴

On the probiotic front, the strongest evidence is for live Lactobacillus crispatus applied vaginally. In one well-run trial, a L. crispatus live biotherapeutic (strain CTV-05) given after antibiotics cut BV recurrence to 30 per cent by week 12, against 45 per cent on placebo.⁷ It is not a magic bullet – it works best when the antibiotics have already cleared the active infection – but it points firmly at rebuilding the microbiome rather than just bombing it.

Another measure worth knowing about is vaginal boric acid, which has reasonable evidence as a biofilm-disrupting adjunct used alongside other treatment.⁴ Raising vaginal acidity is biologically plausible too, since a low pH holds Gardnerella back, but the evidence that lactic-acid or pH products alone clear BV is weak, so they sit better as support than as a standalone fix.⁴ A word of care with boric acid: it is for vaginal use only, never swallowed, and not used in pregnancy. We dig into the wider options in our guides to natural versus prescription BV treatments, cranberry, aloe vera for biofilms, and over-the-counter options.

Frequently asked questions

Is Gardnerella an STI or STD?

Not in the classic sense. Gardnerella is a normal vaginal bacteria that overgrows, so you can develop BV with no sexual contact at all, and it is not formally classed as a sexually transmitted infection (STI or STD). That said, sex clearly plays a part: a 2025 trial found that treating a woman’s male partner lowered her chance of BV returning, so the bacteria do appear to pass between partners.⁵

Does having Gardnerella always mean I have BV?

No. Small amounts of Gardnerella can be found in plenty of people with a perfectly protective microbiome.⁶ BV is about overgrowth and biofilm – when Gardnerella and friends take over and the Lactobacillus are pushed out. The amount and the company it keeps matter far more than its mere presence.

Why does my BV keep coming back?

Usually because of the biofilm. Antibiotics clear the loose bacteria but leave the protected film behind, and a recurrence rate of 50 to 80 per cent within a year is the predictable result.⁴ Recurring BV is a sign to look at the bigger picture – the state of your protective bacteria, your triggers, and possibly a partner.

Should my partner be treated?

For a single, easily cleared bout, not necessarily. For BV that keeps returning after sex with a regular male partner, the 2025 trial evidence suggests treating him too can meaningfully lower your chance of recurrence.⁵ It is a worthwhile conversation to have with your doctor.

Can I get rid of Gardnerella naturally?

The realistic goal is not to wipe out Gardnerella entirely – it is to rebuild a Lactobacillus-dominant environment so it can no longer dominate. That is where biofilm-disrupting and microbiome-restoring approaches come in, ideally guided by testing so you know what you are actually dealing with.^4,7

Is Gardnerella dangerous?

BV itself is not an emergency, but it is not harmless either. Beyond the discomfort and odour, an ongoing imbalance is linked to higher infection risk and pregnancy complications.⁴ Persistent or pregnancy-related symptoms are always worth a proper in-person review.

What to do next

If you are dealing with BV, the most useful first step is knowing what is actually growing. A comprehensive vaginal microbiome test shows which bacteria are present and how much protective Lactobacillus you have left to work with.

From there, our free Killing BV guides walk you through the whole approach step by step. If your BV is stubborn or recurring and you would like a hand tailored to your situation, you are welcome to book an appointment with our practitioners.

This is general information, not a substitute for personalised medical advice.