Gardnerella vaginalis is best known as the main bacterium behind bacterial vaginosis (BV), the most common cause of unusual vaginal discharge. But it is not only a women’s bacterium. Many men carry it on the penis or in the urethra without ever noticing.1PubMed Central. Gardnerella vaginalis prostatitis and its treatment: A case report For most men, the question is less about their own health and more about whether they keep handing it back to a partner. Recent research has changed what doctors may offer male partners.2American College of Obstetricians and Gynecologists. ACOG Recommends Concurrent Sexual Partner Treatment for Recurrent Bacterial Vaginosis for the First Time
How Common Gardnerella Is in Men
Studies suggest about 7 to 11 men in 100 grow Gardnerella from genital samples, and most of them have no symptoms.3PubMed Central. Gardnerella vaginalis prostatitis and its treatment: A case report The urethra, the tube urine passes through, is a frequent silent site.4PubMed. Gardnerella vaginalis infection–another sexually transmitted disease Among men attending clinics with genital symptoms, it was the most often detected organism, found in about 1 in 5.5PubMed Central. Gardnerella vaginalis in Symptomatic Men: Prevalence, Load, and Co-infections
Gardnerella makes up nearly all of one bacterial family found on the penis that also lives in the vagina.6PubMed Central. The Effects of Circumcision on the Penis Microbiome It is not limited to the penis, either. In one clinic group of men who have sex with men, it was found in 8 of 10 rectal swabs.7PubMed Central. Gardnerella vaginalis and Mollicute detection in rectal swabs from men who have sex with men It also often appears alongside other BV-linked bacteria in the male urethra.8Malaysian Journal of Microbiology. Identification of bacterial vaginosis-associated bacteria in male urethra: Co-occurrence of Atopobium vaginae and Gardnerella vaginalis
Carrying and infection are different things. Carrying means the bacterium lives on or in you without causing harm. Infection means it is causing inflammation or symptoms. Most men fall in the first group.
That is why a positive result doesn’t mean you are sick. Many lab reports come from DNA-based panels, which can detect very small amounts of bacterial genetic material. “Detected” therefore doesn’t tell you how much is present or whether it is doing anything. Some panels report a quantity or a cutoff, and a high amount in a man with matching symptoms is more meaningful than a trace in a man with none.
Gardnerella isn’t part of the standard STI list in most clinics, so it usually turns up only when a broader panel or a symptom-driven swab is ordered. In a man with no symptoms, an incidental finding often needs no action.
How Gardnerella Passes Between Partners
Sex is the main route. A sticky, clumped form of Gardnerella was found in every woman with proven BV and in all their male partners.9PubMed. Gardnerella biofilm involves females and males and is transmitted sexually It was found in none of the healthy lab staff or children tested.10PubMed. Gardnerella biofilm involves females and males and is transmitted sexually In one couple, the same strain was traced being passed between partners over 15 years.11PubMed. Gardnerella biofilm involves females and males and is transmitted sexually So men can act as a reservoir that reinfects a partner after her treatment.
This clumped form is a community of bacteria that clump together and stick to a surface, such as the lining of the vagina or the skin of the penis, wrapped in a slimy protective layer. That layer makes the bacteria harder for antibiotics to reach and harder to wash off, so a course of pills can reduce them without fully clearing them. Leftover bacteria can rebuild the community, and because both partners can carry the same layer, treating only one person leaves a source to pass back.
The foreskin and condoms also play a part. Uncircumcised men carry denser bacteria under the foreskin, including BV-linked species.12PubMed Central. Post-coital dynamics of the penile and cervico-vaginal genital microbiome Condomless sex shifted BV-related bacteria on the penis regardless of circumcision.13PubMed Central. Post-coital dynamics of the penile and cervico-vaginal genital microbiome Women with uncircumcised partners developed BV somewhat more often, 37% versus 27%, though that difference is too small to be sure of.14PubMed Central. The Microbiome Composition of a Man’s Penis Predicts Incident Bacterial Vaginosis in His Female Sex Partner With High Accuracy
Sex isn’t the only route. Gardnerella has been found in some girls and teenagers who had never had sex.15PubMed Central. The epidemiology of bacterial vaginosis in relation to sexual behaviour All of this matters when couples start looking for someone to blame. Having Gardnerella doesn’t prove cheating, since carriage can last for years. Women can develop BV without a new partner, and same-sex couples can share it too. It’s a shared ecosystem, not one person’s fault.
Symptoms Gardnerella Can Cause in Men
Most men notice nothing. Some, though, develop inflammation of the head of the penis and foreskin linked to Gardnerella.16PubMed. Gardnerella vaginalis-associated balanoposthitis Reported signs include spread-out redness and itching around the tip and the rim of the head, an irritated foreskin, and slight discharge.17PubMed. Gardnerella vaginalis-associated balanoposthitis The discharge had a typical fishy smell.18PubMed. Gardnerella vaginalis-associated balanoposthitis
Gardnerella may also be an overlooked cause of burning or discomfort with urination in men.19PubMed Central. Gardnerella vaginalis: Is it an Underestimated Cause of Urinary Symptoms in Males? But in most men where it was found with urinary symptoms, other germs such as chlamydia were present too.20PubMed Central. Gardnerella vaginalis: Is it an Underestimated Cause of Urinary Symptoms in Males? A full STI test makes more sense than assuming Gardnerella is the cause.
Symptoms overlap with other conditions. Thrush on the penis usually shows as redness with white patches or a cheesy coating, and sometimes a yeasty smell, rather than a fishy one. A fishy smell points more toward BV-type bacteria, though smell alone can’t confirm the cause. A thicker, pus-like discharge from the urethra, often with burning on urination, is more typical of gonorrhea or chlamydia, which are more common causes and need prompt treatment. Only a swab or urine test can sort out which germ is involved, and more than one can be present at once.
At the clinic, mention if your partner has BV. Ask for a swab of the penis tip, not just a urine sample. And skip harsh soaps right before testing.
Rare Serious Infections
Gardnerella urinary infections in men are uncommon.21PubMed. Gardnerella vaginalis in urinary tract infections, are men spared? When they do occur, most reported cases spread to the blood, and some caused kidney swelling or abscesses.22PubMed. Gardnerella vaginalis in urinary tract infections, are men spared? Bloodstream infection in men is very rare and usually seen in men with weakened immunity.23PubMed Central. Gardnerella vaginalis bacteremia in a previously healthy man: case report and characterization of the isolate It has, though, occurred in a previously healthy man with kidney stones.24PubMed Central. Gardnerella vaginalis bacteremia in a previously healthy man: case report and characterization of the isolate Almost all such cases start in the urinary or genital tract.25Open Forum Infectious Diseases. Gardnerella vaginalis Bacteremia in Male Patients: A Case Series and Review of the Literature
Problems tend to happen when something gives it an opening, such as a weakened immune system, a blockage, or kidney stones that let bacteria settle in the urinary tract. A positive test in a healthy man with no symptoms is not a sign that a dangerous infection is coming.
Some signs need same-day medical care: fever with chills and pain on urinating, pain in the side or back near the kidneys, or feeling suddenly very unwell or confused.
Should Men Be Treated
For years the answer was no. Earlier trials found that treating male partners didn’t change a woman’s chance of BV coming back.26Centers for Disease Control and Prevention. Bacterial Vaginosis In one, about 3 in 10 women relapsed whether or not the partner got an antibiotic.27PubMed Central. Treatment of male partners and recurrence of bacterial vaginosis: a randomised trial CDC guidance accordingly does not recommend routine partner treatment.28Centers for Disease Control and Prevention. Bacterial Vaginosis
A 2025 trial changed the picture. Men took antibiotic pills plus an antibiotic cream on the penis.29HIVguidelines.org. Gardnerella Vaginalis in Men: Transmission, Symptoms, and Treatment BV came back in 35% of women whose partners were treated, versus 63% without partner treatment.30PubMed. Male-Partner Treatment to Prevent Recurrence of Bacterial Vaginosis The American College of Obstetricians and Gynecologists now advises considering partner treatment for adults with recurring, symptomatic BV.31American College of Obstetricians and Gynecologists. ACOG Recommends Concurrent Sexual Partner Treatment for Recurrent Bacterial Vaginosis for the First Time
The difference lies in the method. Older trials mostly gave male partners antibiotic pills alone, which treat the urethra and bloodstream but may not reach bacteria sitting on the skin. The newer approach added the cream, aimed at bacteria on the surface and under the foreskin, which is where the sticky biofilm layer appears to sit. The partners were also treated at the same time, so one was less likely to pass bacteria back to the other mid-treatment.
The usual pill is metronidazole, an antibiotic for BV-type bacteria. Avoid alcohol while taking it and for at least a day or so after, as the combination can cause severe nausea and vomiting. Ask your partner’s doctor or a sexual health clinic about a prescription.
A few practical points help. Start at the same time as your partner, since treating one person a week or two ahead leaves a window for reinfection. Avoid sex or use condoms until both courses are finished. Apply the cream exactly as prescribed, including under the foreskin if you are uncircumcised, because that is where bacteria collect. Finish the full course even if you feel fine, since you probably had no symptoms to begin with and stopping early may leave bacteria behind.
Not every man needs this. A man with no symptoms whose partner had a single BV episode usually needs nothing, because the newer guidance applies to recurring, symptomatic BV in a regular partner. If you’re unsure which situation you’re in, ask a doctor.
Why BV Keeps Coming Back
Even when both partners are treated, BV can return, and resistance is one reason. Resistance means the bacteria can survive a drug that would normally kill them, so the usual course may bring only partial or temporary relief. In women with returning BV, bacteria that were killed by metronidazole at first became resistant later.32PubMed Central. P-1274. Resistance to Metronidazole of Gardnerella in Women with Recurrent Bacterial Vaginosis In BV that never cleared, the bacteria were resistant from the start.33PubMed Central. P-1274. Resistance to Metronidazole of Gardnerella in Women with Recurrent Bacterial Vaginosis
Gardnerella can switch off a protein the drug needs to work, without any lasting genetic change.34PubMed. Downregulation of an NfsA-like nitroreductase causes metronidazole resistance in Gardnerella vaginalis Metronidazole needs that protein to become active, so if the bacteria turn it down, the drug has little effect. Because the switch isn’t a lasting genetic change, resistance can develop rapidly during repeated treatments.35PubMed. Downregulation of an NfsA-like nitroreductase causes metronidazole resistance in Gardnerella vaginalis That is one reason repeated courses of the same drug may work less well each time.
If BV keeps returning, tell the doctor how many times it has come back and how soon after each treatment, because this pattern guides the next choice. Ask whether a different antibiotic or a different way of giving it is an option, since the same drug may keep failing. Consider condoms for some months after treatment, so bacteria aren’t passed back while the vaginal bacteria recover.
The Emotional Side for Couples
Most women with recurring BV describe a moderate to severe effect on their lives.36PubMed Central. The Burden of Bacterial Vaginosis: Women’s Experience of the Physical, Emotional, Sexual and Social Impact of Living with Recurrent Bacterial Vaginosis Many feel embarrassed or “dirty” and avoid sex, especially oral sex.37PubMed Central. The Burden of Bacterial Vaginosis: Women’s Experience of the Physical, Emotional, Sexual and Social Impact of Living with Recurrent Bacterial Vaginosis Some link the shame to wider stigma around women’s sexuality and STIs.38PubMed Central. The Burden of Bacterial Vaginosis: Women’s Experience of the Physical, Emotional, Sexual and Social Impact of Living with Recurrent Bacterial Vaginosis Avoiding sex can put distance between partners even when neither has done anything wrong.
A male partner can help in practical ways. Offering to get tested or treated shows the problem is shared, not hers alone.
Talking about it helps too. Frame it as shared bacteria, not poor hygiene or cheating, so neither person feels accused. Agree together on treatment timing and on condom use during and after treatment. If it keeps recurring, go to appointments together so both of you hear the same plan. Check in on how each of you is coping, since the strain on a relationship can outlast the symptoms.