References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
Mycoplasma genitalium (Mgen) is a sexually transmitted bacterial infection that has become increasingly recognised over the last two decades. It can cause urethritis, cervicitis and pelvic inflammatory disease, though many people have no symptoms. What makes Mgen particularly important is the rapid rise of antibiotic resistance, which has changed how it is treated.
Here’s a practical guide.
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What Is Mgen?
Mycoplasma genitalium is one of the smallest known bacteria. It was first identified in the 1980s and has since been recognised as a significant cause of non-gonococcal urethritis in men and cervicitis in women. It’s transmitted through unprotected vaginal, anal or oral sex.
Symptoms
| In Men | In Women |
|---|---|
| Discharge from the penis | Unusual vaginal discharge |
| Burning on urination | Pain during sex |
| Pain in the testicles | Bleeding between periods or after sex |
| Often asymptomatic | Pelvic pain |
| Often asymptomatic |
Many people have no symptoms, which means Mgen is often only found when other STI testing is done.
Complications
- Non-gonococcal urethritis
- Cervicitis
- Pelvic inflammatory disease (PID)
- Preterm birth risk in pregnancy
- Possible role in infertility
Testing
Mgen is diagnosed using NAAT (nucleic acid amplification test) on a urine sample, vaginal swab or rectal swab. Modern tests can also check for macrolide resistance mutations at the same time — this is important because it determines which antibiotic will work.
Treatment
Treatment depends on whether the infection is resistant to macrolides:
- No resistance: Doxycycline 100mg twice daily for 7 days, then azithromycin (1g then 500mg daily for 2 days)
- Resistance or unknown: Doxycycline 7 days, then moxifloxacin 400mg daily for 10 days
Single-dose azithromycin (the old treatment for chlamydia and Mgen) is no longer recommended because it often fails and drives resistance.
The Resistance Problem
Mgen has developed rapid resistance to macrolides globally. In the UK, resistance rates are high and climbing, which is why:
- Testing should include resistance profiling
- First-line treatment guidelines have been updated
- Test of cure is recommended
- Responsible use of antibiotics matters
Test of Cure
Unlike many STIs, a test of cure is recommended for Mgen — usually 3-5 weeks after completing antibiotics. This confirms the infection has cleared. If it hasn’t, second-line treatment is used.
Partner Treatment
Current partners should be tested and treated to prevent reinfection. Clinic staff can help with partner notification confidentially.
Read more: Can Mgen be cured? | What is chlamydia? | LGV guide
Frequently Asked Questions
Is Mgen routinely tested for?
Not in all standard STI screens. Some services test only when symptoms are present. Ask your clinic if you’re unsure.
How is Mgen treated?
With a combination of antibiotics, tailored to whether resistance is present. Test of cure confirms success.
Can Mgen cause infertility?
It can contribute to pelvic inflammatory disease, which is a cause of infertility. Prompt treatment reduces this risk.
Related reading
- Abnormal Genital Discharge and Chlamydia
- Can Mycoplasma Genitalium Be Cured?
- Can You Get Chlamydia From Kissing?
- Can You Have Chlamydia and Test Negative?
- Chlamydia and Gay Men: What to Know
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
