Overview
Mycoplasma genitalium is a sexually transmitted bacterium that has moved, over the past two decades, from a research curiosity to a recognized cause of genital tract disease. It is now included in U.S. STI treatment guidelines.[1] It is spread through direct mucosal contact, frequently causes no symptoms, and is often missed because it cannot be detected with routine tests.[2]
Two features make it clinically important. It causes a meaningful share of urethritis and cervicitis that tests negative for chlamydia and gonorrhea. It has also developed antibiotic resistance at a striking pace, which makes accurate diagnosis and resistance-guided treatment increasingly important.
It is not the same as Ureaplasma or Mycoplasma hominis. Those are close relatives that are commonly carried without causing disease, and guidelines advise against routinely testing for them.
Classification
- Phylum: Mycoplasmatota (historically Tenericutes)
- Family: Mycoplasmataceae
- Genus: Mycoplasma
- Species: M. genitalium
M. genitalium was first identified in the early 1980s. It is a relative of Mycoplasma pneumoniae, a common cause of respiratory infection. Like all mycoplasmas, it lacks a cell wall, and it has one of the smallest genomes of any self-replicating organism.[3]
Key Characteristics
- No cell wall. Beta-lactam antibiotics such as penicillin have no effect, which narrows the treatment options.
- Slow growth and hard to culture. Culture can take weeks or months. Detection relies on nucleic acid amplification tests (NAATs).[3]
- Adhesion and motility. It attaches to and glides across epithelial cells using a specialized tip structure, which helps it colonize the urogenital tract.[3]
- Frequent silent infection. Many infections produce no symptoms, which allows ongoing transmission.[2]
Health Significance
In men
M. genitalium contributes to an estimated 10–35% of non-chlamydial, non-gonococcal urethritis in men. Symptoms typically include burning on urination and urethral discharge.[2] It has also been linked to balanoposthitis, chronic prostatitis, and acute epididymitis.[3]
In women
In women, M. genitalium is associated with cervicitis and pelvic inflammatory disease (PID). Symptoms can include vaginal discharge, burning on urination, and, with PID, pelvic pain and pain during sex.[2] A meta-analysis quantified the associations with reproductive tract outcomes:[4]
| Outcome | Pooled odds ratio (95% CI) |
|---|---|
| Cervicitis | 1.66 (1.35–2.04) |
| Pelvic inflammatory disease | 2.14 (1.31–3.49) |
| Preterm birth | 1.89 (1.25–2.85) |
| Spontaneous abortion | 1.82 (1.10–3.03) |
| Infertility | 2.43 (0.93–6.34) |
The association with infertility did not reach statistical significance in the main analysis, although all associations were stronger once coinfections were accounted for.[4]
Antibiotic Resistance: The Defining Problem
M. genitalium acquires resistance quickly. A systematic review of 59 studies from 21 countries found that mutations associated with macrolide resistance were present in 35.5% of samples overall. Prevalence rose from 10.0% before 2010 to 51.4% in 2016–2017.[5] Resistance to fluoroquinolones such as moxifloxacin, the main second-line option, is also rising.[2]
This is why guidelines emphasize that diagnosis should include testing for macrolide resistance mutations where available.[2]
Testing and Treatment
Who should be tested. Testing is aimed at people with symptoms. CDC's 2021 guidelines do not recommend screening for asymptomatic M. genitalium infection in men or women.[1]
How treatment works. Treatment is typically sequential. Doxycycline is given first; on its own it cures only about 30–40% of infections, but it lowers the bacterial load and may reduce the chance of selecting for macrolide resistance.[2] It is followed by a second antibiotic chosen by resistance status:[1]
- Macrolide-sensitive strain: doxycycline followed by azithromycin. Azithromycin cures about 85–95% of macrolide-susceptible infections.[2]
- Macrolide-resistant strain, or no resistance testing available: doxycycline followed by moxifloxacin.
A test of cure and partner evaluation may be recommended. Treatment decisions belong with a clinician; incomplete or mismatched courses can drive further resistance.
How It Differs From Other Genital Infections
Symptoms of M. genitalium overlap with Chlamydia trachomatis and Neisseria gonorrhoeae infections, as well as with vaginal conditions such as bacterial vaginosis. Because these conditions require different treatments, testing — not symptoms alone — determines the cause. For the broader context of vaginal and urinary health, see our women's vaginal and urinary health protocol.
When to See a Clinician
Seek evaluation for urethral or abnormal vaginal discharge, burning with urination, pelvic pain, pain during sex, or bleeding after sex. It is especially important if symptoms persist or return after treatment for chlamydia or gonorrhea. Tell your clinician if a partner has been diagnosed with M. genitalium.
This page is for educational purposes and is not medical advice. Diagnosis and treatment of sexually transmitted infections should be guided by a qualified healthcare provider.