Mycoplasma genitalium
The Emerging, Often-Missed, Increasingly-Resistant Cause of Urethritis
Evidence grade 4 of 5, Strong. Read how the Atlas grades evidence.
The written rationale for this grade is still being prepared.
- FDA
- NAAT assays FDA-cleared; treatment per CDC 2021 guidelines (resistance-guided)
Reference only. Not medical advice.
What can go wrong
Untreated or inadequately treated M. genitalium can cause persistent urethritis and may contribute to epididymitis; its role in male infertility is plausible but less firmly established than for chlamydia. The principal concern is antimicrobial resistance: indiscriminate azithromycin use accelerates macrolide resistance, and moxifloxacin failures are now reported. Because treatment failure is common, a test of cure is recommended, and partners should be evaluated. The lack of universal access to resistance assays in many regions complicates rational treatment.
This is something to take to a clinician. The Atlas can tell you what is known about mycoplasma genitalium in general. It cannot tell you what is happening in your body, and the difference matters most for exactly the symptoms that bring people to this page.
Mycoplasma genitalium is a small, fastidious, cell-wall-deficient bacterium increasingly recognized as a cause of non-gonococcal urethritis in men, including persistent and recurrent cases that fail standard treatment. Because it lacks a cell wall, it is intrinsically resistant to penicillins and cephalosporins, and it grows too slowly to culture routinely, so it was historically missed until nucleic acid amplification tests (NAATs) became available. The CDC's 2021 guidelines for the first time gave it a dedicated, resistance-aware treatment approach, because macrolide (azithromycin) resistance is now common and fluoroquinolone resistance is rising. Where available, macrolide-resistance testing should guide therapy.
A small, slow-growing bacterium behind a large share of stubborn, recurrent urethritis, and it is outrunning antibiotics.
What people take it for
What it is taken for. Approval, where it exists, covers only some of these.
How it works
M. genitalium adheres to and damages urethral epithelium via a specialized terminal structure, producing inflammation without the dramatic discharge typical of gonorrhea. Lacking a cell wall, it is unaffected by beta-lactams; effective drugs target protein synthesis (macrolides like azithromycin) or DNA gyrase (fluoroquinolones like moxifloxacin). Resistance is driven by mutations: 23S rRNA mutations confer macrolide resistance, and parC mutations confer fluoroquinolone resistance. The CDC 2021 strategy uses doxycycline to reduce organism load followed by azithromycin (if macrolide-susceptible) or moxifloxacin (if resistant or unknown), because sequential therapy improves cure.
Why it gets missed and why resistance is the story
Many men with M. genitalium have been treated empirically for chlamydia or non-specific urethritis and relapse, because single-dose azithromycin both fails increasingly and can select for further resistance. Routine STI panels do not always include M. genitalium, and the CDC does not recommend screening asymptomatic people; testing is reserved for symptomatic urethritis, especially persistent or recurrent disease, and for some cases of cervicitis/PID in partners. The combination of frequent macrolide resistance and emerging fluoroquinolone resistance means M. genitalium is on a trajectory similar to gonorrhea, raising concern about future untreatable cases.
What people get wrong
Often saidA standard STI panel always checks for M. genitalium
ActuallyMany panels do not include it. Testing is targeted to symptomatic, especially persistent or recurrent, urethritis rather than routine screening.
Often saidAzithromycin reliably cures it
ActuallyMacrolide resistance is now common; single-dose azithromycin increasingly fails and can worsen resistance, which is why resistance-guided sequential therapy is preferred.
Who profits, and who pushes back
Nobody is named here yet, because we have not done that work on this entry. Read that as unfinished. Somebody almost certainly sells this, and somebody almost certainly disputes it. Assume both until we have checked.
At a glance
- Cell wall
- Absent (intrinsically beta-lactam resistant)
- Main male syndrome
- Non-gonococcal/persistent urethritis
- Diagnosis
- NAAT (cannot be routinely cultured)
- Macrolide resistance
- Common and rising
- 2021 approach
- Resistance-guided therapy (doxycycline then moxifloxacin or azithromycin)
What this entry does not yet cover
What follows is unfinished work on our side, not a finding about Mycoplasma genitalium. A short entry is not a safe entry.
- Cost and market. We have not documented what it sells for or who sells it.
- Supply chain. We have not mapped where it is made.
- Who uses it. We have not documented the user groups.
- What could change. No forward-looking summary yet.
- How it compares. We have not set it against the alternatives.
- Children and teenagers. We have not checked what is known about younger people.
- Where we land. We have not taken a position on this yet.
Sources
The studies below are named and described, but not linked. You cannot open them from here and check our reading against them, which means this page is our summary of the literature rather than a document you can verify. Weigh it accordingly until the links exist.
The studies that matter
CDC STI Treatment Guidelines2021
First CDC guideline with a dedicated, resistance-guided M. genitalium regimen (doxycycline then azithromycin or moxifloxacin)
Manhart et al. and colleagues (resistance epidemiology)2010s
Documented high and rising macrolide resistance in M. genitalium across multiple populations
Read et al., Clin Infect Dis (resistance-guided therapy)2019
Resistance-guided sequential therapy improved cure rates compared with empiric azithromycin