Mycoplasma genitalium, usually shortened to Mgen or M. genitalium, is a sexually transmitted bacterium that infects the urogenital tract and ranks among the leading causes of non-gonococcal urethritis in men and cervicitis in women. Despite being identified decades ago, it remains far less well known than chlamydia or gonorrhea, and most people who carry it have no idea they’re infected. What makes Mgen particularly frustrating for clinicians is its rapidly growing resistance to the antibiotics most commonly used against it, which has turned what should be a straightforward infection into one of the trickier STIs to manage.
A Bacterium Unlike Most Others
Mgen is one of the smallest self-replicating organisms known. It has a distinctive flask-like shape and lacks a cell wall, which is an important detail because many common antibiotics, like penicillin, work by attacking bacterial cell walls. That makes those drugs useless against Mgen from the start, narrowing the treatment options before resistance even enters the picture. The organism attaches to cells lining the urogenital tract and triggers a local immune response involving inflammation and the recruitment of white blood cells called neutrophils.1Oxford University Press. The Unique Microbiology and Molecular Pathogenesis of Mycoplasma genitalium
One reason Mgen is so good at sticking around is its ability to constantly change the proteins on its surface. This extensive antigenic variation essentially lets the bacterium dodge your immune system’s memory, so even after your body mounts a response, the infection can persist for months or longer. That capacity for immune evasion helps explain why untreated Mgen infections can quietly linger, causing low-grade inflammation without obvious symptoms.
How Common Is Mgen?
In the general population of higher-income countries, roughly one to two percent of people carry Mgen at any given time. In lower-income countries, prevalence is higher, around four percent. These figures come from randomly selected community samples, so they represent ordinary adults who aren’t necessarily seeking care for any symptoms. Rates are similar in women and men.2Sexually Transmitted Infections. Prevalence of Mycoplasma genitalium in different population groups: systematic review and meta-analysis
Among people attending sexual health clinics, the numbers jump. In populations at higher risk, such as men who have sex with men (MSM) or sex workers, positivity rates are substantially higher. One study of MSM in Zurich found that about one in five participants tested positive for Mgen at least once during the study period, with an incidence rate of roughly 20 new infections per 100 person-years.3PubMed Central. High Rates of Asymptomatic Mycoplasma genitalium Infections With High Proportion of Genotypic Resistance to First-Line Macrolide Treatment Among Men Who Have Sex With Men Enrolled in the Zurich Primary HIV Infection Study Among informal female sex workers in South Africa, over a quarter had at least one STI detected, with Mgen among the pathogens found at genital, rectal, and oral sites.4PubMed. Prevalence of four sexually transmitted pathogens and risk factors related to oral, vaginal, or anal intercourse among informal female sex workers from Tshwane, South Africa, 2022
How Mgen Spreads
Mgen is transmitted through sexual contact, primarily vaginal and anal intercourse. In modeling studies among MSM in Australia, anal sex accounted for about 82 percent of transmission events, while oral sex contributed around 18 percent. Adding kissing or rimming to the model didn’t substantially change the numbers, suggesting that penetrative sex is the dominant route.5PubMed Central. Modelling the multiple anatomical site transmission of Mycoplasma genitalium among men who have sex with men in Australia
Mgen can infect multiple anatomical sites. In the same modeling study, about 62 percent of infections were estimated to occur at the anorectum, 35 percent at the urethra, and a small fraction at the oropharynx. This multi-site picture matters because someone treated based on a urethral test alone might still carry the organism at another site, creating a reservoir for reinfection or onward transmission. There’s no strong evidence that Mgen spreads through casual contact like sharing towels or toilet seats.
Symptoms in Men
Mgen is recognized as one of the major causes of non-gonococcal urethritis (NGU) worldwide.6PubMed Central. Mycoplasma genitalium Infection in Men When symptoms do show up, the most common complaints are:
- Urethral discharge: usually thinner and less noticeable than gonorrhea’s thicker discharge
- Burning or stinging during urination
- Irritation at the tip of the penis
In a study of men presenting with urethritis symptoms in Turkey, Mgen was detected in about 6 percent of patients, less common than Ureaplasma urealyticum but still clinically relevant.7PubMed Central. Investigation of mycoplasma and ureaplasma species using a molecular method in male patients suffering from urethritis symptoms: a cross-sectional study in the city of Antalya Mgen has also been associated with other conditions in men including inflammation of the prostate gland and, less commonly, epididymitis.
Symptoms in Women
In women, Mgen can cause cervicitis (inflammation of the cervix), urethritis, and pelvic inflammatory disease (PID). The presentation tends to be subtler than gonorrheal infections. In a study comparing women with PID, those with Mgen were significantly less likely to have visible mucopurulent cervicitis compared to women with gonorrhea, which can make Mgen-related PID easier to miss during a clinical exam.8PubMed Central. Clinical Presentation of Mycoplasma genitalium Infection versus Neisseria gonorrhoeae Infection among Women with Pelvic Inflammatory Disease
Symptoms women might notice include unusual vaginal discharge, bleeding between periods or after sex, pelvic pain, and discomfort during urination. But many women with Mgen experience no symptoms at all, which is a pattern that carries real consequences for reproductive health.
The Reproductive Health Concern
The link between Mgen and pelvic inflammatory disease is one of the most clinically important findings about this pathogen. A systematic review and meta-analysis of 19 studies found that Mgen infection was significantly associated with PID, and that about 10 percent of women with PID tested positive for the organism.9PubMed Central. Systematic Review and Meta-analysis of the Association Between Mycoplasma genitalium and Pelvic Inflammatory Disease (PID) Earlier research suggested even stronger associations in specific contexts: one prospective study linked Mgen to over a thirteenfold increased risk of endometritis, and a post-termination study found a sixfold increased risk of PID among Mgen-positive patients.10PubMed Central. Mycoplasma genitalium: an emerging cause of pelvic inflammatory disease
PID matters because it can lead to scarring in the fallopian tubes, which in turn raises the risk of ectopic pregnancy and tubal infertility. Researchers have found elevated Mgen antibodies in women with tubal factor infertility, though whether Mgen directly causes long-term reproductive damage or acts as a contributor alongside other infections isn’t fully settled. The concern is serious enough that clinicians increasingly consider Mgen testing in women with unexplained PID, especially when chlamydia and gonorrhea tests come back negative.
Most Infections Are Silent
Perhaps the most important thing to understand about Mgen is that the majority of infections produce no symptoms at all. In the Zurich cohort of MSM mentioned earlier, 93 percent of detected Mgen infections were asymptomatic.3PubMed Central. High Rates of Asymptomatic Mycoplasma genitalium Infections With High Proportion of Genotypic Resistance to First-Line Macrolide Treatment Among Men Who Have Sex With Men Enrolled in the Zurich Primary HIV Infection Study Among asymptomatic people attending sexual health clinics, about 4.5 percent tested positive for Mgen, a rate comparable to what clinics typically find for chlamydia or gonorrhea in similar populations.11Sexually Transmitted Infections. Mycoplasma genitalium in asymptomatic patients: Implications for screening
Asymptomatic infection isn’t just a snapshot phenomenon. In heterosexual men treated for NGU with standard antibiotics, Mgen was shown to persist without symptoms for many months after treatment, meaning people can unknowingly transmit the infection to partners long after they assumed they were cured.12PubMed Central. Long Duration of Asymptomatic Mycoplasma genitalium Infection After Syndromic Treatment for Nongonococcal Urethritis Some infections do clear on their own: in the Zurich study, about 30 percent of participants showed spontaneous clearance without treatment. But relying on spontaneous resolution is a gamble, particularly for women given the association with PID.
Why Treatment Has Become So Difficult
Because Mgen has no cell wall, the antibiotic classes that target cell wall synthesis are off the table entirely. Clinicians rely on macrolides (like azithromycin) and fluoroquinolones (like moxifloxacin) as the main weapons. The problem is that resistance to both classes is rising fast.
In a study of high-risk patients in Taiwan, about 24 percent of Mgen strains carried mutations associated with macrolide resistance, 22 percent with fluoroquinolone resistance, and 8 percent with tetracycline resistance.13PubMed. Mycoplasma genitalium infection and resistance-associated mutations to macrolides and fluoroquinolones among high-risk patients in Taiwan A pilot study from India found macrolide-resistant mutations in 46 percent of Mgen strains from MSM attending an STI clinic, with about 15 percent carrying both macrolide and fluoroquinolone resistance mutations simultaneously.14Indian Journal of Dermatology, Venereology and Leprology. Macrolide and fluoroquinolone resistance associated mutations in Mycoplasma genitalium in men who have sex with men attending STI clinic: A pilot study from India Research using next-generation sequencing has identified mutations across multiple genetic loci connected to resistance in both drug classes.15PubMed Central. Detection of resistance to macrolides and fluoroquinolones in Mycoplasma genitalium by targeted next-generation sequencing
What’s alarming about some of these findings is that resistance mutations were detected even in patients who hadn’t recently taken the relevant antibiotics, suggesting that resistant strains are circulating in the community and can be acquired directly through sexual transmission rather than arising only from individual treatment failure.
Current Treatment Approaches
The gold standard for Mgen treatment is now resistance-guided therapy, meaning you test the organism for resistance mutations before choosing the antibiotic. This approach, where it’s available, produces excellent results. A large study found that a doxycycline lead-in followed by azithromycin (for macrolide-susceptible strains) achieved a cure rate of about 95 percent, while doxycycline followed by moxifloxacin (for macrolide-resistant strains) cured about 92 percent of cases.16PubMed. Resistance-Guided Antimicrobial Therapy Using Doxycycline-Moxifloxacin and Doxycycline-2.5 g Azithromycin for the Treatment of Mycoplasma genitalium Infection: Efficacy and Tolerability
The doxycycline lead-in is a key part of the strategy. Doxycycline by itself rarely cures Mgen, but it reduces the bacterial load substantially before the second-line antibiotic is introduced. This one-two punch appears to improve overall cure rates and may help reduce the chance of the surviving bacteria developing further resistance.
The problem is that resistance-guided therapy requires a test that can detect both the presence of Mgen and its resistance profile, and these tests aren’t universally available. In many settings, clinicians still have to treat empirically, often starting with azithromycin and hoping for the best. When that fails, they switch to moxifloxacin, but moxifloxacin carries more side-effect concerns and is not available everywhere globally.
When Standard Treatments Fail
For people whose Mgen doesn’t respond to either macrolide or fluoroquinolone therapy, the situation gets genuinely challenging. Several salvage strategies have emerged, including sequential regimens that use minocycline as a lead-in followed by another drug class, combination regimens that hit the organism with two antibiotics simultaneously, repurposed antibiotics like pristinamycin or spectinomycin, and newer agents like gepotidacin that work through different mechanisms.17Open Forum Infectious Diseases. Treatment Approaches for Refractory Mycoplasma genitalium Infection
Pristinamycin, an older antibiotic that requires multiple daily doses over 10 days or more, has shown promise in salvage scenarios but remains difficult to source in many countries. Gepotidacin, a novel triazaacenaphthylene antibiotic, works through a different mechanism than existing drugs and is being watched closely as a potential game-changer if it reaches widespread approval.18PubMed Central. Mycoplasma genitalium infections: current treatment options and resistance issues Experts stress the urgent need for new antimicrobial classes and coordinated global surveillance to keep pace with Mgen’s resistance evolution.19PubMed. Mycoplasma Genitalium – Where are we at?
Should You Get Screened?
Here’s a point that often surprises people: despite Mgen’s prevalence and potential for harm, the CDC does not currently recommend routine screening for it. The rationale is complex. Widespread screening would catch many asymptomatic infections, and treating all of those with antibiotics could accelerate resistance development across the population, potentially making Mgen harder to treat for the people who actually develop symptoms or complications.
The rise of multiplex testing panels, which bundle Mgen alongside chlamydia and gonorrhea on a single test, has created something of a clinical headache. An analysis of STD consultation trends found a surge in Mgen-related clinical questions following the adoption of these bundled tests, suggesting that the technology was driving diagnoses of an infection clinicians weren’t necessarily looking for and didn’t always know how to manage.20Open Forum Infectious Diseases. Trends and Themes in Mycoplasma genitalium Consultations Received Through the Sexually Transmitted Diseases Clinical Consultation Network 2015–2024 Mgen testing is currently recommended when someone has symptoms of urethritis, cervicitis, or PID, especially when tests for chlamydia and gonorrhea are negative. It’s also reasonable in the context of partner notification when a sexual partner has been diagnosed.
Diagnostic Barriers in Resource-Limited Settings
Mgen diagnosis requires molecular testing, specifically a nucleic acid amplification test (NAAT). Culture is technically possible but impractical because the organism grows extremely slowly and requires specialized media that most labs don’t maintain. This means that in settings without access to molecular diagnostics, Mgen effectively can’t be diagnosed at all.
In much of the world, sexually transmitted infections are still managed using a syndromic approach, where treatment is based on symptoms rather than laboratory results. Mgen fits poorly into that framework: its symptoms overlap with chlamydia and gonorrhea, and the standard syndromic treatments (which often involve azithromycin as a single dose) are increasingly insufficient against Mgen. Reviews of STI diagnostic capacity in resource-constrained settings have highlighted the need for affordable point-of-care molecular tests as a critical gap, one that affects Mgen diagnosis particularly because there is simply no cheaper alternative to molecular detection.21PubMed Central. Diagnosing sexually transmitted infections in resource-constrained settings: challenges and ways forward
This diagnostic gap has real consequences. A person in a setting without Mgen testing who develops urethritis may receive azithromycin monotherapy, which has a declining cure rate for Mgen and could actively select for resistant strains. They leave the clinic thinking they’ve been treated, but the infection may persist asymptomatically, continuing to spread.
Mgen and HIV Risk
There’s an evolving picture around Mgen and its relationship to HIV. Some research has found that MSM with rectal coinfections of gonorrhea and Mgen were roughly three times more likely to be HIV-positive compared to those with gonorrhea alone.22Sexually Transmitted Infections. Extragenital Mycoplasma genitalium infections among men who have sex with men A cohort study of young sexual and gender minorities found that testing positive for rectal Mgen was initially associated with about a threefold increased odds of HIV seroconversion, though this association lost statistical significance after adjusting for sexual behavior and demographic factors.23Open Forum Infectious Diseases. Asymptomatic Rectal Bacterial Pathogens Show Large Prospective Relationships With HIV Incidence in a Cohort of Young Sexual and Gender Minorities: Implications for STI Screening and HIV Prevention
The picture is clearer for rectal gonorrhea than for Mgen specifically when it comes to predicting HIV acquisition. Still, the biological rationale for concern makes sense: any infection that causes rectal or genital inflammation disrupts mucosal barriers and recruits immune cells that HIV targets. Whether treating Mgen would independently reduce HIV risk remains an open question, but the co-occurrence of these infections in high-risk populations underscores the importance of comprehensive STI care.
Partner Notification and Practical Considerations
When someone is diagnosed with Mgen, their recent sexual partners need to be tested and, if positive, treated. Given the high rates of asymptomatic infection, simply asking partners whether they have symptoms isn’t sufficient. Current UK guidelines recommend that all sexual contacts within the appropriate window be notified and offered testing.24PubMed Central. British Association of Sexual Health and HIV National guideline for the management of infection with Mycoplasma genitalium, 2025
Practically speaking, you should avoid sexual contact until both you and your partner have completed treatment and a test of cure confirms clearance. A test of cure is typically performed at least three weeks after finishing antibiotics, because testing too early can detect dead bacterial DNA and produce a misleading positive result. If your test of cure comes back positive, retreatment with a different regimen is needed, ideally guided by resistance testing. Reinfection from an untreated partner is one of the most common reasons for apparent treatment failure, so making sure partners are treated concurrently makes a real difference in outcomes.
What Sets Mgen Apart From Other STIs
Several features make Mgen unusual in the STI landscape. Most STIs are detectable by multiple methods; Mgen realistically requires molecular testing. Most STIs have at least two or three reliable first-line treatments; Mgen’s treatment depends increasingly on resistance profiling. And while asymptomatic carriage is common with chlamydia too, the proportion of asymptomatic infections for Mgen appears to be even higher, which means transmission networks can sustain themselves almost entirely below clinical radar.
Mgen also replicates slowly compared to most bacteria, with a doubling time measured in hours rather than minutes. This slow growth makes culture-based diagnosis impractical and may also explain why antibiotic courses need to be longer than for some other STIs. A single dose of azithromycin, which works well enough for chlamydia, is increasingly seen as inadequate for Mgen and may even promote resistance by exposing the organism to sub-lethal drug levels during its extended replication cycle.
For anyone who has been told they have Mgen, the trajectory can feel more complicated than expected for a bacterial infection. Resistance testing, potential treatment failures, repeat visits, and coordination with partners all add up. The good news is that the vast majority of infections are curable with the right antibiotic strategy, and the research pipeline includes promising new drugs. The frustrating reality is that access to the testing and drugs needed for optimal treatment remains uneven across countries and healthcare systems.