Mycoplasma Genitalium Mgen

Authored by , Reviewed by Shalini Patni | Last edited | Certified by The Information Standard

Mycoplasma genitalium (also called Mgen and sometimes seen as M. genitalium) is a sexually transmitted infection caused by a germ (bacterium). Mycoplasma genitalium transmission can occur it if you have sex with a person who already has the infection.

Mgen is more common in young people and in people who do not use condoms during sex. It is often asymptomatic but it can cause serious health problems if left untreated. There are concerns that Mgen has the potential to become a 'superbug', which means a bacterium which is resistant to available antibiotic treatments.

Mycoplasma genitalium (Mgen) is a sexually transmitted infection (STI) which causes few, and often no, symptoms. It is sometimes described as a 'new' STI but it was, in fact, discovered in 1981. At that time it was unclear that it was sexually transmitted, and no reliable test had been developed to detect it. A reliable test that hospital labs can use has only been available since 2017.

Mgen is caused by a tiny bacterium called Mycobacterium genitalium. It infects the urogenital tract, which means the vagina, womb (uterus) and Fallopian tubes and urethra in women, and the urethra and epididymis (sperm-carrying tube) in men.

To read more about other STIs, see the separate leaflet called Sexually Transmitted Infections.

Mgen is thought to infect 1 to 2 in every 100 adults aged 16-44 years in the UK who are sexually active. However, relatively few studies, to date, have looked at how common this infection is. Some experts think Mgen may already infect around 2% of Europeans and 3% of the world's population. 

Infection rate is highest in those who have multiple sexual partners or do not practise safe sex (this is true for all STIs). It is also more common in those who smoke (which we know makes people more susceptible to many infections) and those of non-white ethnicity (possibly for reasons of inherited differences in the immune system). 

Mgen infection has very similar symptoms to infection with chlamydia, but it is caused by a different germ (bacterium). Many cases in the past have probably been treated as if they were chlamydia, and this may have led to Mgen 'learning' about antibiotics and developing resistance, since treatment for chlamydia does not completely eradicate Mgen.

It is possible to have both infections. Mgen appears to be less common than chlamydia. It also appears to be slightly less easily transmitted than chlamydia.

See the separate leaflet called Chlamydia for more information. 

Urethritis is inflammation of the urethra, which is the tube that carries urine out from the bladder. Urethritis is most commonly caused by infection and is the most common condition diagnosed and treated among men in genitourinary medicine (GUM) clinics or sexual health clinics in the UK.

Urethritis is known to be an STI. Some years ago, when testing was not available for chlamydia or for Mgen (and they were not known as major causes of urethritis), cases of urethritis were divided into two terms. They were referred to as 'gonococcal urethritis' and 'non-gonococcal urethritis' (NGU) - sometimes also called 'nonspecific urethritis' (NSU).

When a test for chlamydia was developed it became clear that many, but not all, cases of NGU were due to chlamydia. However, significant numbers of cases did not test positive for either gonococcus or chlamydia. It now seems likely that many - if not most - of these are due to Mgen.

The most common causes of NGU is still chlamydia, although in the UK Mgen is now believed to be more common than gonorrhoea.

To read more about these infections, see the separate leaflets called Gonorrhoea, Urethritis and Urethral Discharge in Men and Non-gonococcal Urethritis.

Mgen is caught from sex with an infected person. It is transmitted through genital to genital contact such as vaginal or anal sex. This may occur even without penetration.

Can I catch Mycoplasma genitalium from oral sex?

It is not yet clear whether it can be easily transmitted through oral sex, but it is thought possible.

Will a condom protect me from Mycoplasma genitalium?

Yes, whilst condoms do not provide perfect protection, male or female condom use provides a very high level of protection against Mgen since it greatly reduces direct contact between genital tissues, particularly the penis.

The infection most often has no symptoms. It is thought that 7-8 out of every 10 affected men, and half to three quarters of affected women do not have symptoms.

However, in male patients with nongonococcal urethritis and female patients with pelvic inflammatory disease Mgen is a common cause.

Where Mgen causes symptoms, they are thought to typically appear 1-3 weeks after initial infection. They include:


  • Urethritis (inflammation and swelling of the tube that carries urine from the bladder to outside).
  • Pain on passing water.
  • Pain on ejaculation.
  • Watery or cloudy discharge from the tip of the penis.
  • Inflammation of the back passage (proctitis).
  • Inflammation of the foreskin and penis.


  • Urethritis (causes pain on urination, soreness in the external genitalia).
  • Increased or altered vaginal discharge.
  • Bleeding between periods.
  • Cervicitis (inflammation of the cervix) causing pain on intercourse and discharge or bleeding after intercourse.
  • Lower tummy (abdominal) pain.

The complications of Mgen infection result mainly from the way the immune system reacts to the germ (bacterium). An exception to this, however, is that the bacterium itself appears to be directly harmful to the Fallopian tube lining. The main complications are similar to those of chlamydia;

  • Pelvic inflammatory disease: this is infection and inflammation in the womb (uterus)  and Fallopian tubes. It occurs in women. Symptoms may include abdominal pain and pain on intercourse, a raised temperature, and becoming significantly unwell. Infection of the Fallopian tubes may cause them to become scarred and blocked, leading to tubal infertility.
  • Sexually acquired reactive arthritis (SARA) can occur as a reaction to urethritis in men and women.
  • Epididymo-orchitis may occur in men - this is painful swelling and infection of the testicle (testis) and a tube called the epididymis. There has been a suggestion that Mgen may have a role in male infertility. This has not yet been proved.
  • If someone has other STIs like HIV, having Mgen as well makes them more likely to pass on those other infections. 

Mgen is linked to preterm birth and miscarriage.

It is thought possible that Mgen can be passed to your baby at the time of vaginal delivery. It is not clear whether Mgen can be passed to your baby whilst in the womb (uterus) and it is also unclear whether this would harm your baby.

If you are diagnosed with Mgen and you are pregnant, you should inform your midwife and obstetrician. It is also vitally important that you inform the clinic which is treating your Mgen if you are or may be pregnant, since not all antibiotics used for Mgen are safe for use in pregnancy.

You can't tell whether your partner has Mgen - they too may not know, since the infection normally causes no symptoms (it is asymptomatic).

Mgen can be detected by laboratory tests performed on vaginal swabs (from women) and 'first void' urine samples from men. In transgender and non-binary patients the type sexual activity they have engaged in will determine the most suitable swab.

The germ (bacterium) is not easy to detect or isolate, and a special test called a nucleic acid detection test is used.

Laboratories also test Mgen for antibiotic resistance in order to determine which treatment to use.

People who should be tested for Mgen

Tests should be performed for:

  • Any men or women with symptoms that could be due to Mgen.
  • All men with non-gonococcal urethritis.
  • All women with pelvic inflammatory disease.
  • Current sexual partners of persons infected with Mgen.

Sexual partners who test positive but have no symptoms should be treated for Mgen. It is not yet clear if Mgen is harmful to them, but treating them prevents them from passing Mgen back to the affected patient or on to others.

The treatment for Mgen is changing, as the germ (bacterium) is rapidly becoming resistant to the usual treatments. The mainstay of treatment used to be a single dose of an antibiotic, azithromycin. However, longer courses of treatment are needed.

Newer medicines like pristinamycin, solithromycin, and sitafloxacin are being tried. However, widespread use of these newer medicines - particularly if patients don't complete the course, so that their Mgen is not completely eradicated - will lead to further drug resistance.

Current sexual partners should be given the same treatment regime as the patient.

Current recommended treatments in the UK

  • Doxycycline 100 mg twice daily for seven days; or
  • Azithromycin 1 g as a single dose, then 500 mg daily for two more days; or
  • Moxifloxacin 400 mg daily for 10 days. This is currently reserved for cases known to be resistant to azithromycin. Resistance to moxifloxacin is already problematic in Asia.

If these are not effective, alternatives are:

  • Doxycycline 100 mg twice daily for seven days, followed by pristinamycin 1 g four times daily for 10 days.
  • Pristinamycin 1 g four times daily for 10 days.
  • Doxycycline 100 mg twice daily for 14 days.
  • Minocycline 100 mg twice daily for 14 days.

In cases of pelvic inflammatory disease and epididymo-orchitis it is recommended that a 14 day course of moxifloxacin (400 mg once daily) be used. 

It is recommended that a repeat test be done three weeks after finishing treatment, to make sure the infection has completely gone. One of the main causes of medication resistance is partial treatment of infections. If infections are partly treated, a few bacteria remain - the ones that were slightly better at resisting the antibiotic; these bacteria develop a resistance mechanism which is then passed on as they multiply.

It is highly unlikely that Mgen ever goes by itself.

Although our immune systems are very good at fighting off some kinds of germs (bacteria), we seem to be less good at eradicating the group called mycobacteria. These organisms are very hardy, can often infect us without causing any detectable illness, and hide inside the cells of our bodies in order to avoid attack by our immune systems.

You should refrain from intercourse until you and your partner have completely finished treatment. Women with pelvic inflammatory disease should refrain from intercourse until 14 days after the start of treatment or 14 days after symptoms have resolved, whichever is later. 

Scientists are still learning about Mgen. At present, if you are diagnosed with Mgen, doctors have no means of determining when you caught it. It seems likely that, once you have caught it, the infection will remain until it is treated. Most courses of antibiotics that you might have had, such as those generally used for tonsillitis or cystitis, would not have eradicated the bug.

It is also not known whether people who have symptoms from Mgen could previously have had silent infections.

This means that a diagnosis of Mgen does not mean that you have acquired the bug recently; you may have had it for a long time. 

Mgen is transmitted by genital-to-genital contact. You can therefore acquire it without having full intercourse. It is an STI, so transmission requires sexually intimate contact.

Yes, you can. Mgen is transmitted by genital-to-genital contact including vaginal and anal contact and oral-to-genital contact. It is likely to be more easily transmitted in cases of genital contact, by men with symptoms of urethritis, and by women with symptoms of urethritis of pelvic inflammatory disease. 

Because Mgen appears to particularly infect the urethra in men and women, male or female condom use will greatly reduce transmission between couples of any gender.

If Mgen is eradicated with antibiotics then, as long as you have not already developed complications, there is no reason to think it will cause any long-term health problems.

If (as we suspect) Mgen causes tubal damage in patients who develop pelvic inflammatory disease, then this could result in irreversible tubal damage which could affect your fertility.

It is unclear whether Mgen can cause infertility in men who develop epididymo-orchitis - this is possible but research is ongoing.

If reactive arthritis develops as a consequence of Mgen then it is likely that, as for chlamydia, treatment of the Mgen will treat the arthritis, although it typically takes a few months to settle down.

At present doctors do not recommend that we test everyone for Mgen. This would involve testing millions of people in order to detect the 1 in 100 people who are thought to be positive.

This is not done because:

  • It would be a hugely costly exercise, in money and manpower.
  • It appears likely that it is patients who have symptoms of pelvic inflammatory disease who are at risk of complications from Mgen.
  • Treatment is currently not perfect, and if we try to treat everyone then the rate at which the bacterium becomes resistant to known antibiotics will also increase rapidly.
  • It is better therefore to refrain from treating everyone until it is clear that we can treat them effectively, without causing more resistance, and to save treatment for those we think are at risk of complications. We otherwise risk making it impossible to treat anyone.  

You will be tested for Mgen if you develop suggestive symptoms, or if your partner develops symptoms and tests positive, or if you have any other reason to be concerned you might have contracted Mgen. You will also be tested if you develop symptoms of, or are diagnosed with, another STI.

Mgen testing 'on demand' if you have no symptoms and are not thought to be at risk may become available over time.

The fewer sexual partners you have, the less likely you are to contract this infection.

Wearing a condom will help protect you against Mgen, and will prevent most cases of transmission.

If you are a smoker, you can also reduce your chances of catching mycoplasma, and other STIs, if you quit smoking.

If you are in a monogamous relationship, you may be wondering whether to stop using condoms. This may be because you want to conceive, or because you would like not to bother with condoms any more, or because you want to express your trust and commitment in this way.

If either or both of you have had sexual partners in the past, then it is not impossible that you have a 'silent' STI such as Mgen or chlamydia.

It is therefore sensible to have tests done before you make this commitment. This is particularly important if

  • Either of you has symptoms of Mgen, or any other sexually transmitted condition.
  • You have had symptoms in the past but they seem to have settled down without treatment.
  • You know or suspect that a previous partner has required treatment for an STI.

Seek advice from your local sexual health clinic or GUM clinic about testing. Before doing so consider:

  • Can you and your partner talk about this? It is a sensitive topic but if you can't talk about it, you probably shouldn't be doing it. Consider it not as showing mistrust in each other but showing proper concern for each other. 
  • This is an important next step in a relationship, but you should only do it if both of you feel comfortable.
  • Are you both committed to monogamy? If you are not sure that this is true of you, or you are not sure that you feel certain of your partner, then getting tested now only offers temporary reassurance.
  • If you are not planning to start a family, have you thought about birth control? If you are planning to have a baby together it is particularly important to know that you're healthy - for your sake and for your baby's sake.
  • Most GUM and sexual health clinics allow you to make appointments and offer single-gender clinics, and also offer drop-in clinics where you can turn up without an appointment. They will talk to you about which tests they advise you to do.
  • Mgen testing is not yet part of a routine sexually health screen as the test is not available everywhere. This seems likely to change in the future. 

You may also find it helpful to read the separate leaflet called STI Tests.

Further reading and references

  • ; Mycoplasma genitalium infections: current treatment options and resistance issues. Infect Drug Resist. 2017 Sep 110:283-292. doi: 10.2147/IDR.S105469. eCollection 2017.

  • ; Prevalence of Mycoplasma genitalium and other sexually-transmitted pathogens among high-risk individuals in Greece. Germs. 2018 Mar 18(1):12-20. doi: 10.18683/germs.2018.1128. eCollection 2018 Mar.

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