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Mycoplasma Introduction

Mycoplasma Introduction


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.

What is a Mycoplasma genitalium infection?

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 Mycoplasma 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.

How common is Mycoplasma genitalium infection?

Mycoplasma genitalium 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).

Is Mycoplasma genitalium the same as chlamydia?

Mycoplasma genitalium symptoms are very similar 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 mycoplasma genitalium.

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.

How do you test for Mycoplasma genitalium?

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.

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, Mgen is now believed to be more common than gonorrhoea.

How is mycoplasma genitalium transmitted?

Mycoplasma genitalium 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 Mycoplasma genitalium since it greatly reduces direct contact between genital tissues, particularly the penis.

Mycoplasma genitalium symptoms

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.

Cervicitis (inflammation of the cervix) causing pain on intercourse and discharge or bleeding after intercourse.

Lower tummy (abdominal) pain.

What are the complications of Mycoplasma genitalium infection?

The complications of a Mycoplasma genitalium 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.

Can I tell whether my partner has Mycoplasma genitalium?

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

Mycoplasma genitalium testing - what tests are there and who should be tested?

Mycoplasma genitalium 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 Mycoplasma genitalium

Tests should be performed for:

Any men or women with symptoms that could be due to Mycoplasma genitalium.

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 Mycoplasma genitalium. 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.

Does Mycoplasma genitalium go away by itself?

It is highly unlikely that Mycoplasma genitalium 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 Mycoplasma. 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.

Can I have sex whilst being treated for Mycoplasma genitalium?

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.

How long have I had Mycoplasma genitalium?

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.

How can I avoid catching Mycoplasma genitalium?

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

Wearing a condom will help protect you against Mycoplasma genitalium, 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.