Mycoplasma genitalium

STI of the bacterium Mycoplasma genitalium

Illustration of bacterial cells representing the STI Mycoplasma genitalium infection
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Find out what we know and what we don’t about this sexually transmitted infection

What is a Mycoplasma genitalium infection?

Mycoplasma genitalium (M. genitalium or Mgen) is a poorly understood STI that causes similar symptoms to Chlamydia including vaginal pain, discharge, and abnormal bleeding between or during menstruation. It affects both men and women, but it seems that women are less likely to show symptoms than men [1]. Other species of Mycoplasma, such as M. hominis, are not regarded as pathogens.

How common is it?

Little is known about how many people might have an M. genitalium infection. Not only has the condition only recently been recognized, but it is also difficult to diagnose using traditional methods. Like with other STIs, young people and people who are sexually active are more likely to be infected. Currently, estimates state that 1-2% of the population may carry it [4]. More information is needed to provide an accurate number

What causes an M. genitalium infection and who is at risk?

Mycoplasma is a type of bacteria that can be passed between people during sexual intercourse and cause an infection. It is the smallest known bacteria that is able to replicate and is so small that it doesn’t even show up under a microscope. Another unique characteristic of this bacteria that makes it hard to diagnose and treat is that it doesn’t have cell walls. That means that common antibiotics like penicillin, which work by attacking the cell walls of a bacteria, are not effective [2].

We’ve only known about M. genitalium since the 80s and it is not very well understood due to its unique biology. What we do know is that it transmits through sex. Just like with other STIs, having unprotected sex, or having sex with new or multiple partners puts you at a higher risk of infection [1].  

What are the symptoms?

When women do show symptoms of M. genitalium, they often experience [1,3]:

  • Vaginal pain during sex or while urinating 
  • Unusual or heavy bleeding between periods

How is it diagnosed?

M. genitalium can be hard to identify based on symptoms alone since they are very similar to those of other STIs. M. genitalium bacteria are very small and slow growing. This means that a culture test may take weeks and that microscopy wouldn’t detect the bacteria. Currently, the preferred method for detection is a nucleic acid amplification test (NAAT, or PCR) [3].

What are the treatment options?

The fact that M. genitalium doesn’t have cell walls means that only a small handful of antibiotics can be used to treat an infection of this bacteria. One antibiotic that does work, called Azithromycin, is unfortunately also one of the most commonly used. As a result of that widespread use, Azithromycin resistance seems to be on the rise [1]. Given this concern, it is especially important to consult your doctor before re-starting any treatment course.

Can M. genitalium lead to other complications?

Without treatment, inflammation of the vagina, cervix and endometrium caused by the infection can lead to frequent UTIs and pelvic inflammatory disease (PID), which can in turn cause fertility issues [1]. 

What can be done to prevent M. genitalium?

The best option to prevent any STI, including M. gentalium, is to practice safe sex by always discussing sexual health with your partner, using barrier protection correctly (such as a condom or dental dam), and getting tested regularly. To protect yourself against infections, avoid disrupting the balance of protective bacteria in the vaginal microbiome by limiting the use of douches as well as the use of scented soaps, tampons or pads.

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1. Emerging Issues - 2015 STD Treatment Guidelines [Internet]. 2020 [cited 17 September 2020]. Available from:

2. Long S, Prober C, Fischer M. Principles and practice of pediatric infectious diseases.

3. Mycoplasma genitalium - Q & A - 2015 STD Treatment Guidelines [Internet]. 2020 [cited 17 September 2020]. Available from:

4. New guidelines issued on the 'STI most people have never heard of' [Internet]. 2020 [cited 17 September 2020]. Available from:

Written by Aisha Ommaya, science comms officer with Juno Bio

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