Why do these two bacteria share a name?
Mycoplasma hominis and Mycoplasma genitalium both belong to the Mycoplasma genus, a group of very small bacteria that lack a cell wall, which is why they don't respond to some common antibiotics such as penicillin. Beyond that shared classification, they behave quite differently in the body. Mycoplasma genitalium was only identified in the 1980s and has since been established as a genuine cause of infection, while Mycoplasma hominis has long been recognised as something that can be present without causing any disease at all.
Is Mycoplasma genitalium an STI?
Yes. Mycoplasma genitalium is passed on through sexual contact and is now recognised by BASHH as a significant cause of urethritis in men and cervicitis in women. It can cause discharge, burning or stinging when urinating, and pain during sex, though many infections cause no symptoms at all. Left untreated, it has been linked to pelvic inflammatory disease and epididymitis. Because many infections cause no symptoms, some people test without symptoms as part of a wider screen, while others test because of symptoms such as urethritis, cervicitis or pelvic pain, or because a partner has been diagnosed.
Is Mycoplasma hominis something I need to worry about?
Usually not. Mycoplasma hominis is frequently found in the genital tract of people without any symptoms, and it is not usually included in an STI screen. It has occasionally been associated with conditions such as bacterial vaginosis or, less commonly, infections in specific clinical situations like pregnancy complications or after certain procedures, but it isn't treated as a standard sexually transmitted infection in the way genitalium is. If a doctor does want to investigate it specifically, that is usually because of a particular clinical picture, not routine screening.
How are the two told apart?
They can only be told apart by a specific laboratory test that identifies the species, because they look the same clinically and cannot be distinguished by symptoms alone. A general "Mycoplasma" mention on an old test report, or a test from elsewhere, may not specify which species was checked, which is part of why confusion between the two is common; our wider Mycoplasma guide covers the genitalium infection in more depth. When you book a test, it's worth confirming that Mycoplasma genitalium is specifically included, since that is the one with an established treatment pathway.
The table below sets out the practical differences.
Mycoplasma genitalium compared with Mycoplasma hominis:
Does a standard STI screen test for Mycoplasma?
Not the basic screen. A four-infection screen covering chlamydia, gonorrhoea, HIV and syphilis does not include Mycoplasma genitalium. It is added from the Silver package upward (£325 for men, £375 for women), along with Ureaplasma, Gardnerella and herpes, or you can book the Mycoplasma test on its own. If you have persistent urethritis symptoms after treatment for chlamydia or gonorrhoea, or after those have come back negative, Mycoplasma genitalium is one of the next things worth ruling out. For men with urethral symptoms, our NGU/NSU check, £125, tests one urine sample for chlamydia, Mycoplasma, Ureaplasma and Trichomonas.
What happens if I test positive for Mycoplasma genitalium?
Treatment is with antibiotics chosen for that specific infection, often a longer or combined course, because Mycoplasma genitalium is not reliably cleared by the treatment used for chlamydia and resistance is common. UK guidance recommends a repeat test (test of cure) a few weeks after treatment, and your clinician will tell you when. Partners should also be tested and treated where appropriate, since it is passed on through sexual contact in the same way as other bacterial STIs.
How testing works at our Harley Street clinic
Our combined Mycoplasma test is £156 and checks for Mycoplasma genitalium and Ureaplasma from a single urine sample or swab, with results back in 3 days. You should avoid urinating for around 2 hours before the sample is taken so the result is accurate. The test is available as a standalone booking, or as part of the Silver package and above if you want it alongside a wider screen, as part of our private STI testing in London service. Walk-in appointments are available seven days a week at 117a Harley Street, or you can book ahead online.
Book a Mycoplasma test at 117a Harley Street: £156 for Mycoplasma genitalium and Ureaplasma combined, results in 3 days.
References
- Mycoplasma genitalium, British Association for Sexual Health and HIV (BASHH)
- Non-gonococcal urethritis, NICE Clinical Knowledge Summaries
- Pelvic inflammatory disease, NHS
- Sexually transmitted infections: guidance, UK Health Security Agency (UKHSA)
