Why do these two bacteria share a name?
Both belong to the Mycoplasma genus, a group of very small bacteria that lack a cell wall. That's why they don't respond to some common antibiotics such as penicillin. Beyond that shared family, 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. 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 BASHH now recognises it 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 it's so often silent, some people test without symptoms as part of a wider screen. Others test because of urethritis, cervicitis or pelvic pain, or because a partner has been diagnosed.
What does Mycoplasma hominis do?
Most of the time, very little. It's frequently found in the genital tract of people with no symptoms, and it's not usually included in an STI screen. It has occasionally been associated with bacterial vaginosis or, less commonly, with infections in specific clinical situations such as pregnancy complications or after certain procedures. It isn't treated as a standard sexually transmitted infection the way genitalium is. When a doctor does want to look for it, that's usually because of a particular clinical picture rather than routine screening.
How are the two told apart?
Only a laboratory test that identifies the species can tell them apart, because they look the same clinically and symptoms alone can't separate them. An old test report, or a test from elsewhere, may just say "Mycoplasma" without naming the species, which is part of why the confusion is so common. If a result mentions Mycoplasma without saying which one, ask your clinician which was actually tested. When you book, it's worth confirming that Mycoplasma genitalium is specifically included, since that's the one with established treatment. Our wider Mycoplasma guide covers the genitalium infection in more depth.
Mycoplasma genitalium compared with Mycoplasma hominis:
Does a standard STI screen test for Mycoplasma?
A basic four-infection screen for chlamydia, gonorrhoea, HIV and syphilis covers those four only. Mycoplasma genitalium is added from the Silver package upward (£325 for men, £375 for women), along with Ureaplasma, Gardnerella and herpes. You can also book the Mycoplasma test on its own.
It's worth testing for Mycoplasma genitalium if urethritis symptoms carry on after treatment for chlamydia or gonorrhoea, or after those tests have come back negative. 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?
It's treated with antibiotics chosen for that specific infection, often a longer or combined course. That's because the treatment used for chlamydia doesn't reliably clear it, 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 be tested and treated too where appropriate, since it passes on through sexual contact like other bacterial STIs.
How testing works at our Harley Street clinic
The test uses a single urine sample or swab. Try not to pass urine for around 2 hours before the sample is taken, so the result is accurate. You can book it on its own, or as part of the Silver package and above if you'd like it alongside a wider screen. Walk-in appointments are available seven days a week at 117a Harley Street, or you can book ahead online. You can also read how private STI testing in London works before you come.
Book a Mycoplasma test at 117a Harley Street: £120.63 for Mycoplasma genitalium, or £156.25 combined with Ureaplasma.
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)
