What is a Macrolide Resistance Test, and why is it bundled with a Mycoplasma Genitalium (Mgen) screen?

If you have come across the term macrolide resistance test whilst researching Mycoplasma Genitalium (Mgen), you may be wondering what it means and why it matters. Symptoms such as unusual discharge, discomfort during urination, or pelvic irritation can be unsettling, but they can have several possible causes and do not automatically indicate infection. Understanding how Mgen testing works — and why antibiotic resistance testing is now routinely included — can help you make an informed decision about your sexual health.

Our clinic provides confidential STI testing services. We do not provide GP services or dermatology consultations, but we can advise on appropriate next steps if further medical care is needed.

Quick Answer: What is a Macrolide Resistance Test?

A macrolide resistance test is a laboratory analysis performed alongside a Mycoplasma Genitalium screen. It identifies whether the detected strain of Mgen carries specific genetic mutations that make it resistant to macrolide antibiotics — the first-line treatment for this infection. Without this information, treatment may be less effective. Testing together provides a clinically complete picture.

Key points at a glance:

• Mycoplasma Genitalium is a sexually transmitted bacterial infection
• Macrolides (such as azithromycin) are the primary antibiotic used to treat Mgen
• Resistance to macrolides is rising significantly in the UK
• A resistance test identifies whether the strain will respond to standard treatment
• Results guide appropriate antibiotic selection
• Testing for resistance is now considered best clinical practice when screening for Mgen

When Could Urogenital Symptoms Be Linked to Mgen?

Symptoms such as urethral discharge, burning during urination, vaginal discharge, or pelvic discomfort can occur for a range of reasons. In some cases, these symptoms may be associated with a sexually transmitted infection such as Mycoplasma Genitalium. However, symptoms alone cannot confirm the cause. Mgen in particular is often described as a low-symptom infection — many individuals carry it without noticing anything at all, whilst others experience mild to moderate discomfort. Testing is the only way to determine whether Mgen is present.

Understanding Mycoplasma Genitalium

Mycoplasma Genitalium is a small bacterial organism that can be transmitted through sexual contact. It is considered a sexually transmitted infection (STI) and has been increasingly recognised as a significant cause of urogenital symptoms in both men and women.

In men, Mgen is associated with urethritis — inflammation of the urethra — which may present as discharge or discomfort. In women, it has been linked to cervicitis, pelvic inflammatory disease (PID), and in some cases fertility concerns if left untreated over time.

Despite its clinical significance, Mgen is not included in standard NHS sexual health screens as routinely as infections such as chlamydia, meaning many cases go undetected without specific testing.

Why Macrolide Resistance Matters

Macrolide antibiotics — most commonly azithromycin — have historically been the first-line treatment for Mycoplasma Genitalium. However, over recent years, antibiotic resistance has become a serious concern within sexual health medicine.

Studies across Europe and the UK have reported macrolide resistance rates in Mgen of between 40% and 60% in some populations. This means that in a significant proportion of cases, standard antibiotic treatment may not successfully clear the infection.

When resistance is present but undetected, a patient may complete a full course of antibiotics, experience initial symptom improvement, and then find that the infection has not resolved — or has returned. This not only prolongs discomfort but can inadvertently contribute to further resistance development.

A macrolide resistance test analyses the genetic material of the Mgen bacteria detected in a sample to identify specific mutations — most commonly in the 23S rRNA gene — that confer resistance. This information allows clinicians or GPs to choose an alternative antibiotic regimen from the outset, making treatment more targeted and potentially more effective.

Why the Macrolide Resistance Test is Bundled with Mgen Screening

The reason these two tests are routinely offered together — rather than separately — is straightforward: the resistance result is only meaningful if Mgen is actually detected. Running the resistance test in isolation would provide no clinical information.

Conversely, detecting Mgen without knowing whether it is macrolide-resistant could lead to inappropriate treatment. Current UK sexual health guidelines from the British Association for Sexual Health and HIV (BASHH) recommend that macrolide resistance testing is performed at the same time as Mgen detection, as this shapes the most appropriate management pathway.

Bundling the two tests also simplifies the process for patients. A single sample — typically a urine sample or genital swab — can provide both results simultaneously through modern PCR (polymerase chain reaction) laboratory analysis.

Common Symptoms Associated with Mgen

Symptoms that may, in some cases, be associated with Mycoplasma Genitalium include:

• Unusual discharge from the urethra or vagina
• Burning or stinging sensation during urination
• Pelvic discomfort or pain during sex
• Vaginal bleeding between periods or after intercourse
• Mild urethral irritation in men

It is important to note that many individuals with Mgen experience no symptoms whatsoever. Symptoms such as these can also arise from other causes entirely, including other STIs such as chlamydia or gonorrhoea, non-infectious irritation, or hormonal changes. Symptoms alone cannot differentiate between these possibilities.

How STI Symptoms Can Overlap With Other Conditions

The symptoms most commonly associated with Mgen closely resemble those of several other conditions. Chlamydia, gonorrhoea, trichomoniasis, and non-specific urethritis can all present with similar patterns of discharge or discomfort. Even non-infectious causes — such as contact irritation from hygiene products, hormonal fluctuations, or minor skin sensitivity — can produce comparable symptoms.

This overlap is precisely why laboratory testing is necessary. Visual assessment of symptoms, whether by a patient or even a clinician without testing, cannot reliably identify the specific cause.

When STI Testing May Be Worth Considering

Testing for Mycoplasma Genitalium with a macrolide resistance test may be a sensible consideration in situations such as:

• Symptoms such as discharge, urethral irritation, or pelvic discomfort that are persistent or unexplained
• Recent unprotected sexual contact with a new partner
• A sexual partner who has been diagnosed with Mgen or another STI
• Symptoms that have not responded to previous treatment
• Routine screening as part of a broader sexual health check

Suitability for testing and appropriate next steps depend on individual clinical circumstances. Please discuss your specific situation with a clinician or healthcare professional.

A full STI screen is often the most thorough approach, as Mgen can coexist alongside other infections.

How Mgen Testing Works

Testing for Mycoplasma Genitalium is a straightforward process. The sample required is typically:

• A first-catch urine sample (the initial portion of a urine stream)
• A genital swab (urethral, vaginal, or cervical depending on anatomy and clinical context)

The sample is analysed in a laboratory using PCR technology, which detects the genetic material of the Mgen organism. If Mgen is detected, the same sample is then analysed for the genetic mutations associated with macrolide resistance. Results are typically available within a few working days, though turnaround times may vary. All results are communicated confidentially.

When Symptoms Are Less Likely to Be Related to an STI

Not every episode of genital discomfort or unusual discharge points to an infection. Temporary irritation can result from:

• Friction during sexual activity
• Sensitivity to soaps, shower gels, or fabric conditioners
• Post-shaving irritation
• Hormonal changes affecting discharge consistency
• Minor skin conditions unrelated to infection

If symptoms are mild, short-lived, and resolve without intervention, they may well have an entirely non-infectious explanation. However, if symptoms persist or are associated with potential exposure, testing may help provide clarity.

Frequently Asked Questions

Can I have Mycoplasma Genitalium without any symptoms?

Yes. Mgen is frequently asymptomatic, meaning many people carry the infection without being aware of it. This is one reason why targeted testing following potential exposure is advisable even in the absence of symptoms.

Does a positive Mgen result always mean I need a specific antibiotic?

Not necessarily the same one. The macrolide resistance result helps determine which antibiotic is most likely to be effective. This information should be shared with your GP or treating clinician, who will advise on the most appropriate management.

Should I still test if my symptoms have disappeared?

Symptoms resolving does not confirm that an infection has cleared. Mgen can persist without causing noticeable symptoms. If there has been a potential exposure, testing is still worth considering even if initial symptoms have subsided.

How soon after potential exposure should I test for Mgen?

A window period of approximately two to five weeks after potential exposure is generally recommended before testing, to allow the organism to reach detectable levels. Your clinic can advise based on your specific circumstances.

Is a macrolide resistance test the same as a standard antibiotic sensitivity test?

Not exactly. The macrolide resistance test for Mgen uses PCR to look for specific genetic mutations linked to resistance, rather than traditional culture-based sensitivity testing. It is specifically designed for this organism and provides actionable information quickly.

Can Mgen be detected as part of a broader STI screen?

Mgen is not always included in standard STI panels. It is important to check that the screen you choose specifically includes Mycoplasma Genitalium with macrolide resistance testing if this is a concern for you. A full STI screen may cover a wider range of infections including chlamydia, gonorrhoea, and others.

When to Seek Medical Advice

You may wish to seek appropriate medical advice if you experience:

• Severe or worsening pelvic pain
• Significant unusual discharge accompanied by fever
• Sores, ulcers, or lesions in the genital area
• Symptoms that persist or worsen over time
• Recurrence of symptoms following treatment

If symptoms persist or worsen, consultation with an appropriate healthcare service — such as your GP or an NHS sexual health clinic — may be advised.

Confidential STI Testing in the UK

If you are concerned about possible Mgen symptoms or potential exposure, confidential STI testing appointments are available at our UK clinic. Testing decisions depend on symptoms, exposure history, and individual risk factors. We can advise on which tests may be appropriate for your circumstances, and our team handles all enquiries with complete discretion.

Visit our main STI testing page or our full STI screen page to find out more about the options available.

Medical Disclaimer: This article is for general informational purposes only and does not constitute medical advice, diagnosis, or treatment. Sexual health concerns should be assessed based on individual circumstances. If you are experiencing persistent, severe, or worsening symptoms, consultation with an appropriate healthcare service is advised. Our clinic provides private STI testing services only.