Molecular diagnostics developer SpeeDx Pty Ltd, Sydney, Australia, has announced clinical data supporting the use of resistance-guided therapy for more-effective treatment of sexually transmitted infections (STIs) caused by Mycoplasma genitalium (MG). The study authors used the SpeeDx ResistancePlus MG test and recorded an overall cure rate greater than 92%, which represents a significant increase over the 67% cure rates previously achieved without resistance-guided therapy.1

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Colin Denver, SpeeDx.

The ResistancePlus MG test simultaneously detects M. genitalium and the genetic markers linked to antimicrobial resistance. The test is CE marked and in use in Europe and in laboratories across Australia and New Zealand. Clinical trials are under way in the United States in preparation for de novo clearance of the test by FDA. Currently, no FDA-cleared molecular diagnostic test for the detection of M. genitalium exists in the United States.

“This is a seminal publication demonstrating a remarkable improvement in treating what has essentially become an STI superbug,” says Colin Denver, CEO of SpeeDx. “Using diagnostics to define appropriate treatment decisions is key when dealing with the global health threat of antimicrobial resistance.”

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Catriona Bradshaw, MBBS, FACHSHM, PhD, University of Melbourne.

“I’ve seen resistance to azithromycin, the frontline recommended treatment for M. genitalium infection, rise to over 50% in Melbourne over the last decade,” says senior study author Catriona Bradshaw, MBBS, FACHSHM, PhD, a University of Melbourne associate professor who has worked on M. genitalium for 15 years. “Unfortunately, it’s now a situation mirrored in many countries around the world.”

Within the context of high-level resistance and ongoing use of azithromycin, which increases macrolide resistance, the team developed a three-tier treatment pathway. First, they switched from azithromycin to doxycycline for initial treatment, followed by testing with ResistancePlus MG to detect macrolide resistance biomarkers. Patients whose test results revealed macrolide resistance underwent treatment with a quinolone antibiotic (sitafloxacin) to avoid unnecessary and ineffective use of azithromycin. Patients whose test results revealed no macrolide resistance underwent treatment with a higher than standard dose of azithromycin over 4 days to reduce the development of de novo resistance.

Importantly, doxycycline use for initial STI treatment reduces overall use of azithromycin and reduces bacterial load, which the authors hypothesize improves the effectiveness of subsequent macrolide or quinolone treatment. Ongoing work will evaluate the use of moxifloxacin rather than sitafloxacin following doxycycline, as this agent is more widely available.

Data from the study have already influenced recent STI management guideline updates in Australia and the United Kingdom, which now recommend using doxycycline upfront and assessing the resistance status of M. genitalium infections to guide treatment. Applying diagnostics to define appropriate treatment decisions is also in line with recent recommendations on global management of antimicrobial resistance. Resistance-guided therapy results in more-effective use of antibiotics, curtails inappropriate prescribing, and preserves key medicines necessary to combat the global rise of antimicrobial resistance.

To learn more, visit SpeeDx.


  1. Read TRH, Fairley CK, Murray GL, et al. Outcomes of resistance-guided sequential treatment of Mycoplasma genitalium infections: a prospective evaluation. Clin Infect Dis. 2018; Epub ahead of print, June 5; doi: 1093/cid/ciy477.