Mycoplasma genitalium: Using a commercial molecular technique that facilitates rapid detection of mutations associated with resistance to macrolides

The bacterium Mycoplasma genitalium (MG) is a species recently described as a cause of sexually transmitted infections, with particular importance due to its resistance to some antibiotics.¹ The accepted empirical treatment in episodes of non-gonococcal urethritis is doxycycline (IUSTI and ECDC guidelines) and azithromycin (CDC guidelines). The indicated dosage of azithromycin is 500 mg/first day and 250 mg/four further days. The reports in the literature of variable and increasing rates of MG macrolide resistance make it necessary to analyse its susceptibility to these antibiotics. The IUSTI European guidelines recommend the use of molecular tests for the detection of MG and associated resistance, as they provide a clinical advantage and propose the most appropriate treatment. As little is known in Spain about the susceptibility of MG to macrolides,^2,3 we decided to carry out a study of the mutations associated with macrolide resistance on strains isolated at our hospital.

We studied 20 clinical samples frozen at 80 °C from 17 patients, corresponding to 17 episodes of infection. In these samples, MG had been previously detected by commercial PCR (BD Max Mycoplasma/Ureaplasma®, Madrid, Spain). There were 15 samples from 12 males (eight urethral exudate, four rectal exudate, two balanopreputial exudate and one semen sample) and five samples from five females (four endocervical exudate and one vaginal exudate). These patients were studied in the Urology, Gynaecology, Infectious Diseases and Accident and Emergency Department of Hospital Virgen de las Nieves in Granada, from April 2017 to September 2018. The mean age of the patients was 26.2 years (18–36 years). All samples were analysed simultaneously using the ResistancePlus® MG kit (SpeeDx), a multiplex qPCR which, in a single well, detects MG and five mutations in 23S rRNA associated with azithromycin resistance (A2058G, A2059G, A2058T, A2058C and A2059C).

Of the 20 samples studied, three were negative for the detection of MG. In the identification by BD MAX, these samples had shown some amplification cycle (Ct) values greater than 30. Of the 17 positive samples, corresponding to 15 infection episodes, mutations were found in six samples corresponding to four episodes (26.7%). These six samples belonged to four patients (three males and one female). After reviewing their medical records as far as it was documented, it seemed that given the absence of any subsequent specific treatment, the positive result for MG had not been assessed by the treating physician.

This study needs to be extended with more positive MG samples to assess the level of resistance in the different study populations. The ResistancePlus® MG test was simple to perform and adapted to the routine practice of our laboratory. The PlexPCR® technique failed to detect MG in three samples. However, considering its relatively high Ct values, we assume a low positivity which, added to the freeze/thaw process, may explain the negative result. The results of the test used are in accordance with the latest recommendations for the management of patients infected with MG with the aim of optimising antibiotic therapy and potentially reducing the transmission of azithromycin resistance. In conclusion, it is important to recommend the early analysis of macrolide susceptibility in MG, in this case facilitated by the use of a commercial technique.

Funding

The authors declare that they have not received any specific funding for this study.