Mycoplasma genitalium is an emerging sexually transmitted infection (STI) with increasing antimicrobial resistance, particularly among men who have sex with men (MSM). This study aimed to evaluate the incidence, clinical characteristics, and antibiotic resistance patterns of M. genitalium among symptomatic MSM and transgender women (TGW) attending a specialized STI clinic in Barcelona, Spain.

A retrospective observational study was conducted between January and December 2024. Symptomatic MSM and TGW patients diagnosed with M. genitalium through nucleic acid amplification testing (NAAT) were included. Macrolide and fluoroquinolone resistance mutations were detected using real-time PCR assays. Patients were treated according to European guidelines, with resistance-guided therapy.

Among 71 patients with M. genitalium infection, 53.5 % presented with urethritis and 42.3 % with proctitis. Coinfection with other STIs was detected in 35 %, and 29.5 % had a history of recent STI. Alarmingly, 85.9 % of patients carried azithromycin resistance-associated mutations, while 42.3 % showed dual resistance to azithromycin and moxifloxacin. A test of cure (TOC) was performed in 26 patients (36.6 %), with 23.1 % (6/26) of them remaining positive, mainly due to dual resistance. The remaining 45 patients were lost to follow-up, but no relapses were recorded in six months

The high prevalence of macrolide-resistant M. genitalium among MSM underscores the need for alternative first-line therapeutic strategies, particularly in settings with limited access to resistance testing. Further research is required to optimize treatment regimens and evaluate the cost-effectiveness of routine macrolide susceptibility testing in high-risk populations.