Antibiotic resistance mutations in Mycoplasma genitalium and non-gonococcal urethritis treatment outcomes

BACKGROUND: In the Netherlands, Mycoplasma genitalium (MG) shows high macrolide resistance (75%) and increasing fluoroquinolone resistance (10%), limiting azithromycin and moxifloxacin efficacy. Despite high macrolide resistance, non-gonococcal urethritis (NGU) guidelines recommend delaying moxifloxacin until four weeks after azithromycin. This study evaluated microbiological and clinical cure of MG following sequential azithromycin and moxifloxacin treatment in relation to antibiotic resistance. METHODS: Men with NGU at the Centre for Sexual Health Amsterdam underwent physical examination and urine testing. MG-positive participants were followed up to 6 weeks. All received azithromycin 1 g at baseline; moxifloxacin was administered at week 4 for persistent MG-NGU. Macrolide (23S rRNA, rplD, rplV) and fluoroquinolone (parC, parE, gyrA, gyrB) resistance mutations and mgpB genotypes were assessed using nanopore sequencing. RESULTS: Among 30 MG-NGU cases, azithromycin achieved low microbiological cure, with 22 remaining positive at week 4. By week 6, 21 participants attended follow-up. Moxifloxacin was prescribed to 14 participants: 1 with persistent NGU and MG positivity, 5 with persistent NGU despite MG clearance, 3 with persistent MG without NGU, and 5 with resolution of both. Among the 7 untreated participants, 5 remained MG-positive with persistent NGU and 2 remained MG-positive without NGU. Symptoms generally improved despite persistent microbiological or clinical findings. ParC S83I mutations occurred in both successfully and unsuccessfully treated participants. ParE and gyrB mutations were less frequent and usually co-occurred with parC. Two persistent infections carried combined parC S83I, parE G492E, and gyrB R464K mutations. CONCLUSIONS: Sequential azithromycin and moxifloxacin achieved limited microbiological cure and NGU resolution. Symptom improvement despite persistent infection highlights discordance between microbiological and clinical outcomes. ParC S83I was common but did not consistently predict moxifloxacin failure. Persistent infections with combined parC, parE, and gyrB mutations suggest cumulative effects, requiring further studies.