Background. We have an incomplete understanding of the mechanisms behind Mycoplasma genitalium fluoroquinolone treatment failure, and this has hampered the development of the next generation of tests for resistance-guided therapy. While the contribution of some mutations in parC (e.g. G248T/S83I) is well established, the role of mutations in the homologous gene, gyrA is not well understood. This study investigated the contribution of gyrA mutations to fluoroquinolone failure.
Methods. Samples from 411 males and females undergoing treatment for M. genitalium infection (Melbourne Sexual Health Centre, March 2019–February 2020) were analyzed by Sanger sequencing (gyrA and parC). The association between mutations and microbiologic treatment outcome was analyzed for 194 patients treated with moxifloxacin who attended for test of cure. A pooled analysis was also performed using additional published data collected at the same centre.
Results. The most common parC mutation was G248T/S83I (21.1% of samples), followed by D87N (2.3%). The most common gyrA mutation was G285A/M95I (7.1%), followed by D99Y (0.7%). Dual parC/gyrA mutations were found in 8.6% of cases. One third of infections harboring parC G248T/S83I mutation had a concurrent mutation in gyrA conferring M95I. Mutations in gyrA co-occurred with parC S83I variations, hence the independent contribution of gyrA mutations to fluoroquinolone failure could not be assessed. However, treatment failure was higher in patients with combined parC S83I/gyrA mutations, when compared to infections with single parC S83I mutation alone; this was observed from analysis of (i) 194 cases in this study (81.2% vs 45.8%, p=0.047), and (ii) pooled analysis of a larger population of 535 cases (80.6% vs 43.2%; p=0.0027), indicating a strong additive effect.
Conclusions. M. genitalium infections with dual parC S83I/ gyrA mutations were more likely to fail moxifloxacin compared with parC S83I mutation alone. These data indicate that gyrA should be considered as a target for future resistance assays. We propose a strategy for the next generation of resistance-guided therapy incorporating parC and gyrA testing.
