Defining Fluoroquinolone Resistance-Mediating Mutations from Non-Resistance Polymorphisms in Mycoplasma hominis Topoisomerases.

Martin Sharratt,Kirsty Sands,Brian A Mondeja,Ian Boostrom,Owen B Spiller,Lucy C Jones,Edward A R Portal,Nadia M Rodríguez

doi:10.3390/antibiotics10111379

Abstract

Often dismissed as a commensal, Mycoplasma hominis is an increasingly prominent target of research due to its role in septic arthritis and organ transplant failure in immunosuppressed patients, particularly lung transplantation. As a mollicute, its highly reductive genome and structure render it refractile to most forms of treatment and growing levels of resistance to the few sources of treatment left, such as fluoroquinolones. We examined antimicrobial susceptibility (AST) to fluoroquinolones on 72 isolates and observed resistance in three (4.1%), with corresponding mutations in the quinolone resistance-determining region (QRDR) of S83L or E87G in gyrA and S81I or E85V in parC. However, there were high levels of polymorphism identified between all isolates outside of the QRDR, indicating caution for a genomics-led approach for resistance screening, particularly as we observed a further two quinolone-susceptible isolates solely containing gyrA mutation S83L. However, both isolates spontaneously developed a second spontaneous E85K parC mutation and resistance following prolonged incubation in 4 mg/L levofloxacin for an extra 24–48 h. Continued AST surveillance and investigation is required to understand how gyrA QRDR mutations predispose M. hominis to rapid spontaneous mutation and fluoroquinolone resistance, absent from other susceptible isolates. The unusually high prevalence of polymorphisms in M. hominis also warrants increased genomics’ surveillance.

Highlights

IntroductionMycoplasma hominis is an uncommon urogenital colonizer that belongs to the Mollicutes class of bacteria
We further showed evidence of fluoroquinolone-susceptible strains carrying quinolone resistance-determining region (QRDR) mutations in the gyrA gene that were able to spontaneously gain a parC mutation after prolonged incubation with higher concentrations of levofloxacin, which was not observed in isolates without gyrA mutations
We investigated the prevalence of non-resistance polymorphisms in these key genes for M. hominis, which could obfuscate a genomics-based approach to resistance screening for this bacterium

Summary

Introduction

Mycoplasma hominis is an uncommon urogenital colonizer that belongs to the Mollicutes class of bacteria. Mollicutes are one of the simplest forms of self-replicating life, and as such are resistant to most of the treatment methods normally employed by clinicians. They lack the cell walls that are targeted by beta-lactams and glycopeptides and lack the folic acid pathways that would be inhibited by sulphonamides and trimethoprim [6]. M. hominis itself is naturally resistant to 14- and 15-membered ring macrolides [7] and incredibly fastidious, making in vitro growth and/or detection incredibly laborious. The remaining therapeutics for treatment are macrolides, tetracyclines, and fluoroquinolones, the last of which is the family to which ciprofloxacin, levofloxacin, and moxifloxacin belong

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Results

Conclusion