Int J STD AIDS. 2013 Oct;24(10):822-8.

Failure of moxifloxacin treatment in Mycoplasma genitalium infections due to macrolide and fluoroquinolone resistance.

Couldwell DL, Tagg KA, Jeoffreys NJ, Gilbert GL.

Western Sydney Sexual Health Centre, Westmead Hospital, Parramatta, NSW, Australia.



Background. Increasing azithromycin (AZM) treatment failure, in sexually transmitted Mycoplasma genitalium infections, is linked to macrolide resistance and second-line treatment relies on the fluoroquinolone, moxifloxacin (MXF). We recently detected fluoroquinolone and macrolide resistance-associated mutations in 15% and 43%, respectively, of 143 initial M. genitalium PCR-positive specimens.

Methods/Results.  For a subset of 33 Western Sydney Sexual Health Centre patients, clinical information and results of sequence analysis of M. genitalium macrolide and fluoroquinolone target genes – the 23S rRNA gene, and parC and gyrA, respectively – were used to examine whether mutations were associated with treatment failure. Macrolide resistance-associated mutations correlated with microbiological (p=0.013) and clinical (p=0.024) treatment failure, and fluoroquinolone resistance-associated mutations with microbiological MXF treatment failure (p=0.005). We describe the first reported cases of clinical and microbiological MXF treatment failure.

Conclusions.  Failure of first- and second-line antibiotic treatment of M. genitalium infection is occurring and likely to increase with current treatment strategies.

KEYWORDS: Australia, Mycoplasma genitalium, STI, Sexually transmitted infections, antibiotic, bacterial disease, location, non-gonococcal urethritis, resistance, treatment, treatment failure

PMID: 24052013


The sexually transmissible infection (STI) Mycoplasma genitalium causes up to 25% of cases of nongonococcal urethritis (NGU), a common STI-related syndrome among men. M. genitalium is the second most frequent cause of NGU after Chlamydia trachomatis, and both organisms are also associated with cervicitis and pelvic inflammatory disease in women. While chlamydia is known to be an important cause of reproductive morbidity, the  health outcomes of M. genitalium infection are not fully understood, a commercial test for infection is not yet available, and antibiotic resistance is emerging as a major treatment hurdle. Clinicians are struggling to incorporate testing and treatment of M. genitalium infection into STI guidelines. A single dose of azithromycin 1 g (AZM) is a common first-line treatment for NGU, and the fluoroquinolone antibiotic, moxifloxacin (MXF), is used when AZM fails to cure M. genitalium infection.Increasing AZM treatment-failure1  is linked to macrolide-associated resistance mutations in the 23S rRNA gene of M. genitalium,  which may be transmitted sexually with resistant strains, or emerge following exposure to AZM.2 Mutations in the fluoroquinolone target genes parC and gyrA are associated with resistance to fluoroquinolone antibiotics among other mycoplasmas and ureaplasmas.3 However, there had been no clinical reports of MXF treatment failure associated with these mutations in M. genitalium infection when we planned our research.

The first step was to characterise potential antibiotic resistance among local strains of M. genitalium. In the study period, our laboratory performed all testing for M. genitalium in Sydney, and had stored M. genitalium-positive samples, so we postulated that the prevalence of antibiotic resistance-associated mutations in the initial patient samples would reflect community prevalence. From sample DNA extracts, the target genes, 23S rRNA, parC and gyrA, were amplified and sequenced, then aligned against the corresponding M. genitalium G37 sequences and analysed using bioinformatics software. The paper describing these laboratory methods in detail was published in 2013.4 To ascertain whether the detected mutations were indeed associated with treatment failure, we then examined medical records of patients from one sexual health clinic, and correlated the laboratory and clinical findings. The conclusions of our laboratory study were somewhat modified, as we found that some patients had already been treated with AZM prior to initial testing for M. genitalium. Therefore, macrolide resistance among local M. genitalium strains was overestimated when clinical data was not taken into account. Nevertheless, AZM treatment failure was not uncommon , occurring in 20% of men with no history of previous treatment.  M. genitalium strains from patients who failed AZM treatment were very likely to harbour macrolide resistance mutations, and these mutations could either be acquired with the infection (sexually transmitted), or emerge following AZM treatment, confirming previous research findings. However, none of the patients had been treated with MXF prior to testing, so prevalence of mutations in initial samples did reflect population prevalence of fluoroquinolone resistance. We described cases of patients who failed both first- and second-line treatment, and had fluoroquinolone resistance-associated mutations in DNA extracts of their specimens before and after MXF treatment. Alarmingly, 15% of M. genitalium strains circulating in our community were resistant to the second-line antibiotic5 MXF, and no alternative antibiotic treatment has been evaluated to date.

Researchers world-wide are reporting increasing antibiotic resistance in M. genitalium infections, driven by a sub-optimal first-line treatment for NGU, sexually transmitted and emergent macrolide resistance, and circulating fluoroquinolone resistance mutations. The lack of systematic testing for M. genitalium is also contributing to our failure to manage this infection.  New testing methods and more effective therapies are urgently needed to control M. genitalium infection.


List of Figures

Picture1 Transmission electron micrographFigure 1. Transmission electron micrograph of M. genitalium negatively stained with ammonium molybdite. Taylor-Robinson D, and Jensen JS. Clin Microbiol Rev 2011;24:498-514. Reprinted with permission.

Mutations[2]Figure 2. 23S rRNA sequencing chromatograph. The top sequence shows a wild type strain showing no 23S rRNA mutations. The bottom sequence shows an A–>G mutation at position 2059, associated with resistance to macrolide antibiotics.



Figure 3. Kaitlin Tagg in the laboratory at the Centre for Infectious Diseases and Microbiology, Institute of Clinical Pathology and Medical Research, Westmead Hospital



  1. Manhart LE, Gillespie CW, Lowens MS, et al. Standard treatment regimens for nongonococcal urethritis have similar but declining cure rates: a randomized controlled trial. Clin Infect Dis 2013; 56: 934-942.
  2. Twin J, Jensen JS, Bradshaw CS, et al. Transmission and selection of macrolide resistant Mycoplasma genitalium infections      detected by rapid high resolution melt analysis. PLoS One 2012; 7(4): e35593.
  3. Shimada Y, Deguchi T, Nakane K, et al. Emergence of clinical strains of Mycoplasma genitalium harbouring alterations in ParC      associated with fluoroquinolone resistance. Int J Antimicrob Agents 2010; 36: 255-258.
  4. Tagg KA, Jeoffreys NJ, Couldwell DL, Donald JA, Gilbert GL. Fluoroquinolone and macrolide resistance-associated mutations in Mycoplasma genitalium. J Clin Microbiol  2013; 51: 2245-9.
  5. Couldwell DL, Tagg KA, Jeoffreys NJ, Gilbert GL. Failure of moxifloxacin treatment in Mycoplasma genitalium infections due to macrolide and fluoroquinolone resistance. Int J STD AIDS 2013; 24(10); 822-828.
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