Macrolide Resistance Against Mycoplasma genitalium Symptomatic Male Urethritis

Mycoplasma genitalium can be the only cause of symptomatic urethritis in men who took ineffective antibiotics.

Data published in Clinical Infectious Diseases found that Mycoplasma genitalium can be the only cause of symptomatic urethritis in men who took ineffective antibiotics. Further, in Nanjing, China, nearly 90% of Mg was resistant to macrolides and fluoroquinolones.

The study determined that the overall prevalence of M genitalium in 1816 men with symptomatic urethritis at a single clinic for care of sexually transmitted diseases (STDs) in Nanjing, China, was 19.7%. In addition, 54.1% of M genitalium infections occurred in the absence of other sexually transmitted infection (STI) agents. Of the 166 men with single infection, 63.9% were prescribed or self-administered antibiotics in the 30 days before enrollment compared with those with coinfections (P <.0001). The most commonly taken antibiotics were of the macrolide class (26.5%), followed by cephalosporins (24.7%).

In men who had taken macrolides before enrollment, higher rates of infection with macrolide-resistant M genitalium (96.7%) were found (P <.03). Overall, the percentage of 23S RNA genes containing mutations responsible for resistance was 88.9%. Of these, 89.5% of parC and 12.4% of gyrA genes had mutations responsible for fluoroquinolone resistance. Most cases of M genitalium had combined mutations in 23S rRNA and parC genes (87.7%), and 10.4% had mutations in all 3 genes.

The researchers noted that these results may have underestimated the proportion of M genitalium infections seen in the general male population, based on comparisons with previous results, which included men who were asymptomatic. The study investigators also found that macrolide resistance of M genitalium increased significantly across the 5 years of the study, but single infection was more common in those who took antibiotics before enrollment, leading them to speculate that single infections were the result of antimicrobials that treated other STI agents but are ineffective toward M genitalium.

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The results of this study showed that M genitalium is associated with sexually acquired urethritis when present as a single pathogen, and in cases in which prior antibiotic use may select for a single M genitalium infection. Further, unprecedented high prevalence of macrolide and quinolone resistance was observed. Researchers concluded that antibiotic-resistant M genitalium is a problem, and resistance testing, together with antimicrobial therapy, is a potential approach to control the progression of this resistance. However, new classes of antimicrobials and advanced versions of older classes have yet to be systematically tested in controlled efficacy trials.


Li Y, Su X, Le W, et al. Mycoplasma genitalium in symptomatic male urethritis: macrolide use is associated with increased resistance [published online April 11 2019]. Clin Infect Dis. doi:10.1093/cid/ciz294