High Macrolide Resistance in Pediatric Mycoplasma pneumoniae

Pediatric surveillance from Beijing spanning 2017–2025 showed consistently high in vitro macrolide resistance among Mycoplasma pneumoniae isolates recovered across the study period.

197 pediatric Mycoplasma pneumoniae isolates were analyzed; specimens were collected from pediatric outpatients and inpatients at the Capital Center for Children’s Health.

The authors reported minimum inhibitory concentrations from broth microdilution testing and used PCR-based assays to detect macrolide-resistance mutations in the 23S rRNA gene (notably A2063G and A2064G). They reported that all isolates were resistant in vitro to erythromycin and azithromycin, and that the A2063G mutation was detected in 100% of isolates.

Within this resistant isolate set, the authors reported wide macrolide MIC distributions summarized using ranges and central tendency metrics from broth microdilution MIC testing. For erythromycin, the MIC range was 4–1024 μg/mL, with MIC50 512 μg/mL and MIC90 1024 μg/mL. For azithromycin, the MIC range was 1–512 μg/mL, with MIC50 64 μg/mL and MIC90 256 μg/mL.

By contrast, the same in vitro testing showed low MIC90 values for tetracycline, levofloxacin, and moxifloxacin in this isolate collection, as reported by the authors. Reported MIC90 values were 0.5 μg/mL for tetracycline, 1 μg/mL for levofloxacin, and 0.125 μg/mL for moxifloxacin. The article describes this as a susceptibility profile distinct from the macrolides, while keeping the presentation confined to laboratory MIC findings rather than clinical response.

Stratified analyses described statistically significant differences in erythromycin and azithromycin MIC distributions by collection year and by epidemic phase, and the authors also reported variation by pediatric age group, with children aged 3–6 years showing the greatest proportion of isolates with higher macrolide MIC values. In their interpretation, the authors related these MIC patterns to the local context of empiric therapy during epidemic periods and described age-stratified considerations alongside azithromycin MIC results.

The authors noted limitations, including a single-center design, an absence of susceptible isolates in the sample, and lack of systematic clinical baseline data, framing the report as laboratory surveillance with constrained clinical correlation.

Key Takeaways:

• The authors reported uniformly high macrolide resistance in vitro across the pediatric isolate set, alongside universal detection of the A2063G macrolide-resistance mutation.
• Macrolide MICs were high-level overall, while tetracycline and tested fluoroquinolones showed low MIC90s in vitro in the same surveillance dataset.
• MIC distributions varied by collection year, epidemic phase, and age group.