Antimicrobial Susceptibility and Distribution Characteristics of Mycoplasma pneumoniae Isolates in Beijing, China, from 2017 to 2025

<b>Background/Objectives</b>: The aim of this study was to clarify the antimicrobial susceptibility and distribution characteristics of <i>Mycoplasma pneumoniae</i> (<i>M. pneumoniae</i>, MP) collected from children in Beijing, China, from 2017 to 2025. <b>Methods</b>: A total of 197 MP isolates were analyzed. Mutations in macrolide-resistant loci of MP strains were detected via real-time fluorescent quantitative polymerase chain reactions. We used the broth microdilution method to determine the minimum inhibitory concentrations (MICs) of erythromycin, azithromycin, tetracycline, levofloxacin, and moxifloxacin against these isolates. The distribution characteristics of MIC values were further analyzed according to the isolates' collection year, epidemic phase (low epidemic phase, epidemic initiation phase, ultra-low epidemic phase, outbreak phase, and epidemic recovery phase), and the corresponding patient age group (<3 years, 3-6 years, and ≥6 years). <b>Results:</b> All 197 isolates were found to be resistant to erythromycin and azithromycin, with a resistance rate of 100%. In contrast, the strains remained susceptible to tetracycline, levofloxacin and moxifloxacin. The highest resistance rate was 100% for macrolides. The MIC₉₀ values were 1024 μg/mL for erythromycin, 256 μg/mL for azithromycin, 0.5 μg/mL for tetracycline, 1 μg/mL for levofloxacin, and 0.125 μg/mL for moxifloxacin, respectively. Distinct differences in MIC distributions of erythromycin and azithromycin were observed across collection years, epidemic phases, and age groups. <b>Conclusions</b>: The resistance of MP to macrolides in children is closely associated with the epidemic intensity and age of the patient. Erythromycin is no longer suitable as an empirical therapy for MP infections during epidemic periods, whereas azithromycin can be cautiously administered in young children according to age stratification and MIC detection results. Meanwhile, it is imperative to strengthen the prevention and control of cluster MP infections during epidemic phases to reduce the transmission of drug-resistant MP strains.