Abstract
To evaluate the revision to the 2025 Clinical and Laboratory Standard Institute (CLSI) breakpoints revision on the interpretation of minocycline for Acinetobacter baumannii complex, by comparing the minimum inhibitory concentrations obtained by broth microdilution (BMD) with inhibition zone diameters measured by disk diffusion testing. A total of 276 non-duplicate clinical isolates of A. baumannii complex were collected in China between 2022 and 2024, including 150 carbapenem-resistant A. baumannii (CRAB) isolates and 126 carbapenem-susceptible A. baumannii isolates. Antimicrobial susceptibility testing was performed using BMD and disk diffusion, with results interpreted per the 2024 and 2025 breakpoints, respectively. Categorical agreement and error rates were calculated to assess performance. Compared to the 2024 CLSI breakpoints, the updated 2025 CLSI breakpoints reduced the susceptibility rate of A. baumannii complex to minocycline (from 73.9% to 46.4%) and increased the resistance rate (from 4.4% to 46.0%). For CRAB, the susceptibility rate dropped from 53.3% to 6.0%, while the resistance rate rose from 7.4% to 82.7%. Categorical agreement improved from 64.1% to 90.9%. The intermediate results proportion determined by disk diffusion decreased significantly (from 25.4% to 5.8%). Notably, 62.5% of isolates categorized as intermediate by disk diffusion were reclassified as either susceptible or resistant when tested by BMD. The revised 2025 CLSI breakpoints are clinically applicable. They reduce the susceptibility rate and increase the resistance rate of A. baumannii complex to minocycline. There is also improved categorical agreement and reduced error rates between disk diffusion and BMD. For isolates categorized as intermediate by disk diffusion, confirmation with BMD is recommended. IMPORTANCE: The Clinical and Laboratory Standards Institute (CLSI) has made a comprehensive revision of minocycline breakpoints for Acinetobacter species in 2025. This update may have a significant impact on antimicrobial susceptibility testing interpretation and treatment strategies for clinical laboratories. However, there is currently a lack of comparative studies about it. Therefore, this study aims to evaluate the impact of the 2025 CLSI breakpoints revision on the interpretation of minocycline for Acinetobacter baumannii complex and to provide experimental evidence for the clinical applicability of new breakpoints.