Comparison of five commonly used automated susceptibility testing methods for accuracy in the China Antimicrobial Resistance Surveillance System (CARSS) hospitals Menglan Zhou,1–3 Yao Wang,1,3 Chang Liu,1–3 Timothy Kudinha,4 Xiaolin Liu,5,6 Yanping Luo,7 Qiwen Yang,1,3,6 Hongli Sun,1,3,6 Jihong Hu,8 Ying-Chun Xu1,3,6 1Department of Clinical Laboratory, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China; 2Graduate School, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China; 3Beijing Key Laboratory for Mechanisms Research and Precision Diagnosis of Invasive Fungal Diseases, Beijing, China; 4Department of Clinical Laboratory, Charles Sturt University, Leeds Parade, Orange, New South Wales, Australia; 5National Health and Family Planning Commission Expert Committee for Clinical Use of Antibiotics and Assessment of Bacterial Resistance, Beijing, China; 6Quality Management Center of China Antimicrobial Resistance Surveillance System (CARSS), Beijing, China; 7Department of Clinical Laboratory, Chinese PLA General Hospital, Beijing, China; 8National Center for Clinical Laboratories, Beijing Hospital, National Center of Gerontology, Beijing, China Objective: The objective of this study was to evaluate the performance of five commonly used automated antimicrobial susceptibility testing (AST) systems in China (Vitek 2, Phoenix, Microscan, TDR, and DL). Materials and methods: Two “unknown” isolates, S1 (ESBL-producing Escherichia coli) and S2 (KPC-producing Klebsiella pneumoniae), were sent to 886 hospitals in China for identification and AST. Using broth microdilution method (BMD) as gold standard, minimum inhibitory concentrations (MICs) were determined. Results: Most hospitals (392, 46.1%) used Vitek 2, followed by 16% each for Phoenix, Microscan, and DL systems, and 5.9% (50) used TDR system. MICs of 22 antimicrobials were evaluated for two study isolates plus three ATCC strains. Individual susceptibility results for three ATCC strains (n