Antimicrobial susceptibility changes of Escherichia coli and Klebsiella pneumoniae intra-abdominal infection isolate-derived pathogens from Chinese intra-abdominal infections from 2011 to 2015 Hui Zhang,1 Dawei Tong,1 Aaron Johnson,2 Ge Zhang,1 Zhipeng Xu,1 Yang Yang,1 Jingjia Zhang,1 Dongxue Li,1 Simeng Duan,1 Yao Wang,1 Qiwen Yang,1 Yingchun Xu11Department of Microbiology, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Science, Beijing 100730, People’s Republic of China; 2Department of Microbiology, International Health Management Associates, Schaumburg, IL 60173-3817, USABackground: To explore the susceptibility trends of antimicrobials and resistance increase to antibiotics of Enterobacteriaceae isolated from patients in China with intra-abdominal infections (IAI) from 2011 to 2015.Methods: MIC90 and MIC50 values of 12 commonly used antibiotics from Escherichia coli and Klebsiella pneumoniae isolated from IAI samples were determined.Results: A total of 8,477 Gram-negative bacterial pathogens were collected from 21 medical centers in China. The majority of IAI isolate-derived pathogens were E. coli (3,854, 45.5%) and K. pneumoniae (1,670, 19.7%) of which 1,990 (23.5%) were consecutively collected from community acquired (CA) and 6,186 (73.0%) from hospital acquired (HA) IAIs. The drugs with the highest efficacy against E. coli and K. pneumoniae isolates derived from IAI samples were imipenem, ertapenem, amikacin and piperacillin-tazobactam. MIC90 values for piperacillin-tazobactam were 64 μg/mL in 2015 with fluctuations from 16–64 μg/mL through the years for E. coli, but were stable at ≥64 μg/mL from 2011 to 2015 for K. pneumoniae isolates. Susceptibilities to ertapenem, imipenem and amikacin were high for E. coli isolates throughout the study, but K. pneumoniae isolated from abscesses, colon and peritoneal fluid collected from medical and surgical ICUs showed an increasing trend of carbapenem resistance in 2015.Conclusion: In 2015 there was a trend of enhanced carbapenem resistance, particularly for K. pneumoniae isolated from IAI samples obtained from patients in ICUs.Keywords: MIC, Enterobacteriaceae, intra-abdominal infection, carbapenems, cefepime, piperacillin-tazobactam