Background: 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