Purpose: To evaluate the susceptibility rates of carbapenem-resistant (CR)-Enterobacterales strains from Chinese intra-abdominal infections (IAI), respiratory tract infections (RTI) and urinary tract infections (UTI) between 2015 and 2017 to colistin.
Methods: In total, 7138 Enterobacterales including 1074 CR-Enterobacterales strains were isolated from IAI+UTI+RTI samples and collected in 21 hospitals across 7 regions of China. Antimicrobial susceptibilities were determined at a central laboratory using CLSI broth microdilution and interpretive standards.
Results: From 2015 to 2017, E. coli (51.4%) and K. pneumoniae  (30.0%) accounted for the majority of Enterobacterales isolated from IAIs, UTIs and RTIs. The percentage of CR strains within the species was highest for S. marcescens  (27.9%), followed by K. pneumoniae  (24.8%), P. mirabilis  (22.6), K. oxytoca  (19.5%), E. cloacae  (17.7%), C. freundii  (12.5%), K. aerogenes  (11.0%) and lowest for E. coli  (6.9%). Colistin susceptibilities were generally higher in CS than in CR isolates and were 83.5% for CR-E. coli , 88.6% for CR-K. pneumoniae , 79.2% for CR-E. cloacae  and 87.5% for CR-K . aerogenes . For IAI and UTI isolates in particular, CR-E. coli  and CR-K. pneumoniae  showed a trend of decreasing susceptibility, which was especially noted for CR-E. coli  in UTI isolates, and for both organisms in IAI isolates susceptibility dropped markedly in 2017.
Conclusion: Colistin was a last resort antibiotics for empirical CR-Enterobacterales treatments, since especially the percentage of CR-K. pneumoniae  was 30.0% of all IAI, UTI and RTI isolates, with an incidence of 24.8% CR strains, of which 88.6% were susceptible to colistin. Also other analyzed CR-Enterobacterales showed colistin susceptibilities of ≥ 80.0%. However, resistance rates of IAI derived CR-K. pneumoniae  and CR-E. coli , and CR-K. pneumoniae  UTI isolates to colistin increased between 2015 and 2017, which should further be closely monitored.
Keywords: Enterobacterales, carbapenem, colistin, intra-abdominal infection, respiratory tract infection, urinary tract infection