The in vitro activity of the investigational siderophore cephalosporin, cefiderocol (formerly S-649266), was determined against a 2014-2016, 52-country, worldwide collection of clinical isolates of carbapenem-nonsusceptible Enterobacteriaceae (n = 1,022), multidrug-resistant (MDR) Acinetobacter baumannii (n = 368), MDR Pseudomonas aeruginosa (n = 262), Stenotrophomonas maltophilia (n = 217), and Burkholderia cepacia (n = 4) using the Clinical and Laboratory Standards Institute (CLSI) standard broth microdilution method. Iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB), prepared according to a recently approved (2017), but not yet published, CLSI protocol, was used to test cefiderocol; all other antimicrobial agents were tested using CAMHB. The concentration of cefiderocol inhibiting 90% (MIC₉₀) of isolates of carbapenem-nonsusceptible Enterobacteriaceae was 4 μg/ml; cefiderocol MICs ranged from 0.004 to 32 μg/ml, and 97.0% (991/1,022) of isolates demonstrated cefiderocol MICs of ≤4 μg/ml. The MIC₉₀s for cefiderocol for MDR A. baumannii, MDR P. aeruginosa, and S. maltophilia were 8, 1, and 0.25 μg/ml, respectively, with 89.7% (330/368), 99.2% (260/262), and 100% (217/217) of isolates demonstrating cefiderocol MICs of ≤4 μg/ml. Cefiderocol MICs for B. cepacia ranged from 0.004 to 8 μg/ml. We conclude that cefiderocol demonstrated potent in vitro activity against a 2014-2016, worldwide collection of clinical isolates of carbapenem-nonsusceptible Enterobacteriaceae, MDR A. baumannii, MDR P. aeruginosa, S. maltophilia, and B. cepacia isolates as 96.2% of all (1,801/1,873) isolates tested had cefiderocol MICs of ≤4 μg/ml.

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