679. In vitro Activity of Cefiderocol (CFDC), a Novel Siderophore Cephalosporin, Against Difficult-to-Treat-Resistant (DTR) Gram-Negative Bacterial Pathogens From the Multi-National Sentinel Surveillance Study, SIDERO-WT (2014–2017)

BACKGROUND: DTR organisms are defined as nonsusceptible to all high-efficacy, low-toxicity antibiotics (penicillins, cephalosporins, carbapenems, and quinolones), leaving physicians with limited first-line treatment options. Analyses of electronic health records have shown that patients with DTR Gram-negative bacterial infections are more likely to receive inappropriate antibiotic therapy, have longer hospital stay and increased risk of mortality. CFDC is a novel parenteral siderophore cephalosporin with potent activity against aerobic Gram-negative pathogens, including carbapenem-resistant strains. We evaluated the in vitro activity of CFDC and comparators against DTR pathogens collected by the SIDERO-WT surveillance study. METHODS: A total of 30,459 clinical isolates of Gram-negative bacilli were systematically collected from United States, Canada, and 11 EU countries during 2014–2017. MICs were determined by broth microdilution for a panel of 7 antibiotics, including CFDC, ceftazidime–avibactam (CZA), ceftolozane–tazobactam (C/T), colistin (CST), cefepime (FEP), meropenem (MEM), and ciprofloxacin (CIP) according to CLSI guidelines. All antibiotics were tested in cation-adjusted Mueller–Hinton broth (CAMHB) except CFDC, for which iron-depleted CAMHB was used. Susceptibility was determined according to CLSI interpretive breakpoints except CST, where EUCAST breakpoints were used. DTR pathogens were defined as being nonsusceptible to FEP, MEM, and CIP according to CLSI breakpoints. RESULTS: Among 30,459 Gram-negative isolates collected between 2014 and 2017, 9.3% were nonsusceptible to FEP, MEM, and CIP and could be defined as DTR. DTR was most frequently observed in Acinetobacter spp. (55.5%), followed by Burkholderia spp. (19%), Pseudomonas aeruginosa (9.5%), and Enterobacterales (2.7%). Of the 1,173 Stenotrophomonas maltophilia tested, 97% had MEM MIC of ≥8 mg/L; however, only 2.9% could be defined as DTR. Cefiderocol was the most active antibiotic tested against DTR isolates with 94.5% DTR-Acinetobacter spp., 98.3% DTR-P. aeruginosa, and 99.8% DTR-Enterobacterales susceptible (Table 1). CONCLUSION: CFDC demonstrated potent activity against DTR Gram-negative pathogens with limited first-line treatment options. [Image: see text] DISCLOSURES: All authors: No reported disclosures.