Susceptibility to cefiderocol and other novel antibiotics against carbapenem-non-susceptible gram-negative bacilli

Cefiderocol (CFDC) is a novel siderophore cephalosporin with a unique cell entry feature and a high stability against a wide range of β-lactamases. We conducted antimicrobial susceptibility testing on 89 clinical isolates of carbapenem-non-susceptible gram-negative bacilli (CNS-GNB) strains detected at our hospital, evaluating the efficacy of novel antibiotics including CFDC, ceftolozane/tazobactam, ceftazidime/avibactam, and imipenem/cilastatin/relebactam. The strains included were as follows, 21 carbapenemase-producing Enterobacterales (CPE), 40 carbapenem-resistant Pseudomonas aeruginosa (CRPA), and 28 Stenotrophomonas maltophilia. Carbapenemase production were detected using NG-Test^® CARBA 5. Carbapenemase genes were analyzed by PCR-sequencing and extended-spectrum β-lactamase (ESBL) genes were detected by PCR. CPE isolates produced 17 IMP-, 3 NDM-, and one KPC-type carbapenemases, and 12 out of 21 CPE isolates produced ESBLs. All 40 CRPA did not produce carbapenemases. All 21 CPE isolates and 95% of CRPA were susceptible to CFDC. Colistin were intermediate against all CPE and 92.5% of CRPA isolates. In S. maltophilia isolates, susceptibility to CFDC and trimethoprim-sulfamethoxazole were 100% and 89.3 %. Although non-susceptibility to CFDC appeared in 2 CRPA isolates, MIC₉₀ of CFDC was within susceptible range against all three groups of clinical isolates. CFDC showed significant promise as a treatment option for infections caused by CNS-GNB.