Introduction: Acinetobacter baumannii is an aerobic Gram-negative bacterium which causes facultative hospital infections and in settings like Greece exhibits high resistance rates against most antimicrobial agents. Cefiderocol is a siderophore cephalosporin intended to treat infections due to multi-drug resistant (MDR) Gram negative aerobic bacteria. The aim of our study was to assess the in vitro activity of cefiderocol and comparators against multidrug resistant Acinetobacter baumannii isolates.

Methods: A total of 29 MDR Acinetobacter baumannii strains recovered from clinical samples (23 blood, 2 central line catheters, 2 bronchial aspirates, 1 pus and 1 urine) from January to April 2022 were included in the study. Species identification and antimicrobial susceptibility testing for most comparators were performed with the Vitek®2 automated system (bioMérieux, France) except for colistin tested by the broth microdilution method using the ComASP™ Colistin 0.25-16 μg/mL panel (Liofilchem®) and tigecyclin tested by Liofilchem® MIC Test Strips. Cefiderocol MICs were determined via the Liofilchem® MIC Test Strips on Mueller Hinton II Agar (BD™). MIC₅₀ and MIC₉₀ were calculated for all antimicrobials and EUCAST 2022 clinical breakpoints were applied wherever applicable. Susceptibility to tigecyclin was interpreted according to the FDA breakpoints and to cefiderocol according to the EUCAST PK/PD breakpoints. Pseudomonas aeruginosa ATCC25853 and Klebsiella pneumoniae ATCC700603 were used as quality control.

Results: Cefiderocol MICs ranged from 0.064 to >256 mg/L with the majority of the isolates being susceptible. The comparators had very low to zero susceptibility rates against the tested isolates. MIC₅₀, MIC₉₀, MIC range and susceptibility rates are displayed analytically on Table 1.

Discussion: Cefiderocol exhibited potent in vitro activity against MDR Acinetobacter baumannii isolates. It seems to be a valuable option where limited or no therapeutic alternatives are available.