Comparison of ComASP® and UMIC® methods with the reference method for cefiderocol susceptibility testing on carbapenem-resistant Enterobacterales

Abstract

Therapeutic options for the treatment of infections caused by carbapenem-resistant Enterobacterales are often limited, especially for class B carbapenemases.Cefiderocol, a new siderophore cephalosporin, could be used as a last resort to treat infections caused by highly resistant Gram-negative strains including Enterobacterales, Pseudomonas aeruginosa and Acinetobacter baumannii.Cefiderocol remains active on strains producing Ambler class A, B, C and D -lactamases. 1 Overall, MICs of cefiderocol for Enterobacterales producing type A (KPC) or D (OXA-48-like) carbapenemases are low. 2,3However, many MBL-producing Enterobacterales, especially NDM-type producers, possess higher MICs resulting in higher resistant rates to cefiderocol. 2,3he reference method for the determination of cefiderocol susceptibility is MIC determination using the broth microdilution method (BMD) performed with an iron-depleted CAMHB (ID-CAMHB).Unfortunately, this broth is cumbersome to prepare in a clinical microbiology laboratory.Regarding commercially available tests, several studies revealed that MIC gradient strips were not accurate to determine cefiderocol susceptibility of P. aeruginosa and Enterobacterales. 2,4A recent study demonstrated that the disc diffusion method could be used for Enterobacterales but with a large area of technical uncertainty (ATU) (18-24 mm). 2 This study also proposed the Sensititre EUMDROXF microplates (Thermo Fisher) as a good alternative to the reference BMD method.However, it is crucial to evaluate other methods given that, since February 2022, EUMDROXF microplates can no longer be used to determine cefiderocol susceptibility due

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