Evaluating Antimicrobial Susceptibility Testing Methods for Cefiderocol: A Review and Expert Opinion on Current...

Area of Science:

• Clinical Microbiology
• Antimicrobial Resistance
• Infectious Diseases

Background:

• Cefiderocol (FDC) antimicrobial susceptibility testing (AST) presents significant challenges.
• The reference broth microdilution (BMD) method using iron-depleted cation-adjusted Mueller-Hinton broth (ID-CAMHB) is cumbersome for routine use.
• Commercial AST systems show variable accuracy, compounded by unclear interpretive criteria and technical uncertainties.

Purpose of the Study:

• To review current FDC AST methods for key bacterial pathogens.
• To provide a practical decision framework for clinical microbiologists.
• To address the complexities of cefiderocol susceptibility testing.

Main Methods:

• Review of existing literature on cefiderocol AST.
• Expert opinion on performance of current FDC AST methods.
• Development of a decision framework for AST interpretation.

Main Results:

• Disk diffusion (DD) is proposed as a preliminary screening tool for Enterobacterales and Pseudomonas aeruginosa.
• Confirmatory testing with UMIC® FDC system or ID-CAMHB BMD is recommended for resistant isolates.
• A stepwise framework is proposed for Acinetobacter baumannii complex based on DD results and zone sizes.

Conclusions:

• Disk diffusion can guide initial cefiderocol susceptibility classification for Enterobacterales and P. aeruginosa.
• Confirmatory testing is crucial for non-susceptible isolates and those in areas of technical uncertainty.
• A tailored approach is needed for Acinetobacter baumannii complex due to lack of defined breakpoints.