Cefiderocol susceptibility in carbapenem-resistant Acinetobacter baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia isolates: concordance of disk diffusion with the reference method and comparative analysis of CLSI-EUCAST criteria

This study investigated the in vitro activity of cefiderocol against Acinetobacter baumannii, Pseudomonas aeruginosa, and Stenotrophomonas maltophilia isolates, comparing disk diffusion (DD) and broth microdilution (BMD) methods. 145 isolates were tested using BMD in iron-depleted cation-adjusted Mueller-Hinton broth and DD. Results were interpreted via CLSI and EUCAST criteria. MBL genes were detected by PCR. Cefiderocol showed potent activity against P. aeruginosa (MIC90:2 mg/L) and S. maltophilia (MIC90:0.5 mg/L) with >98% DD agreement. In contrast, A. baumannii exhibited higher MIC values (MIC90:8 mg/L). For A. baumannii, DD agreement dropped to 50% under EUCAST criteria, failing to detect ‘grey zone’ (MIC:1–2 mg/L) isolates. This resulted in 14.3% very major errors. Cefiderocol is effective against P. aeruginosa and S. maltophilia, with reliable DD results. However, for A. baumannii, reduced reliability of DD in the ‘grey zone’ highlights the need for MIC confirmation.