A multicenter performance evaluation of cefiderocol MIC results: ComASP in comparison to CLSI broth microdilution

The performance of the Liofilchem Compact Antimicrobial Susceptibility Panel (ComASP) Cefiderocol was evaluated in a multicenter study. Enterobacterales, Acinetobacter baumannii, and Pseudomonas aeruginosa clinical isolates and challenge isolates were tested by three and one sites, respectively. Minimum inhibitory concentration (MIC) testing was performed by the Clinical and Laboratory Standards Institute (CLSI) broth microdilution and ComASP, which included two reading endpoints (CLSI read; MIC is the first well in which reduction of growth is <1 mm or light haze/faint turbidity] and ComASP [ComASP read; MIC is the first well at which 100% inhibition of growth occurs]). Each site performed reproducibility and quality control (QC) by ComASP and broth microdilution (BMD). Reproducibility was excellent (97.4% within ±1 dilution of modal MIC). All QC results were within CLSI QC ranges by BMD and ComASP, except for two E. coli ATCC 25922 results from one site. Essential agreement for combined clinical and challenge Enterobacterales was 84.3% (CLSI read) and 95.7% (ComASP read), P. aeruginosa was 83.3% (CLSI read) and 93.7% (ComASP read), and A. baumannii was 78.3% (CLSI read) and 96.7% (ComASP read). Categorical agreement for Enterobacterales was 92.4% for both CLSI read and ComASP read, for P. aeruginosa was 89.7% (CLSI read) and 92.1% (ComASP read), and for A. baumannii was 72.8% (CLSI read) and 91.3% (ComASP read). There were no very major errors using the ComASP read. One very major error for P. aeruginosa occurred using the CLSI read method. Three very major errors for A. baumannii occurred using the CLSI read method. ComASP Cefiderocol was shown to be a reliable method for testing cefiderocol MIC against relevant clinical isolates when ComASP read is used.

There are very limited commercial methods available to clinical laboratories for cefiderocol minimum inhibitory concentration (MIC) testing. The Compact Antimicrobial Susceptibility Panel (ComASP) Cefiderocol method includes iron-depleted cation-adjusted Mueller-Hinton broth, which eliminates variability in cefiderocol MIC results based on iron levels. The lyophilized multi-well format of ComASP also provides for room temperature storage. In comparison to what an individual lab may do for method verification, this multi-site, multi-isolate study provides a robust evaluation and greater assurance to clinical microbiologists of the method's accurate and reproducible performance.