Performance of discs, sensititre EUMDROXF microplates and MTS gradient strips for the determination of the susceptibility of multidrug-resistant Pseudomonas aeruginosa to cefiderocol

Disc Diffusion and ComASP® Cefiderocol Microdilution Panel to Overcome the Challenge of Cefiderocol Susceptibility Testing in Clinical Laboratory Routine

“…Lyophilized panels (Sensititre TM , ThermoFisher Scientific, Waltham, MA, USA) containing scalar concentrations of cefiderocol and a proprietary chelator in the wells bypassed the requirement for ID-CAMHB. First evaluations showed that Sensititre TM panels were substantially equivalent to reference broth microdilution and received FDA clearance [ 18 , 19 , 20 ]. In August 2022, EUCAST evaluated the commercially available tests for cefiderocol susceptibility reporting that all presented problems related to accuracy, reproducibility, bias and/or for some, skipped wells.…”

Performance of the Disc Diffusion Method, MTS Gradient Tests and Two Commercially Available Microdilution Tests for the Determination of Cefiderocol Susceptibility in Acinetobacter spp.

“…Disc diffusion assays were carried out following the EUCAST guidelines (https://eucast.org/ (accessed on 21 June 2023)) with cefiderocol discs loaded at 30 micrograms from 3 manufacturers (Mast Diagnostic, Merseyside, UK; Liofilchem, Roseto degli Abruzzi, Italy; and Oxoid-Thermo Fisher Scientific, Basingstoke, UK) and Becton Dickinson MHA. This latter was chosen because the inhibition zone diameters for the P. aeruginosa ATCC 27853 quality control strain in previous study were within the acceptable range for this MHA manufacturer [10,17]. Colonies within inhibition zones were taken into account and diameters were measured independently by 3 operators and interpreted according to the recommendations of the EUCAST (strain categorized as susceptible if inhibition zone diameter ≥ 17 mm and resistant if inhibition zone diameter < 17 mm).…”

“…Reference MIC values were determined using an iron-depleted and cation-adjusted Mueller–Hinton broth (ID-CAMHB) and a titrated powder of cefiderocol (MedChemExpress, Sollentuna, Sweden) as described previously and according to the recommendation of the Clinical and Laboratory Standards Institute [ 10 , 16 ]. Briefly, a commercial Mueller–Hinton broth (Becton Dickinson, Le Pont-de-Claix, France) was treated with a Chelex resin (Bio-Rad Laboratories, Hercules, CA, USA) and then supplemented with divalent cations (Mg 2+ , Ca 2+ , Zn 2+ ).…”

“…Other susceptibility testing methods have been successively commercialized, including MIC test strips (MTS) and discs, which can be used with regular Mueller–Hinton agar (MHA), and UMIC ® and ComASP ® microplates using ID CA-MHB. The performance of some of those methods has been evaluated for Enterobacterales and Pseudomonas aeruginosa , showing that microplates should be an alternative to the reference BMD method and that MIC strips may not be used [ 10 , 11 ]. In addition, several sources reported large variations in inhibitory zone diameters, depending on the disc and MHA brands, for QC and clinical strains [ 10 , 12 ].…”

“…The performance of some of those methods has been evaluated for Enterobacterales and Pseudomonas aeruginosa , showing that microplates should be an alternative to the reference BMD method and that MIC strips may not be used [ 10 , 11 ]. In addition, several sources reported large variations in inhibitory zone diameters, depending on the disc and MHA brands, for QC and clinical strains [ 10 , 12 ]. Cefiderocol susceptibility testing appears particularly tricky in A. baumannii regarding the reproducibility and accuracy of both cefiderocol BMD and disc diffusion methods [ 13 , 14 ].…”