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

Abstract

Cefiderocol is a siderophore-conjugated cephalosporin with potent activity against multidrug-resistant Gram-negative pathogens including Acinetobacter baumannii. The aim of this study was to evaluate cefiderocol testing methods on a relevant collection of 97 Acinetobacter spp. isolates. Commercialized broth microdilution methods (ComASP®, Liofilchem and UMIC®, Bruker), MIC test strips (Liofilchem) and disc diffusion using discs of three different brands (Mast Diagnostic, Liofilchem and Oxoid—Thermo Fisher Scientific) were compared with the broth microdilution reference method. None of the methods tested fulfilled acceptable criteria (essential agreement [EA] ≥ 90%; bias = ±30%) but both BMD methods achieved acceptable categorical agreement rates (CA = 95.9% [93/97, 95% CI 89.9–98.4] and CA = 93.8% [91/97, 95% CI 87.2–97.1] for ComASP® and UMIC®, respectively) and bias < 30% (−7.2% and −25.2% for ComASP® and UMIC®, respectively). The use of MIC gradient testing is strongly discouraged due to misclassification of 55% (n = 23/42) of resistant strains. Finally, the disc diffusion method could be used to rapidly screen for susceptible strains by setting a critical diameter of 22 mm.

Challenges in the Detection of Polymyxin Resistance: From Today to the Future

“…The results obtained by these methods achieved acceptable CA rates of 95.9% for ComASP ® and 93.8% for UMIC ® . However, the EA values were 81.4% for ComASP ® and 78.4% for UMIC ® (acceptable EA values should be greater than 90%) [ 20 ].…”

Cefiderocol and Sulbactam-Durlobactam against Carbapenem-Resistant Acinetobacter baumannii

“…Liu et al [26] observed that disk diffusion was difficult to assess, but the limited isolates that actually exhibited resistance by BMD (CLSI breakpoint) were categorized as susceptible by disk diffusion. Jeannot et al [27] evaluated two commercial BMD methods and discs from three manufacturers, compared with the reference BMD. They showed that none of the tested methods met the accuracy requirements.…”

“…(306 isolates) to FDC was 97.7% using CLSI criteria. Despite the susceptibility testing used, FDC showed excellent in vitro activity against Acinetobacter spp., ABC, and CARB [6,7,[26][27][28].…”