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. 2024 Aug 22;23(1):78.
doi: 10.1186/s12941-024-00731-1.

Commercially available tests for determining cefiderocol susceptibility display variable performance in the Achromobacter genus

Vincent Jean-Pierre  1 , Pauline Sorlin  2 , Katy Jeannot  3 , Raphaël Chiron  4 , Jean-Philippe Lavigne  5 , Alix Pantel  5 , Hélène Marchandin  6
Affiliations

Commercially available tests for determining cefiderocol susceptibility display variable performance in the Achromobacter genus

Vincent Jean-Pierre et al. Ann Clin Microbiol Antimicrob. .

Abstract

Background: Cefiderocol is a siderophore-conjugated cephalosporin increasingly used in the management of Achromobacter infections. Testing for cefiderocol susceptibility is challenging with distinct recommendations depending on the pathogens.

Objectives: We evaluated the performance of commercial tests for testing cefiderocol susceptibility in the Achromobacter genus and reviewed the literature.

Methods: Diffusion (disks, MIC gradient test strips [MTS], Liofilchem) and broth microdilution (BMD) methods (ComASP™, Liofilchem; UMIC®, Bruker) were compared with the BMD reference method according to the EUCAST guidelines on 143 Achromobacter strains from 14 species with MIC50/90 of ≤ 0.015/0.5 mg/L. A literature search was conducted regardless of method or species.

Results: None of the methods tested fulfilled an acceptable essential agreement (EA). MTS displayed the lowest EA (30.8%) after UMIC® (49%) and ComASP™ (76.9%). All methods achieved an acceptable bias, with MICs either underestimated using MTS (-1.3%) and ComASP™ (-14.2%) or overestimated with UMIC® (+ 9.1%). Inhibition zone diameters ranged from 6 to 38 mm (IZD50/90=33/30 mm). UMIC® and ComASP™ failed to categorize one or the two cefiderocol-resistant strains of this study as resistant unlike the diffusion-based methods. The literature review highlighted distinct performance of the available methods according to pathogens and testing conditions.

Conclusions: The use of MTS is discouraged for Achromobacter spp. Disk diffusion can be used to screen for susceptible strains by setting a threshold diameter of 30 mm. UMIC® and ComASP™ should not be used as the sole method but have to be systematically associated with disk diffusion to detect the yet rarely described cefiderocol-resistant Achromobacter sp. strains.

Keywords: Achromobacter; Cefiderocol; Diffusion; Disk; Microdilution; Susceptibility testing.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Fig. 1
Fig. 1
Correlation between cefiderocol MICs determined by the reference BMD method and by commercial methods (a) ComASP™, (b) UMIC® and (c) MTS. MTS assays were performed on unsupplemented MH II agar plates (Liofilchem). The number of strains with MIC determined by the commercial method corresponding to the BMD method, ± one 2-fold dilution, ± two 2-fold dilution, ± three 2-fold dilution and ≥ ± four 2-fold dilution compared to the reference MIC, are highlighted in dark grey, light grey, light orange, dark orange and white areas, respectively. BMD: broth microdilution; MIC: minimal inhibitory concentration.
Fig. 2
Fig. 2
Distribution of the cefiderocol MICs (mg/L) or IZDs (mm) determined by several methods for 143 Achromobacter strains according to species. (a) BMD reference method, (b) ComASP™, (c) UMIC®, (d) Liofilchem MTS, (e) Liofilchem disks. Disk and MTS assays were performed on unsupplemented MH II agar plates (Liofilchem). BMD: broth microdilution; IZD: inhibition zone diameter; MIC: minimal inhibitory concentration
See this image and copyright information in PMC

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