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Performance of disc diffusion, MIC gradient tests and Vitek 2 for ceftolozane/tazobactam and ceftazidime/avibactam susceptibility testing of Pseudomonas aeruginosa

Abstract : Abstract Objectives To assess performance of disc diffusion, gradient tests and Vitek 2 system to determine the susceptibility of clinical Pseudomonas aeruginosa strains to ceftolozane/tazobactam (C/T) and ceftazidime/avibactam (CZA). Methods Two-hundred non-duplicate P. aeruginosa strains isolated by 47 French medical laboratories were selected to cover a wide range of C/T and CZA MICs. Performance of C/T disc (30/10 μg, Bio-Rad), CZA discs (10/4 μg) (Thermo Fisher and Bio-Rad), C/T and CZA gradient tests (Etest, BioMérieux; MIC Test Strip, Liofilchem), and AST-XN12 card of Vitek 2 system (BioMérieux) were compared with a broth microdilution (BMD) method (Thermo Fisher). MIC and disc results were interpreted using current EUCAST breakpoints. Results Twenty percent and 17% of strains were resistant to C/T and CZA, respectively. All the methods tested satisfactorily determined the susceptibility of P. aeruginosa to C/T [Category Agreement (CA) ≥95%] except the disc diffusion method. Because of the high rates of Major Errors (MEs) (12.5%), this latter method tends to overestimate the resistance. For CZA, only the gradient tests yielded more than 90% of CA. The Vitek 2 system and disc diffusion misclassified 18.1%, 10.1% (disc Bio-Rad) and 11.9% (disc Thermo Fisher) of susceptible strains, respectively. Conclusions The gradient tests (MIC Test Strip and Etest) and Vitek 2 card XN12 performed the best to determine the susceptibility of P. aeruginosa to C/T, whereas gradient tests were an acceptable alternative to BMD to assess CZA susceptibility.
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Submitted on : Thursday, December 16, 2021 - 1:58:33 PM
Last modification on : Thursday, January 13, 2022 - 11:58:09 AM

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Brice Daragon, Damien Fournier, Patrick Plésiat, Katy Jeannot. Performance of disc diffusion, MIC gradient tests and Vitek 2 for ceftolozane/tazobactam and ceftazidime/avibactam susceptibility testing of Pseudomonas aeruginosa. Journal of Antimicrobial Chemotherapy, Oxford University Press (OUP), 2021, 76 (10), pp.2586-2592. ⟨10.1093/jac/dkab236⟩. ⟨hal-03483278⟩

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