Multicentre testing of the EUCAST broth microdilution reference method for MIC determination on Mycobacterium tuberculosis

Thomas Schön, Jim Werngren, Diana Machado, Emanuele Borroni, Maria Wijkander, Gerard Lina, Johan Mouton, Erika Matuschek, Gunnar Kahlmeter, Christian Giske, Miguel Santin, Daniela Maria Cirillo, Miguel Viveiros, Emmanuelle Cambau*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Objectives: The first objective of the European Committee on Antimicrobial Susceptibility Testing (EUCAST) subcommittee for antimycobacterial susceptibility testing (AMST), launched in 2016, was to set a reference method for determining the MICs of antituberculous agents, since many protocols are used worldwide and a consensus one is needed for the determination of microbiological breakpoints. Methods: During 2017 and 2018, MIC determination protocols were evaluated prospectively in a multicentre study within the four AMST laboratories. MIC results were obtained for isoniazid, levofloxacin and amikacin on the reference strain Mycobacterium tuberculosis H37Rv ATCC 27294. Broth microdilution (BMD) in Middlebrook 7H9 and solid medium dilution (SMD) in Middlebrook 7H10 were performed using two inoculum concentrations. MICs were interpreted with regard to visual and 99% inhibition after 7, 14 or 21 days of incubation for BMD and 21 days for SMD. Results: Following the EUCAST reference protocol, intra- and inter-assay agreements were within ±1 MIC dilution for >95% of the observations for the three drugs in both methods. MIC values, presented as MIC mode (range) for BMD and SMD respectively, were: 0.03 (0.015–0.06) mg/L and 0.12 (0.06–0.25) mg/L for isoniazid, 0.25 mg/L (0.25–0.5) and 0.5 mg/L (0.12–0.5) for levofloxacin, and 0.5 mg/L (0.5–1.0) and 0.5 mg/L (0.5–1.0) for amikacin. Conclusions: Both SMD and BMD were reproducible and eligible as a reference method for MIC determination of the Mycobacterium tuberculosis complex (MTBC). BMD was finally selected as the EUCAST reference method. From now on it will be used to set epidemiological cut-off values and clinical breakpoints of new and old antituberculous agents.

Original languageEnglish
Pages (from-to)288.e1-288.e4
JournalClinical Microbiology and Infection
Issue number2
Publication statusPublished - Feb 2021

Bibliographical note

Funding Information:
All authors declare no conflict of interest regarding this study. This study was supported by a grant from ESCMID to the study group ESGMYC (ESCMID study group on mycobacterial infections) 2017-2019.

Publisher Copyright: © 2020 The Authors

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  • EMC OR-01


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