Towards clinical breakpoints for non-tuberculous mycobacteria – Determination of epidemiological cut off values for the Mycobacterium avium complex and Mycobacterium abscessus using broth microdilution

EUCAST AMST study group, ESCMYC study group, Miguel Viveiros, Diana Machado

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15 Citations (Scopus)
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Abstract

Objective: For non-tuberculous mycobacteria (NTM), minimum inhibitory concentration (MIC) distributions of wild-type isolates have not been systematically evaluated despite their importance for establishing antimicrobial susceptibility testing (AST) breakpoints. Methods: We gathered MIC distributions for drugs used against the Mycobacterium avium complex (MAC) and Mycobacterium abscessus (MAB) obtained by commercial broth microdilution (SLOMYCOI and RAPMYCOI) from 12 laboratories. Epidemiological cut-off values (ECOFFs) and tentative ECOFFs (TECOFFs) were determined by EUCAST methodology including quality control (QC) strains. Results: The clarithromycin ECOFF was 16 mg/L for M. avium (n = 1271) whereas TECOFFs were 8 mg/L for M. intracellulare (n = 415) and 1 mg/L for MAB (n = 1014) confirmed by analysing MAB subspecies without inducible macrolide resistance (n = 235). For amikacin, the ECOFFs were 64 mg/L for MAC and MAB. For moxifloxacin, the WT spanned >8 mg/L for both MAC and MAB. For linezolid, the ECOFF and TECOFF were 64 mg/L for M. avium and M. intracellulare, respectively. Current CLSI breakpoints for amikacin (16 mg/L), moxifloxacin (1 mg/L) and linezolid (8 mg/L) divided the corresponding WT distributions. For QC M. avium and M. peregrinum, ≥95% of MIC values were well within recommended QC ranges. Conclusion: As a first step towards clinical breakpoints for NTM, (T)ECOFFs were defined for several antimicrobials against MAC and MAB. Broad wild-type MIC distributions indicate a need for further method refinement which is now under development within the EUCAST subcommittee for anti-mycobacterial drug susceptibility testing. In addition, we showed that several CLSI NTM breakpoints are not consistent in relation to the (T)ECOFFs.

Original languageEnglish
Pages (from-to)758-764
Number of pages7
JournalClinical Microbiology and Infection
Volume29
Issue number6
DOIs
Publication statusPublished - Jun 2023

Keywords

  • Broth microdilution
  • Drug susceptibility testing
  • ECOFF
  • Mycobacterium
  • Mycobacterium abscessus
  • Mycobacterium avium
  • Non-tuberculous mycobacteria

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