Evaluation of wild-type MIC distributions as a tool for determination of clinical breakpoints for Mycobacterium tuberculosis.

Objectives: The aim of this study was to establish wild-type MIC distributions of first-line drugs for Mycobacterium tuberculosis, as well as to explore the usefulness of such distributions when setting clinical breakpoints.

Methods: We determined the MICs of rifampicin, isoniazid and ethambutol for M. tuberculosis using a Middlebrook 7H10 dilution method for 90 consecutive clinical isolates, 8 resistant strains and 16 isolates from the WHO proficiency test panel.