Identification of a Mycobacterium tuberculosis strain with stable, low-level resistance to isoniazid

We have identified a potential quality control strain of Mycobacterium tuberculosis to monitor isoniazid susceptibility testing. This strain (strain A) has a stable phenotypic low-level resistance to isoniazid, has a mutation of C (-15) --> T in the inhA promoter region, and gave consistent susceptibility test results in 141 laboratories.