Isoniazid resistance in Mycobacterium tuberculosis is a heterogeneous phenotype comprised of overlapping MIC distributions with different underlying resistance mechanisms

Abstract

MIC testing using the BACTEC 960 MGIT system of 70 phylogenetically diverse, isoniazid-resistant clinical strains of Mycobacterium tuberculosis revealed a complex pattern of overlapping MIC distributions. Whole-genome sequencing could explain most of the level of resistance observed. The MIC distribution of strains with only inhA promoter mutations was split by the current concentration that is endorsed by the Clinical Laboratory Standards Institute to detect low-level resistance to isoniazid and is therefore likely not optimally set.