Figure 1. Schematic representation of exposure of strain H37Rv to 0.1 µg/ml INH using the BACTEC™ MGIT™ 960 and characterization assays performed at selected points.

For each strain, exposure to INH was done in duplicate, in two independent assays - processes A and B. INH(a): exposure process A; INH(b): exposure process B; INH: isoniazid; EI: efflux inhibitor. Vertical arrows represent transfer to new MGIT tubes containing 0.1 µg/ml INH. Seq: nucleotide sequence determination for specific fragments of the genes involved in the resistance to INH; AST: susceptibility testing to all first line antibiotics. MIC_INH: minimum inhibitory concentration determination of isoniazid. Note: This same procedure, here depicted as an example, was carried out for isoniazid exposure of each strain involved in this study.