Phenotypic heterogeneity in the isoniazid resistance of isolates with the katG S315 mutation and the term “intermediate” in MGIT 960 testing with EpiCenter (version 5.53) TB eXiST software. (A) Isolate 177836, resistant at 0.1, 1.0, 3.0, and 10.0 mg/liter; (B) isolate 186137, resistant at 0.1, 1.0, and 3.0 mg/liter and intermediate at 10.0 mg/liter; (C) isolate 186069, resistant at 0.1, 1.0, and 3.0 mg/liter and susceptible at 10.0 mg/liter; (D) isolate 176291, resistant at 0.1 and 1.0 mg/liter, intermediate at 3.0 mg/liter, and susceptible at 10.0 mg/liter. Drug concentrations are represented by colors as follows: blue, 0.1 mg/liter; green, 1.0 mg/liter, yellow, 3.0 mg/liter, red, 10.0 mg/liter; black, drug-free growth control.