Screening for IEDR MTB clinical isolates. 200 MTB isolates from sputum positive culture were subjected to drug sensitivity assay against INH or EMB. The assay used resazurin as oxidation-reduction indicator. A change in color from blue to pink indicated the growth of bacteria, and the MIC was defined as the minimum drug concentration that prevented the color change in resazurin solution. (A) H37Rv was tested in drug sensitivity assay. Assay was carried out in duplicates at each concentration of streptomycin. The upper panel shows the 24-hour result and the lower panel shows the 48-hour result. Labels were the concentrations of streptomycin in μg/ml after two-fold serial dilution. (B) Upper panel indicates the strain is resistant to both EMB and INH, and the lower panel indicates the strain is resistant to INH but not EMB. Labels were the concentrations of the drug EMB or INH in μg/ml after two-fold serial dilution. Letters in green indicate the normal range of sensitivity. Letters in red indicate clinical level of resistance. (C) A statistical result of drug resistance to INH. Two independent experiments were carried out and representative data were shown. **, p < 0.01.