Simple procedure for drug susceptibility testing of Mycobacterium tuberculosis using a commercial colorimetic assay

The aim of this study was to evaluate a simple method using a commercial colorimetric assay (Alamar Blue Oxidation-Reduction Indicator; Accumed, USA) in a microtiter format for testing the susceptibility of 94 strains of Mycobacterium tuberculosis to isoniazid, rifampicin, ethambutol and streptomycin. The method makes use of one critical concentration of each drug, and the results are available within 8-10 days. Overall, 97.1% agreement with the proportion method was obtained. Full agreement was obtained for isoniazid and rifampicin. The method is simple to perform, permits visual reading of results, and is practicable for laboratories with limited resources.