RAPID, LOW-TECHNOLOGY MIC DETERMINATION WITH CLINICAL MYCOBACTERIUM-TUBERCULOSIS ISOLATES BY USING THE MICROPLATE ALAMAR BLUE ASSAY

A colorimetric, microplate-based Alamar Blue assay (MABA) method was u sed to determine the MICs of isoniazid (INH), rifampin, streptomycin ( SM), and ethambutol (EMB) for 34 Peruvian Mycobacterium tuberculosis i solates (including both pansensitive and multidrug-resistant strains) and the H(37)Rv strain by using bacterial suspensions prepared directl y from solid media, Results for all isolates were available within 8 d ays, Discordant results were observed on initial tests for 3 of 16 INH -susceptible isolates, 5 of 31 EMB-susceptible isolates, and 2 of 4 SM -resistant isolates (by the BACTEC 460 system), The overall agreements between the MICs obtained by MABA and the results obtained with the B ACTEC 460 system were 87.9% for initial results and 93.6% after retest ing 12 of 17 samples with discrepant results, Interpretation of MABA e ndpoints improved with technical experience, The MABA is a simple, rap id, low-cost, appropriate technology which does not require expensive instrumentation and which makes use of a nontoxic, temperature-stable reagent.