Rapid, Low-Technology MIC Determination with Clinical <i>Mycobacterium tuberculosis</i> Isolates by Using the Microplate Alamar Blue Assay

TLDR

The MABA is a simple, rapid, low‑cost assay that uses a nontoxic, temperature‑stable reagent and requires no expensive instrumentation. The authors used a colorimetric microplate Alamar Blue assay to determine MICs of INH, rifampin, streptomycin, and ethambutol for 34 Peruvian M. tuberculosis isolates and H37Rv, using bacterial suspensions prepared directly from solid media.

Abstract

A colorimetric, microplate-based Alamar Blue assay (MABA) method was used to determine the MICs of isoniazid (INH), rifampin, streptomycin (SM), and ethambutol (EMB) for 34 Peruvian Mycobacterium tuberculosis isolates (including both pansensitive and multidrug-resistant strains) and the H37Rv strain by using bacterial suspensions prepared directly from solid media. Results for all isolates were available within 8 days. 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 BACTEC 460 system were 87.9% for initial results and 93.6% after retesting 12 of 17 samples with discrepant results. Interpretation of MABA endpoints improved with technical experience. The MABA is a simple, rapid, low-cost, appropriate technology which does not require expensive instrumentation and which makes use of a nontoxic, temperature-stable reagent.