The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay is a rapid, cheap, screening test for the in vitro anti-tuberculous activity of chalcones

• No significant difference in the MICs of chalcones in the MABA and the MTT assays.
• The MTT assay is significantly more cost effect than the MABA assay.
• Compound properties are important when choosing a drug susceptibility test method.
• Compound XI (MIC 16 μg/mL) is a promising potential lead chalcone compound.

Rapid and reliable drug susceptibility testing facilitates replenishment of the TB drug pipeline in the fight against drug resistant Mycobacterium tuberculosis. This study compared the performance of the MTT and MABA assays on the anti-tuberculous activity of a set of chalcones. Twenty seven chalcones and chromenochalcones were screened against the laboratory strain M. tuberculosis H37Rv, using a microtitre plate MTT assay at 7 days. The MIC for 20 active compounds was subsequently determined using the MABA, MTT and the Macroscopic broth assays at 7, 14 and 21 days. No significant difference in the MICs, or increase in the MICs was observed over time between the MABA (p = 0.209) and the MTT (p = 0.207) assays, in contrast to the gold standard, the Macroscopic broth assay (p = 0.000). The MICs (16 to > 128 μg/ml) were much higher than the currently used TB drugs. In conclusion, the MTT assay is a cost effective method (R0.06/well) for the rapid in vitro screening of chalcones against M. tuberculosis, producing reliable results in 8 days. The chalcone with a MIC of 16 μg/mL shows promise as a potential lead compound and should be investigated further.