 On the other hand, the accuracy of the MTT microdilution assay can be compromised by samples that are coloured (such as plant extracts), redox active and/or samples that are not soluble in the medium, which is predominantly aqueous.Although more toxic solvents such as methanol or acetone can be used for water-insoluble compounds (no more that 2% final concentration), DMSO is a popular alternative due to its comparatively lower toxicity.Regardless of the solvent used, some of the compounds might still precipitate which will reduce interaction between the sample tested and the bacteria and as a result limit the sample activity.