Prepare a 12 mM stock solution by dissolving 5 mg of MTT [3-(4,5dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] in 1 mL of PBS. This stock solution will be enough for 100 reactions (10 µL per reaction). Once prepared, the MTT solution can be stored for 4 wk at 4°C protected from light.

This file is really helpful for baterial MTT assay

http://cshprotocols.cshlp.org/content/2018/6/pdb.rec096875.full?rss=1