Abstract: Objective To use the ability of viable cells to reduce 34,5dimethylthiazol2yi2,5diphenyltetrazolium bromide(MTT)to set up a test to detect 4 antimycobacterial drugs'influence on viability of invitro cultured BCG.Method To detect different concentration of 4 antimycobacterial drugs—Rifampin,Streptomycin,Isoniazid and Paminosalicylic acid's viability influent level in BCG.Result The assay shows a linear relationship between the number of vibable bacteria and the ability to reduce MTT.BCG exposed to antimycobacterial drugs showed concentrationdependent inhibition of the ability to reduce MTT.The inhibition paralleled the reduction in the number of colony forming units(CFU).Conclusion The assay can be visually read and requires less than 3 days to obtain susceptibility results.It is a cheap and rapid screening method for BCG vitality and be possible a cheap and rapid screening method for multidrugresistant M.tuberculosis.

Key words: MTT, Anti_mycobacterial drugs, BCG viability, Detection