Comparison of the susceptibility testing of clinical isolates of Mycobacterium tuberculosis by the XTT colorimetric method and the NCCLS standards method.

The susceptibility or resistance of clinical isolates of Mycobacterium tuberculosis were determined by a method incorporating the 2,3-bis(2-methoxy-4-nitro-5-sulphophenyl)-2H-tetrazolium-5-carboxanilide (XTT) and compared with results obtained by the National Committee for Clinical Laboratory Standards approved standard method (M24-T2). One hundred percent of all isolates demonstrated agreement between the susceptibility and resistance to isoniazid, rifampicin, and ethambutol obtained by the two methods, suggesting that the XTT-based method could provide a useful means for the rapid determination of antimycobacterial susceptibility of clinical isolates of M. tuberculosis.