The 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay as rapid colorimetric method for determination of antibiotic susceptibility of clinical Mycobacterium tuberculosis isolates in liquid medium.

We investigated the usefulness of a colorimetric method based on the reduction of a tetrazolium salt (XTT) for the susceptibility testing of clinical isolates of Mycobacterium tuberculosis to isoniazid, rifampin, rifabutin, ethambutol hydrochloride, ethionamide and streptomycin. The isolates and the ATCC reference strains reported as susceptible according to the agar dilution method approved by the National Committee for Clinical Laboratory Standards were found to be susceptible by the XTT colorimetric assay after times of incubation ranging between three days for rifampin and rifabutin to eight days for isoniazid. In comparison with other colorimetric methods reviewed in this article, the proposed assay is suitable for determining the susceptibility or resistance to most antituberculous drugs and, as a consequence of the water-solubility of the formazan yielded by reduction of XTT, additional steps such as the addition of extraction buffer and further incubation before the spectrophotometric analysis are not needed. The XTT reduction assay is an inexpensive, rapid and reliable screening method for the detection of susceptible, resistant and multidrug-resistant strains of M. tuberculosis and is an alternative to the costly performance of molecular or radiometric methods.

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.

Synthesis and antimycobacterial activity of new S-alkylisothiosemicarbazone derivatives.

A new series of S-alkylisothiosemicarbazones of 3- and 4-pyridincarboxaldehyde and 4-fluoro- and 4-trifluoromethylbenzaldehyde was synthesized and evaluated for biological activity against various Mycobacterium strains. Inhibitory activity against Mycobacterium tuberculosis H37Rv ATCC 27294 and INH-R ATCC 35822 was compared with activity against clinical isolated Mycobacteria as well as against MOTT. Some of newly prepared compounds showed best inhibitory values against clinical isolated Mycobacteria, besides to low citotoxicity values.