科研之友
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摘要
background: knowledge of the rates of drug resistance is one of the pillars of tuberculosis control program evaluation. data from low-resource countries are scarce and results are delayed due to the techniques employed. there is therefore an urgent need for evaluation of faster and less onerous testing methods. objective: to compare the performance of rapid colorimetric assays for phenotyping that employ oxidation-reduction indicators to determine the susceptibility profile of mycobacterium tuberculosis with the gold-standard proportion method on lowenstein-jensen medium. method: we analyzed 166 m. tuberculosis strains of known susceptibility. minimal inhibition concentrations for isoniazid and rifampicin were determined in microplates, using a liquid medium and alamar blue and tetrazolium bromide indicators. to measure agreement the kappa value was used. cutoff values between sensitive and resistant strains were defined as 0.2mg/ml and 1.0mg/ml for isoniazid and rifampicin, respectively. results: there was 100% concordance between alamar blue and tetrazolium bromide methods in the determination of minimal inhibition concentrations. agreement between the colorimetric method and the lowenstein-jensen was 95% for isoniazid and rifampicin. using the colorimetric method, results were obtained within 7 days, in contrast to the 28 days required for the conventional method. conclusions: assays to determine minimal inhibition concentrations in liquid medium and employing oxidation-reduction indicators proved to be rapid and inexpensive. this method has the potential to become a faster, alternative method for determining susceptibility of m. tuberculosis strains in developing countries.
