RESUMEN
Current methods for drug susceptibility testing [DST] of Mycobacterium tuberculosis [MTB] are either costly or slow. As the prevalence of multidrug-resistant [MDR] strains increases, the need for fast, reliable, and inexpensive methods is obvious. This study evaluated a rapid colorimetric nitrate reductase assay [NRA] for direct DST of MTB directly from clinical sputum samples. A total of 111 sputa with positive microscopy results for acid-fast bacilli [AFB] with more than 10 AFB per high-power field were used in the study. The samples were decontaminated using the modified Petroff method. The NRA results were compared with the reference indirect proportion method. The sensitivity and the specificity of the direct NRA were 90% and 97.3%, 92.6% and 98.2%, 52.9% and 100%, and 28.6% and 100% for rifampin, isoniazid, streptomycin, and ethambutol, respectively. The results were in most cases available in 28 days [84.3%]. The direct NRA could be used as a rapid, inexpensive, and accurate method to determine rifampin and isoniazid susceptibility directly from sputum. The technique might become a valid alternative to traditional methods, especially in low-income countries
RESUMEN
The use of molecular techniques is a major improvement for the rapid routine detection and control of multidrug-resistant tuberculosis [MDR-TB]. In this study, the multiplex allele-specific polymerase chain reaction [MAS-PCR] was developed to simultaneously detect the most frequent mutations associated with isoniazid [INH] and rifampin [RIF] resistance in a single assay. The assay was tested with 53 clinical isolates. Among them, 27 were MDR strains, 17 were mono-resistant to INH, one was mono-resistant to RIF, and eight were susceptible. The MAS-PCR assay showed a specificity of 100% in detecting drug resistance. An equivalent sensitivity of 92.6% in detecting MDR and RIF-resistance was found. The sensitivity for the detection of INH-resistance was 88.6%. The MAS-PCR assay was a simple and rapid method for detecting the INH and RIF-resistance in Mycobacterium tuberculosis [MT] clinical strains. It is also easy to perform and to interpret. The assay is inexpensive and a less-demanding technique