Drug susceptibility testing of Mycobacterium tuberculosis by a nitrate reductase assay applied directly on microscopy-positive sputum samples.
Current methods for drug susceptibility testing of Mycobacterium tuberculosis are either costly or slow. As the prevalence of multidrug-resistant strains increases, the need for fast, reliable, and inexpensive methods that can also be applied in settings with scarce resources is obvious. We evaluated a rapid colorimetric nitrate reductase assay (NRA) for direct drug susceptibility testing of M. tuberculosis directly from clinical sputum samples with positive microscopy results for acid-fast bacilli with more than 10 acid-fast bacilli per high-power field. We have saved valuable time by omitting the preisolation step. The sensitivity (ability to detect true drug resistance) and specificity (ability to detect true drug susceptibility) of the direct NRA, using the direct proportion method as the reference, were 100 and 100%, 93 and 100%, 76 and 100%, and 55 and 99% for rifampin, isoniazid, streptomycin, and ethambutol, respectively, when tested on M. tuberculosis strains present in 121 samples. The results were in most cases available in 14 days. 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.
Musa
Humberto R
HR
Laboratorio de Micobacteriología, Hospital F. J. Muñiz, Buenos Aires, Argentina. humbertomusa@hotmail.com
Ambroggi
Marta
M
Souto
Alejandro
A
Angeby
K A Kristian
KA
D000995:Antitubercular Agents / Q000494:pharmacology*; D001118:Argentina; D003124:Colorimetry; D024881:Drug Resistance, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D008853:Microscopy; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D013997:Time Factors; D014397:Tuberculosis, Pulmonary / Q000382:microbiology*
D000995:Antitubercular Agents; D009565:Nitrate Reductases; D050901:Nitrate Reductase