title: Drug susceptibility testing of Mycobacterium tuberculosis by a nitrate reductase assay applied directly on microscopy-positive sputum samples.
abstract: 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 28days (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.
authors.affiliation: Regional Laboratory of Hygiene, Sfax, Tunisia.
authors.forename: Sana
authors.initials: S
authors.lastname: Kammoun
authors.affiliation: Regional Laboratory of Hygiene, Sfax, Tunisia. Electronic address: smaoui_salma@yahoo.fr.
authors.forename: Salma
authors.initials: S
authors.lastname: Smaoui
authors.affiliation: Regional Laboratory of Hygiene, Sfax, Tunisia.
authors.forename: Chema
authors.initials: C
authors.lastname: Marouane
authors.affiliation: Microbiology Laboratory, Pneumology Hospital, Ariana, Tunisia.
authors.forename: Leila
authors.initials: L
authors.lastname: Slim
authors.affiliation: Regional Laboratory of Hygiene, Sfax, Tunisia.
authors.forename: Férièle
authors.initials: F
authors.lastname: Messadi-Akrout
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D003124:Colorimetry; D003362:Cost-Benefit Analysis; D057075:Enzyme Assays; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology; D008826:Microbial Sensitivity Tests / Q000191:economics / Q000379:methods*; D008853:Microscopy; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D050901:Nitrate Reductase / Q000378:metabolism*; D012293:Rifampin / Q000494:pharmacology; D012680:Sensitivity and Specificity; D013183:Sputum / Q000382:microbiology*; D018088:Tuberculosis, Multidrug-Resistant / Q000188:drug therapy / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D050901:Nitrate Reductase; D007538:Isoniazid; D012293:Rifampin
keywords: Drug resistance; Drug susceptibility testing; M. tuberculosis; Sputum