title: Nitrate reductase assay for the rapid detection of pyrazinamide resistance in Mycobacterium tuberculosis using nicotinamide.
abstract: OBJECTIVE
  The purpose of this study was to develop the nitrate reductase assay (NRA) for the rapid detection of pyrazinamide resistance in Mycobacterium tuberculosis using nicotinamide resistance as a marker of pyrazinamide resistance in Löwenstein-Jensen (LJ) medium at neutral pH.
  
  
  METHODS
  We tested 68 M. tuberculosis isolates using nicotinamide at three different concentrations (1000, 500 and 250 mg/L) by the NRA in LJ medium and compared the results with those obtained with the BACTEC 460-TB or the BACTEC MGIT 960 as reference standard methods. Mutations in the pncA gene were detected by DNA sequencing of the pyrazinamide-resistant isolates.
  
  
  RESULTS
  Out of 34 M. tuberculosis pyrazinamide-resistant isolates, 31 were found to be resistant to 1000 and 500 mg/L nicotinamide giving sensitivity and specificity of 91% and 94%, respectively. At 250 mg/L nicotinamide, the sensitivity and specificity decreased to 91% and 71%, respectively. Results were obtained in an average of 10 days. Based on these results, a tentative breakpoint concentration of 500 mg/L nicotinamide was defined. DNA sequencing of the pncA gene detected mutations in 26 out of 34 M. tuberculosis isolates resistant to pyrazinamide.
  
  
  CONCLUSIONS
  The NRA using nicotinamide to detect resistance to pyrazinamide in LJ medium is a rapid and accurate method that could be useful in limited-resource countries where the BACTEC 460-TB or the BACTEC MGIT 960 system is not available.
authors.affiliation: Mycobacteriology Unit, Institute of Tropical Medicine, Nationalestraat 155, Antwerp 2000, Belgium. amartin@itg.be
authors.forename: Anandi
authors.initials: A
authors.lastname: Martin
authors.forename: Andrés
authors.initials: A
authors.lastname: Cubillos-Ruiz
authors.forename: Andrea
authors.initials: A
authors.lastname: Von Groll
authors.forename: Patricia
authors.initials: P
authors.lastname: Del Portillo
authors.forename: Françoise
authors.initials: F
authors.lastname: Portaels
authors.forename: Juan Carlos
authors.initials: JC
authors.lastname: Palomino
mesh_terms: D000995:Antitubercular Agents / Q000494:pharmacology*; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects* / Q000235:genetics; D005798:Genes, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D008969:Molecular Sequence Data; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000201:enzymology; D009536:Niacinamide / Q000494:pharmacology*; D050901:Nitrate Reductase / Q000378:metabolism*; D011718:Pyrazinamide / Q000494:pharmacology*; D013997:Time Factors; D018088:Tuberculosis, Multidrug-Resistant / Q000188:drug therapy / Q000382:microbiology
chemical_list: D000995:Antitubercular Agents; D004269:DNA, Bacterial; D009536:Niacinamide; D011718:Pyrazinamide; D050901:Nitrate Reductase