title: A microplate indicator-based method for determining the susceptibility of multidrug-resistant Mycobacterium tuberculosis to antimicrobial agents.
abstract: METHODS
  Reference Laboratory, Buenos Aires Province Tuberculosis Control Program, Dr Cetrangolo Hospital, Argentina.
  
  
  OBJECTIVE
  To obtain a rapid, inexpensive method of determining minimal inhibitory concentrations (MIC) of several drugs acting on multidrug-resistant Mycobacterium tuberculosis (MDR-TB), a colorimetric, microplate-based assay (M-MTT) was developed.
  
  
  METHODS
  One hundred and one clinical isolates were studied. Drugs were placed in a microtiter plate, and several two fold dilutions were made in situ. Kanamycin, capreomycin, ethionamide, para-aminosalicylic acid and clarithromycin were tested in a range concentration of 8.0-0.25 microg/ml, cycloserine 60.0-1.9 microg/ml, clofazimine 3.0-0.10 microg/ml, levofloxacin 4.0-0.13 microg/ml and rifabutin 1.0-0.13 microg/ml. General indicator 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) at 5.0 mg/ml was used for visualising cellular growth and viability. The proportion method with Middlebrook 7H11 was used as the gold standard.
  
  
  RESULTS
  MICs by M-MTT were obtained at on average 8 days and correlated with those obtained using the proportion method. In our conditions, the total cost of MIC determination for nine drugs was 5.00 US dollars.
  
  
  CONCLUSIONS
  M-MTT could be used as a simple, rapid, low-cost technology to test the susceptibility of MDR-TB strains to several second-line and alternative drugs, with the objective of orienting future treatment regimens.
authors.affiliation: Reference Laboratory of Buenos Aires Tuberculosis Control Program, Vicente Lopez, Buenos Aires, Argentina. nora_morcillo@fullzero.com.ar
authors.forename: N
authors.initials: N
authors.lastname: Morcillo
authors.forename: B
authors.initials: B
authors.lastname: Di Giulio
authors.forename: B
authors.initials: B
authors.lastname: Testani
authors.forename: M
authors.initials: M
authors.lastname: Pontino
authors.forename: C
authors.initials: C
authors.lastname: Chirico
authors.forename: A
authors.initials: A
authors.lastname: Dolmann
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D004395:Dye Dilution Technique; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D013778:Tetrazolium Salts; D013844:Thiazoles; D017186:Titrimetry / Q000379:methods; D014397:Tuberculosis, Pulmonary / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue