title: Susceptibility of Mycobacterium tuberculosis to first-line antimycobacterial agents in a Brazilian hospital: assessing the utility of the tetrazolium (MTT) microplate assay.
abstract: We conducted a cross-sectional, hospital-based study between January 2006-March 2008 to estimate the resistance of Mycobacterium tuberculosis to first-line drugs in patients with tuberculosis at a Brazilian hospital. We evaluated the performance of the [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide] (MTT) microplate assay compared with the Bactec-MGIT 960 system for mycobacteria testing. The prevalence of resistance in M. tuberculosis was 6.7%. Multidrug-resistance [resistance to rifampicin (RMP) and isoniazid (INH)], INH-resistance and streptomycin (SM)-resistance accounted for 1%, 3.8% and 3.8% of all resistance, respectively, and all isolates were susceptible to ethambutol (EM). The resistance was primary in four cases and acquired in three cases and previous treatment was associated with resistance (p = 0.0129). Among the 119 M. tuberculosis isolates, complete concordance of the results for INH and EM was observed between the MTT microplate and Bactec-MGIT 960TM methods. The observed agreement for RMP was 99% (sensitivity: 90%) and 95.8% for SM (sensitivity 90.9%), lower than those for other drugs. The MTT colourimetric method is an accurate, simple and low-cost alternative in settings with limited resources.
authors.affiliation: Instituto Adolfo Lutz, Secretaria de Saúde do Estado de São Paulo, São Paulo, Brasil.
authors.forename: Michela De Luca
authors.initials: Mde L
authors.lastname: Ferrari
authors.forename: Maria Alice da Silva
authors.initials: MA
authors.lastname: Telles
authors.forename: Lucilaine
authors.initials: L
authors.lastname: Ferrazoli
authors.forename: Carlos Emílio
authors.initials: CE
authors.lastname: Levy
authors.forename: Maria Cecília Barison
authors.initials: MC
authors.lastname: Villares
authors.forename: Maria Luiza
authors.initials: ML
authors.lastname: Moretti
authors.forename: Mariângela Ribeiro
authors.initials: MR
authors.lastname: Resende
mesh_terms: D000328:Adult; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004396:Coloring Agents; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D008297:Male; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009169:Mycobacterium tuberculosis / Q000187:drug effects* / Q000302:isolation & purification; D012189:Retrospective Studies; D013778:Tetrazolium Salts; D013844:Thiazoles; D014376:Tuberculosis / Q000382:microbiology*; D018088:Tuberculosis, Multidrug-Resistant / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D004396:Coloring Agents; D013778:Tetrazolium Salts; D013844:Thiazoles; C022616:thiazolyl blue