title: [Evaluation of a colorimetric micromethod for determining the minimal inhibitory concentration of antibiotics against Mycobacterium tuberculosis].
abstract: Multidrug-resistant tuberculosis (MDR) caused by strains resistant to both isoniazid and rifampin is now considered a serious sanitary problem worldwide. New technical tools for the early detection of these strains are urgently needed to avoid their spread within the community. We have evaluated a microplate colorimetric-based method to determine the minimal inhibitory concentration (MIC) of first-line antituberculosis drugs by using 3-(4, 5 dimethylthiazolyl 1-2 yl)-2,5 diphenyl tetrazolium bromide as a bacterial growth indicator (MTT) (M-MTT). A total of 603 clinical isolates, 507 from respiratory cases (84.1%) and 96 from non-respiratory cases (15.9%) were processed. The proportion method on a Löwenstein-Jensen medium (PM) with isoniazid (INH), 0.20 microg/ml; streptomycin (SM), 4.00 microg/ml; ethambutol (EMB), 2.00 microg/ml and rifampin (RMP), 40.00 microg/ml, was used as the gold standard. The drugs and the concentration range tested were: INH, 1.00-0.03 microg/ml; SM, 8.00-0.25 microg/ml; EMB, 32.00-1.00 microg/ml and RMP, 2.00-0.06 microg/ml. MIC results were obtained on an average of 8 days (range: 7-12). The cut-off values for each drug, calculated by the ROC curve method, were: INH, 0.25 microg/ml, RMP, 0.50 microg/ml, SM, 4.00 microg/ml and EMB, 4.00 microg/ml. Sensitivity and specificity for RMP were 100 %, while for INH, they were 97.8% and 99.5% respectively. The results obtained suggested that M-MTT is a low cost and easy to set up method that could be applied to MDR clinical diagnosis in developing countries.
authors.affiliation: Laboratorio de Referencia del Programa de Control de la Tuberculosis de la Provincia de Buenos Aires, Argentina.
authors.forename: M V
authors.initials: MV
authors.lastname: Pontino
authors.forename: B
authors.initials: B
authors.lastname: Di Giulio
authors.forename: C
authors.initials: C
authors.lastname: Fernández
authors.forename: B
authors.initials: B
authors.lastname: Imperiale
authors.forename: A
authors.initials: A
authors.lastname: Bodon
authors.forename: N
authors.initials: N
authors.lastname: Morcillo
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001431:Bacteriological Techniques / Q000379:methods; D006801:Humans; D008826:Microbial Sensitivity Tests; D009169:Mycobacterium tuberculosis / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents