Phenotypic and genotypic methods for detecting multidrug resistance in Mycobacterium tuberculosis.

Abstract

Background. Expeditious charactization of drug susceptibility in Mycobacterium tuberculosis is difficult and, calls for the design and evaluation of faster, cheaper and more effective new techniques.
Objective. The aim of the current study was to compare one genotypic and two phenotypic methods for rapid susceptibility detection of M. tuberculosis.
Material And Methods. Twenty-one M. tuberculosis strains were evaluated by phenotypic methodologies of oxidation and reduction of Alamar blue and MTT in the presence of streptomycin, isoniazid, rifampin and ethambutol. In all tests, the proportion method was applied as the comparison standard. By means of receiver operative characteristic (ROC) analysis, the performance, predictive values and threshold values for all drugs were determined. In addition, the performance of PCR and reverse line blot hybridization in establishing predictive values for sensitivity and resistance were compared in contingency tables.
Results. The susceptibility patterns established by colorimetric techniques were obtained after seven days of incubation. The performances of these tests were excellent for all drugs-the areas under curves were >0.9, 100% of sensitivity (S) and specificity (E) >80%. The genotypic method of RFLP oligotyping detected multidrug resistance with S of 100% and E of 93%. Conclusion. The results indicated that Alamar blue, MTT and RFLP methodologies are rapid and useful tools for characterizing multidrug resistance in M. tuberculosis, particularly for those patients with high risk of developing multidrug resistant tuberculosis.