Detection of isoniazid and rifampin resistance in Mycobacterium tuberculosis strains by single-strand conformation polymorphism analysis and restriction fragment length polymorphism.

Anti-Mycobacterium tuberculosis drug-resistance, mainly multi-drug resistance (MDR-TB), represents an important public health problem in several countries. Aim of our study is to identify the presence of these mutations in M. tuberculosis isoniazid- and rifampin-resistant strains isolated in our Institute; to evaluate linkage between type of mutation and level of resistance; to determine the usefulness of easy molecular techniques for rapid detection of such mutations on body specimens. Isoniazid- and rifampin-resistance was tested on 67 M. tuberculosis strains by Single-Strand Conformation Polymorphism (SSCP) and Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) assays, using HaeIII, PstuI, BsteII, BstuI enzymes. Drug-resistance of control strains was determined by cultural techniques (fluorimetry- BACTEC 9120). Cultural assay showed isoniazid- and rifampin-resistance in 6.12 and 2%, respectively (data confirmed by SSCP assay). Mutation of katG, linked to isoniazid resistance, was detected using BstuI enzyme, and mutation of rpoB, expression of reduced sensitivity to rifampin, using HaeIII. 15 body specimens, M. tuberculosis-positive to conventional assays, were tested by SSCP technique. Epidemiologic reports of numerous cases of tuberculosis due to MDR strains induce to detect quickly both Mycobacteria and drug-resistance, in order to start prompt effective therapy. On this basis, molecular assays are useful for a rapid therapeutic decision.