[A simple enzyme test for proving the resistance to isoniazid of Mycobacterium tuberculosis strains]

Resistance to isoniazid is the consequence of mutation in some genes or genomic sequences. One of them is katG gene, which encode catalase-peroxidase. The activity of this enzyme can be revealed by simultaneous test catalase-peroxidase. The aim of the study was to assess the correlation between the results of catalase-peroxidase test and isoniazid- resistance of M. tuberculosis strains, in order to estimate the utility of this test in current practice. Material and method. We assessed the results of catalase- peroxidase test of 2268 identified M. tuberculosis strains (19 isolated from silicotuberculosis patients, 198 isolated from industrial dust and chemical polluted city patients, and 2051 strains isolated from other pulmonary tuberculosis patients), with known pattern of susceptibility/resistance. Six hundred twenty four strains (27.5%) had been INH mono-resistant or INH resistant associated with other resistance. It resulted a significant correlation between INH resistance and the negative result of catalase-peroxidase test (p <0.001). More than that, the negative result of peroxidase test was obtained in 63.5% of INH resistant strains. This simple and easy to do test, used for the strains after growth in primary culture, can he helpful in order to confirm the suspicion of INH resistance.