Isoniazid-Resistant Tuberculosis - A Series of Clinical Cases

The emergence of M. tuberculosis strains resistant to Isoniazid (INH) and Rifampicin (RIF), the two most potent drugs of first-line anti-TB treatment is termed multidrug drug-resistant TB (MDR-TB). Multidrug-resistant tuberculosis has been a severe medical and epidemic problem worldwide.

We present a series of clinical cases consisting of two patients diagnosed with isoniazid-resistant tuberculosis. Histopathological examination supports the diagnosis of tuberculous granulomas. The pathology molecular examination revealed the presence of Isoniazid-resistant Mycobacterium tuberculosis 1, 2 via the following mutation c.947G>A; p. Gly316Asp. Isoniazid-resistance is associated with mutations in the furA-katG and fabG1-inhA operons and in the ahpC gene. 64% of the isoniazid-resistance phenotypes were associated with the kat G 315 mutation worldwide. The second most common mutation is inhA-15, reported in 19% of the Isoniazid-resistant isolates. The significant association between the two mutations, inhA c-15 and kat G 315 respectively, and the high-level resistance is of interest in the interpretation of current and future molecular diagnostic testing, as an early prediction of the level of Isoniazid-resistance is essential to decide the benefit of high-dose Isoniazid use.