Association of pyrazinamide resistance in Mycobacterium tuberculosis with mutations in rpoB, katG, and inhA genes

Multidrug-resistant tuberculosis (MDR-TB) is associated with a high rate of treatment failure. Since the 9 to 11-month shorter oral regimen in MDR-TB treatment includes pyrazinamide (PZA), it is essential to assess the susceptibility of MDR-TB strains to PZA to guide effective therapy. The susceptibility of PZA is highly affected by drug pressure induced by rifampicin (RIF) and isoniazid (INH) resistant strains. This study examines the association between point mutations in the rpoB, katG, inhA, and pncA genes. Resistant patterns of MDR strains were detected through line probe assay. Phenotypic drug susceptibility testing for PZA was performed using MGIT 960 liquid culture for RIF-resistant, INH-resistant, and multidrug-resistant strains. In addition, pncA gene was sequenced to characterize the associated mutation pattern. Out of 780 MTB-positive strains, 195 were found to be resistant to first-line drugs (RIF and/or INH). Among those 195 resistant isolates, 107 (54.87%) were resistant, and 88 (45.12%) were susceptible to PZA. Mutations at S531L in the rpoB gene (RIF), S315T in the katG gene (INH), and C-15T in the inhA gene (INH) were most common (111, 80, and 31, respectively). The highest resistance to PZA was found when all three gene mutations were present in combination (20/23). Out of 24 PZA-resistant strains sequenced pncA gene mutation was found in 23 strains. Significantly high PZA resistance was detected in first-line resistant isolates, and this was much higher in combination mutations. The presence of these mutations predisposes the strain to acquisition of PZA resistance.