Molecular Characterization of katG and inhA Mutations by Genotype MTBDRplus Line Probe Assay To Guide Isoniazid and Ethionamide Use for Drug-Resistant Tuberculosis.

Introduction Drug-resistant tuberculosis (TB) continues to be a global health threat in all its forms. Significant resistance has been observed against isoniazid (INH), one of the most important therapeutic options for treating TB. Molecular testing methods such as line probe assay (LPA) provide rapid diagnosis and early management. Mutations in different genes can be detected, which indicate INH and ethionamide (ETH) drug resistance. We aimed to determine the frequency of these mutations in katG and inhA genes by LPA to guide INH and ETH use for drug-resistant TB. Materials and methods Two consecutive sputum samples were collected from each patient, followed by decontamination by N‑acetyl‑L‑cysteine and sodium hydroxide method. LPA was performed on the decontaminated samples by GenoType MTBDR, and the strips were analyzed. Results Out of the 3,398 smear-positive samples tested by LPA, valid results were found in 3,085 (90.79%) samples. Of the 3,085 samples, INH resistance was seen in 295 samples (9.56%), of which mono INH resistance was in 204 samples, and 91 were multidrug resistant. katG S315T was the most common mutation responsible for high-level INH resistance. At the same time, inhA c15t was the most common mutation associated with low-level INH resistance and ETH cross-resistance. The average turnaround time for the processing and reporting of samples was five days. Conclusions The high burden of INH resistance is alarming and can be a major obstacle to TB elimination. Although molecular methods have reduced the reporting time leading to early management of the patients still, a large knowledge gap persists.