Genotypic Characterization of <i>katG</i>, <i>inhA</i>, and <i>ahpC</i> in Isoniazid-Resistant <i>Mycobacterium tuberculosis</i> Clinical Isolates in Shanghai, China

Abstract

Background: Mycobacterium tuberculosis is a pathogen that causes Tuberculosis and can invade various organs in infected patients. Its high morbidity and high mortality seriously threaten human health. In recent years, the continuous emergence of drug-resistant Tuberculosis bacteria has brought severe challenges to the prevention and control of Tuberculosis. Objectives: This study aimed to characterize the most frequent mutations of the katG, inhA, and ahpC genes in isoniazid (INH)-resistant M. tuberculosis clinical isolates in Shanghai Pulmonary Hospital, China, and investigate the relationship between gene mutations and the minimum inhibitory concentrations (MICs) of INH against M. tuberculosis. Methods: We collected 92 INH-resistant and 30 INH-susceptible clinical isolates of M. tuberculosis. The drug resistance profiles of M. tuberculosis clinical isolates against common anti-tuberculosis drugs were determined and sequencing analysis was performed. Results: Of 92 INH-resistant strains, mutations in the katG and inhA genes were observed in 64 (69.6%) isolates and five (5.4%) isolates, respectively, and only had one (1.1%) strain both katG and inhA mutations. Among them, 62 (67.4%) strains carried a single mutation at codon 315 of the katG gene and a new mutation site was found in the katG gene of two strains. We detected a single mutation site at codon 271 and three simultaneous mutation sites at codons 315, 431, and 439. Only one (3.3%) of the 30 isoniazid-sensitive strains had the katG mutation. The AhpC mutation was detected in no experimental strains. The KatG Ser 315 Thr (AGC315ACC) mutation occurred in 53 (68.8%) out of 77 strains with high MICs (≥ 1 g/mL) of isoniazid-resistant M. tuberculosis while five (33.3%) out of 15 strains with low MICs (less than 1 g/mL) had katG Ser 315 Thr (AGC315ACC) mutation. Conclusions: Isoniazid-resistant strains were dominated by Ser315 → Thr (AGC → ACC) substitution, which seems to be associated with multidrug resistance and high-level resistance to INH. Multisite mutations are related to multidrug-resistant M. tuberculosis and the discovery of new mutation sites provides a new basis for the detection of drug-resistant M. tuberculosis.