Identification of Mutations Conferring Tryptanthrin Resistance to <i>Mycobacterium smegmatis</i>

• Main Authors: Svetlana G. Frolova, Ksenia M. Klimina, Ravinder Kumar, Aleksey A. Vatlin, Deepak B. Salunke, Pravin Kendrekar, Valery N. Danilenko, Dmitry A. Maslov
• Format: Article
• Language: English
• Published: MDPI AG 2021-12-01
• Series: Antibiotics
• Subjects: tuberculosis; mycobacterium smegmatis; tryptanthrin; drug resistance; efflux
• Online Access: https://www.mdpi.com/2079-6382/10/1/6

Tuberculosis (TB), caused by <i>Mycobacterium tuberculosis</i>, is a global burden, responsible for over 1 million deaths annually. The emergence and spread of drug-resistant <i>M. tuberculosis</i> strains (MDR-, XDR- and TDR-TB) is the main challenge in global TB-control, requiring the development of novel drugs acting on new biotargets, thus able to overcome the drug-resistance. Tryptanthrin is a natural alkaloid, with great therapeutic potential due to its simple way of synthesis and wide spectrum of biological activities including high bactericidal activity on both drug-susceptible and MDR <i>M. tuberculosis</i> strains. InhA was suggested as the target of tryptanthrins by in silico modeling, making it a promising alternative to isoniazid, able to overcome drug resistance provided by <i>katG</i> mutations. However, neither the mechanism of action of tryptanthrin nor the mechanism of resistance to tryptanthrins was ever confirmed <i>in vitro</i>. We show that the MmpS5-MmpL5 efflux system is able to provide resistance to tryptanthrins using an in-house test-system. Comparative genomic analysis of spontaneous tryptanthrin-resistant <i>M. smegmatis</i> mutants showed that mutations in <i>MSMEG_1963</i> (EmbR transcriptional regulator) lead to a high-level resistance, while those in <i>MSMEG_5597</i> (TetR transcriptional regulator) to a low-level one. Mutations in an MFS transporter gene (<i>MSMEG_4427</i>) were also observed, which might be involved in providing a basal level of tryptanthrins-resistance.