Abstract
Aims and objectives: The emergence and spread of multidrug resistant (MDR) Mycobacterium tuberculosis (M. tuberculosis) strains is a critical global health problem. In order to shorten the course of treatment and its effectiveness, it is essential to gain an in-depth insight into the genetic diversity, drug resistance mechanisms and host-pathogen interactions of drug resistant M. tuberculosis. Methods: Between 2014 and 2018, 606 MTBC strains were isolated from 13,892 suspected pulmonary tuberculosis (TB) patients in Tehran, Iran, including 16 MDR-TB cases. A combination of phenotypic (conventional drug susceptibility testing, MIC, Verapamil effectiveness) and genotypic methods (whole-genome sequencing and qPCR) was employed for the identification of additional drug resistances, the role of efflux pumps and strain-to-strain genetic distances as a marker for recent transmission events. Finally, the consequences of mutations in genes encoding the beta subunit of RNA polymerase (rpoB) for host-pathogen interactions was investigated by means of THP-1-derived macrophages infection and Cytokines and Chemokines Real-Time RT2 Profiler PCR Array. Results: MDR and extensively drug-resistant (XDR) TB cases were almost exclusively infected by lineage 2/Beijing strains (14/16, P < 0.001). Out of the 16 MDR/pre-XDR/XDR isolates, 6 (37.5%) and 3 (18.8%) isolates demonstrated a significant decrease in rifampicin (RIF) MIC and isoniazid (INH) MIC due to the Verapamil exposure (64 ÎĽg/mL), respectively. More importantly, it was found that the administration of Verapamil profoundly decreased the MIC of Bedaquiline (BDQ) among most of the studied clinical isolates. Moreover, the efflux pump genes of Rv2938, Rv2936, Rv1145, Rv1146, Rv933, Rv1250, Rv876, Rv2333, Rv2459, Rv849, and Rv1819 were overexpressed in the presence of anti-TB drugs, showing the contribution of these efflux pumps to the overall resistance phenotype. Finally, the macrophages immune responses induced in response to infection with drug-resistant M. tuberculosis (RMR strain) may not be substantially different from drug susceptible M. tuberculosis (H37Rv strain), but the severity of the responses was different in some cases specially IL-6, IL-8, CNTF, IL-13, TNFSF10 and CD40LG in response to RMR and H37Rv strains. In addition, RMR strain showing significantly higher intracellular bacillary growth compared to H37Rv strain. Conclusions: The crucial finding is that almost all of our MDR/pre-XDR/XDR strains are of the Beijing lineage (14/16) and more than half of them are probably from recent transmission (8/14). Our results clearly showed that efflux systems, besides spontaneous mutations, play a role in the development of INH/RIF resistance. In addition, Verapamil was very successful at the phenotypic level specially in response to BDQ. Finally, the results initially demonstrate that the M. tuberculosis carrying the rpoB-S450L can modulate macrophage responses to mediate bacterial survival.
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