Molecular characterization of para-aminosalicylic acid resistant Mycobacterium tuberculosis clinical isolates in southwestern China

The T120P or M172V mutation on rv2172c confers high level para-aminosalicylic acid resistance in Mycobacterium tuberculosis

Although para-aminosalicylic acid (PAS) has been used to treat tuberculosis for decades, mechanisms of resistance to this drug in Mycobacterium tuberculosis (M. tuberculosis) clinical isolates have not been thoroughly investigated. Previously, we found that decreased methylenetetrahydrofolate reductase (MTHFR) activity of Rv2172c led to increased sensitivity to antifolates in M. tuberculosis. In this study, we collected the genome-sequencing data of 173 PAS-resistant and 803 PAS-sensitive clinical isolates and analyzed rv2172c mutations in those 976 isolates. The results showed that two mutations (T120P and M172V) on rv2172c could be identified in a certain proportion (6.36%) of PAS-resistant isolates. The results of AlphaFold2 prediction indicated that the T120P or M172V mutation might affect the enzymatic activity of Rv2172c by influencing nicotinamide adenine dinucleotide (NADH) binding, and this was verified by subsequent biochemical analysis, demonstrating the role of residues Thr120 and Met172 on NADH binding and enzymatic activity of Rv2172c. In addition, the effect of rv2172c T120P or M172V mutation on methionine production and PAS resistance was determined in M. tuberculosis. The results showed that both T120P and M172V mutations caused increased intracellular methionine concentrations and high level PAS resistance. In summary, we discovered new molecular markers and also a novel mechanism of PAS resistance in M. tuberculosis clinical isolates and broadened the understanding of the NADH-dependent MTHFR catalytic mechanism of Rv2172c in M. tuberculosis, which will facilitate the molecular diagnosis of PAS resistance and also the development of new drugs targeting Rv2172c.

Breaking barriers: The potential of nanosystems in antituberculosis therapy

Tuberculosis (TB), caused by Mycobacterium tuberculosis, continues to pose a significant threat to global health. The resilience of TB is amplified by a myriad of physical, biological, and biopharmaceutical barriers that challenge conventional therapeutic approaches. This review navigates the intricate landscape of TB treatment, from the stealth of latent infections and the strength of granuloma formations to the daunting specters of drug resistance and altered gene expression. Amidst these challenges, traditional therapies often fail, contending with inconsistent bioavailability, prolonged treatment regimens, and socioeconomic burdens. Nanoscale Drug Delivery Systems (NDDSs) emerge as a promising beacon, ready to overcome these barriers, offering better drug targeting and improved patient adherence. Through a critical approach, we evaluate a spectrum of nanosystems and their efficacy against MTB both in vitro and in vivo. This review advocates for the intensification of research in NDDSs, heralding their potential to reshape the contours of global TB treatment strategies.

Mutations in the promoter region of methionine transporter gene metM (Rv3253c) confer para-aminosalicylic acid (PAS) resistance in Mycobacterium tuberculosis

Tuberculosis (TB) is a significant global public health threat. Despite the long-standing use of para-aminosalicylic acid (PAS) as a second-line anti-TB drug, its resistance mechanism remains unclear. In this study, we isolated 90 mutants of PAS-resistant Mycobacterium tuberculosis (MTB) H37Ra in 7H11 solid medium and performed whole-genome sequencing, gene overexpression, transcription level comparison and amino acid level determination in MTB, and promoter activity by β-galactosidase assays in Mycobacterium smegmatis to elucidate the mechanism of PAS resistance. Herein, we found that 47 of 90 (52.2%) PAS-resistant mutants had nine different mutations in the intergenic region of metM (Rv3253c) and Rv3254. Beta-galactosidase assays confirmed that mutations increased promoter activity only for metM but not Rv3254. Interestingly, overexpression of MetM or its M. smegmatis homolog (MSMEI_1796) either by its promoter in metM's direction or by exogenous expression in MTB induced PAS resistance in a methionine-dependent manner. Therefore, drug susceptibility results for the metM promoter mutants can be misleading when using standard 7H10 or 7H9 medium, which lacks methionine. At the metabolism level, PAS treatment led to higher intracellular methionine levels in the mutants than the wild type, antagonizing PAS and conferring resistance. Furthermore, 12 different mutations in the metM promoter were identified in clinical MTB strains. In summary, we found a novel mechanism of PAS resistance in MTB. Mutations in the metM (Rv3253c) promoter upregulate metM transcription and elevate intracellular methionine, which antagonize PAS. Our findings shed new light on the mechanism of PAS resistance in MTB and highlight issues with the current PAS susceptibility culture medium.IMPORTANCEAlthough para-aminosalicylic acid (PAS) has been used to treat TB for more than 70 years, the understanding of PAS resistance mechanisms is still vague, living gaps in our ability to predict resistance and apply PAS effectively in clinical practice. This study aimed to address this knowledge gap by inducing in vitro PAS resistance in Mycobacterium tuberculosis (MTB) using 7H11 medium and discovering a new PAS resistance mechanism. Our research revealed that spontaneous mutations occurring in the promoter region of the methionine transporting gene, metM, can upregulate the expression of metM, resulting in increased intracellular transport of methionine and consequently high-level resistance of Mycobacterium tuberculosis to PAS. Notably, this resistance phenotype cannot be observed when using the commonly recommended 7H10 medium, possibly due to the lack of additional methionine supply compared with that when using the 7H11 medium. Mutations on the regulatory region of metM were also found in some clinical MTB strains. These findings may have important implications for the unexplained PAS resistance observed in clinical settings and provide insight into the failures of PAS treatment. Additionally, they underscore the importance of considering the choice of culture media when conducting drug susceptibility testing for MTB.

Competition between H4PteGlu and H2PtePAS Confers para-Aminosalicylic Acid Resistance in Mycobacterium tuberculosis

Tuberculosis remains a serious challenge to human health worldwide. para-Aminosalicylic acid (PAS) is an important anti-tuberculosis drug, which requires sequential activation by Mycobacterium tuberculosis (M. tuberculosis) dihydropteroate synthase and dihydrofolate synthase (DHFS, FolC). Previous studies showed that loss of function mutations of a thymidylate synthase coding gene thyA caused PAS resistance in M. tuberculosis, but the mechanism is unclear. Here we showed that deleting thyA in M. tuberculosis resulted in increased content of tetrahydrofolate (H4PteGlu) in bacterial cells as they rely on the other thymidylate synthase ThyX to synthesize thymidylate, which produces H4PteGlu during the process. Subsequently, data of in vitro enzymatic activity experiments showed that H4PteGlu hinders PAS activation by competing with hydroxy dihydropteroate (H2PtePAS) for FolC catalysis. Meanwhile, over-expressing folC in ΔthyA strain and a PAS resistant clinical isolate with known thyA mutation partially restored PAS sensitivity, which relieved the competition between H4PteGlu and H2PtePAS. Thus, loss of function mutations in thyA led to increased H4PteGlu content in bacterial cells, which competed with H2PtePAS for catalysis by FolC and hence hindered the activation of PAS, leading to decreased production of hydroxyl dihydrofolate (H2PtePAS-Glu) and finally caused PAS resistance. On the other hand, functional deficiency of thyA in M. tuberculosis pushes the bacterium switch to an unidentified dihydrofolate reductase for H4PteGlu biosynthesis, which might also contribute to the PAS resistance phenotype. Our study revealed how thyA mutations confer PAS resistance in M. tuberculosis and provided new insights into studies on the folate metabolism of the bacterium.

Association between mutations in a thyX-hsdS.1 region and para-aminosalicylic acid resistance in Mycobacterium tuberculosis clinical isolates

Although para-aminosalicylic acid (PAS) has been used to treat tuberculosis agent for decades, its mechanisms of resistance are still not thoroughly understood. Previously, sporadic studies showed that certain mutations in the thyX-hsdS.1 region caused PAS resistance in M. tuberculosis, but a comprehensive analysis is lacking. Recently, we found a G-10A mutation in thyX-hsdS.1 in a PAS-resistant clinical isolate, but it did not cause PAS resistance. SNPs in thyX-hsdS.1 in 6550 clinical isolates were analyzed, and 153 SNPs were identified. C-16 T was the most common SNP identified (54.25%, 83/153), followed by C-4T (7.19%, 11/153) and G-9A (6.54%, 10/153). Subsequently, the effects of those SNPs on the promoter activity of thyX were tested, and the results showed that mutations C-1T, G-3A, C-4T, C-4G, G-7A, G-9A, C-16T, G-18C, and C-19G led to increased promoter activity compared with the wild-type sequence, but other mutations did not. Then, thyX and wild-type thyX-hsdS.1, or thyX-hsdS.1 containing specific SNPs, were overexpressed in M. tuberculosis H37Ra. The results showed that mutations resulting in increased promoter activity also caused PAS resistance. Moreover, the results of an electrophoretic mobility shift assay showed that thyX-hsdS.1 containing the C-16T mutation had a higher binding capacity to RNA polymerase than did the wild-type sequence. Taken together, our data demonstrated that among the SNPs identified in thyX-hsdS.1 of M. tuberculosis clinical isolates, only those able to increase the promoter activity of thyX caused PAS resistance and therefore can be considered as molecular markers for PAS resistance.

Gated Calcium Ion Channel and Mutation Mechanisms in Multidrug-Resistant Tuberculosis

A wide spectrum of Gram-positive/Gram-negative bacteria has been found resistant to a wide spectrum of antibiotics in the United States of America during the past decade. Drug-resistant tuberculosis is not yet a major threat in North/South America, Europe, and the Middle East. However, the migration of populations in times of drought, famine, and hostilities may increase the global reach of this ancient pathogen. Given an increased spread from China and India to African countries, drug-resistant Mycobacterium tuberculosis has become an emerging topic of concern for Europe and North America. Due to the dangers associated with the spread of pathogens among different populations, the World Health Organization continues to expand healthcare advisories for therapeutic approaches for both stationary and migrating populations. As much of the literature focuses on endemic to pandemic viruses, we remain concerned that other treatable communicable diseases may be ignored. One such disease is multidrug-resistant tuberculosis. We focus on molecular mechanisms that this pathogen relies upon for the development of multidrug resistance via gene mutation and the evolutionary development of new enzyme and calcium channels.

Determination of critical concentration for drug susceptibility testing of Mycobacterium tuberculosis against para-aminosalicylic acid with clinical isolates with thyA, folC and dfrA mutations

Background & Objectives

Accurate determination of antimicrobial resistance profiles is of great importance to formulate optimal regimens against multidrug-resistant tuberculosis (MDR-TB). Although para-aminosalicylic acid (PAS) has been widely used clinically, the reliable testing methods for PAS susceptibility were not established. Herein, we aimed to establish critical test concentration for PAS on the Mycobacterial Growth Indicator Tube (MGIT) 960 in our laboratory settings.

Methods

A total of 102 clinical isolates were included in this study, including 82 wild-type and 20 resistotype isolates. Minimum inhibitory concentration (MIC) was determined by MGIT 960. Whole-genome sequencing was used to identify the mutation patterns potentially conferring PAS resistance. Sequence alignment and structure modelling were carried out to analyze potential drug-resistant mechanism of folC mutant.

Results

Overall, the Minimum inhibitory concentration (MIC) distribution demonstrated excellent separation between wild-type and resistotype isolates. The wild-type population were all at least 1 dilution below 4 μg/ml, and the resistotype population were no lower than 4 μg/ml, indicating that 4 μg/ml was appropriate critical concentration to separate these two populations. Of 20 mutant isolates, 12 (60.0%) harbored thyA mutations, 2 (10%) had a mutation on upstream of dfrA, and the remaining isolates had folC mutations. Overall, thyA and folC mutations were scattered throughout the whole gene without any one mutation predominating. All mutations within thyA resulted in high-level resistance to PAS (MIC > 32 μg/ml); whereas the MICs of isolates with folC mutations exhibited great diversity, ranged from 4 to > 32 μg/ml, and sequence and structure analysis partially provided the possible reasons for this diversity.

Conclusions

We propose 4 μg/ml as tentative critical concentration for MGIT 960. The major mechanism of PAS resistance is mutations within thyA and folC in MTB isolations. The whole-gene deletion of thyA locus confers high-level resistance to PAS. The diversity of many distinct mutations scattered throughout the full-length folC gene challenges the PCR-based mutation analysis for PAS susceptibility.

Resistance and tolerance of Mycobacterium tuberculosis to antimicrobial agents-How M. tuberculosis can escape antibiotics

Tuberculosis (TB) poses a serious threat to public health worldwide since it was discovered. Until now, TB has been one of the top 10 causes of death from a single infectious disease globally. The treatment of active TB cases majorly relies on various anti-tuberculosis drugs. However, under the selection pressure by drugs, the continuous evolution of Mycobacterium tuberculosis (Mtb) facilitates the emergence of drug-resistant strains, further resulting in the accumulation of tubercle bacilli with multiple drug resistance, especially deadly multidrug-resistant TB and extensively drug-resistant TB. Researches on the mechanism of drug action and drug resistance of Mtb provide a new scheme for clinical management of TB patients, and prevention of drug resistance. In this review, we summarized the molecular mechanisms of drug resistance of existing anti-TB drugs to better understand the evolution of drug resistance of Mtb, which will provide more effective strategies against drug-resistant TB, and accelerate the achievement of the EndTB Strategy by 2035. This article is categorized under: Infectious Diseases > Molecular and Cellular Physiology.

Characterization of Fluoroquinolone-Resistant and Multidrug-Resistant Mycobacterium tuberculosis Isolates Using Whole-Genome Sequencing in Tianjin, China

Objective

Methods

Results

Conclusion

Decreased methylenetetrahydrofolate reductase activity leads to increased sensitivity to para-aminosalicylic acid in Mycobacterium tuberculosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is one of the most fatal diseases in the world. Methylenetetrahydrofolate reductase (MTHFR) catalyzes the production of 5-methyltetrahydrofolate (5-CH₃-THF), which is required for the de novo biosynthesis of methionine in bacteria. Here, we identified Rv2172c as an MTHFR in M. tuberculosis through in vitro and in vivo analyses and determined that the protein is essential for the in vitro growth of the bacterium. Subsequently, we constructed rv2172c R159N and L214A mutants in M. tuberculosis and found that these mutants were more sensitive to the antifolates para-aminosalicylic acid (PAS) and sulfamethoxazole (SMX). Combining biochemical and genetic methods, we found that rv2172c R159N or L214A mutation impaired methionine production, leading to increased susceptibility of M. tuberculosis to PAS, which was largely restored by adding exogenous methionine. Moreover, overexpression of rv2172c in M. tuberculosis could increase methionine production and lead to PAS resistance. This research is the first to identify an MTHFR in M. tuberculosis and reveals that the activity of this enzyme is associated with susceptibility to antifolates. These findings have particular value for antitubercular drug design for the treatment of drug-resistant TB.