Gene sequencing for routine verification of pyrazinamide resistance in Mycobacterium tuberculosis: a role for pncA but not rpsA

Mechanistic insights into the conformational changes and alterations in residual communications due to the mutations in the pncA Gene of Mycobacterium tuberculosis: A computational perspective for effective therapeutic solutions

Due to its emerging resistance to first-line anti-TB medications, tuberculosis (TB) is one of the most contagious illness in the world. According to reports, the effectiveness of treating TB is severely impacted by drug resistance, notably resistance caused by mutations in the pncA gene-encoded pyrazinamidase (PZase) to the front-line drug pyrazinamide (PZA). The present study focused on investigating the resistance mechanism caused by the mutations D12N, T47A, and H137R to better understand the structural and molecular events responsible for the resistance acquired by the pncA gene of Mycobacterium tuberculosis (MTB) at the structural level. Bioinformatics analysis predicted that all three mutations were deleterious and located near the active centre of the pncA, affecting its functional activity. Furthermore, molecular dynamics simulation (MDS) results established that mutations significantly reduced the structural stability and caused the rearrangement of FE2+ in the active centre of pncA. Moreover, essential dynamics analysis, including principal component analysis (PCA) and free energy landscape (FEL), concluded variations in the protein motion and decreased conformational space in the mutants. Additionally, the mutations potentially impacted the network topologies and altered the residual communications in the network. The complex simulation study results established the significant movement of the flap region from the active centre of mutant complexes, further supporting the flap region's significance in developing resistance to the PZA drug. This study advances our knowledge of the primary cause of the mechanism of PZA resistance and the structural dynamics of pncA mutants, which will help us to design new and potent chemical scaffolds to treat drug-resistant TB (DR-TB).

Genomic analysis of Mycobacterium tuberculosis variant bovis strains isolated from bovine in the state of Mato Grosso, Brazil

The species Mycobacterium tuberculosis variant bovis (M. tuberculosis var. bovis) is associated with tuberculosis, mainly in cattle and buffaloes. This pathogen has the potential to infect other mammals, including humans. Tuberculosis caused by M. tuberculosis var. bovis is a zoonosis clinically identical to tuberculosis caused by Mycobacterium tuberculosis, and the recommended treatment in humans results in the use of antibiotics. In this study, we used the whole genome sequencing (WGS) methodology Illumina NovaSeq 6000 System platform to characterize the genome of M. tuberculosis var. bovis in cattle circulating in Mato Grosso, identify mutations related to drug resistance genes, compare with other strains of M. tuberculosis var. bovis brazilian and assess potential drug resistance. Four isolates of M. tuberculosis var. bovis of cattle origin representing the main livestock circuits, which had been more prevalent in previous studies in the state of Mato Grosso, were selected for the genomic study. The genome sizes of the sequenced strains ranged from 4,306,423 to 4,332,964 bp, and the GC content was 65.6%. The four strains from Mato Grosso presented resistance genes to pncA (pyrazinamide), characterized as drug-resistant strains. In addition to verifying several point mutations in the pncA, rpsA, rpsL, gid, rpoB, katG, gyrB, gyrA, tlyA, embA, embB, embC, fgd, fbiB, and fbiC genes, these genes were similar to antibiotic resistance in more than 92% of the Brazilian strains. Therefore, our results indicated a high genetic diversity between our isolates and other M. tuberculosis var. bovis isolated in Brazil. Thus, multiple transmission routes of this pathogen may be present in the production chain. So, to achieve a bovine tuberculosis-free health status, the use of the WGS as a control and monitoring tool will be crucial to determine these transmission routes.

Structure activity relationship of pyrazinoic acid analogs as potential antimycobacterial agents

Tuberculosis (TB) remains a leading cause of infectious disease-related mortality and morbidity. Pyrazinamide (PZA) is a critical component of the first-line TB treatment regimen because of its sterilizing activity against non-replicating Mycobacterium tuberculosis (Mtb), but its mechanism of action has remained enigmatic. PZA is a prodrug converted by pyrazinamidase encoded by pncA within Mtb to the active moiety, pyrazinoic acid (POA) and PZA resistance is caused by loss-of-function mutations to pyrazinamidase. We have recently shown that POA induces targeted protein degradation of the enzyme PanD, a crucial component of the coenzyme A biosynthetic pathway essential in Mtb. Based on the newly identified mechanism of action of POA, along with the crystal structure of PanD bound to POA, we designed several POA analogs using structure for interpretation to improve potency and overcome PZA resistance. We prepared and tested ring and carboxylic acid bioisosteres as well as 3, 5, 6 substitutions on the ring to study the structure activity relationships of the POA scaffold. All the analogs were evaluated for their whole cell antimycobacterial activity, and a few representative molecules were evaluated for their binding affinity, towards PanD, through isothermal titration calorimetry. We report that analogs with ring and carboxylic acid bioisosteres did not significantly enhance the antimicrobial activity, whereas the alkylamino-group substitutions at the 3 and 5 position of POA were found to be up to 5 to 10-fold more potent than POA. Further development and mechanistic analysis of these analogs may lead to a next generation POA analog for treating TB.

Mutations Associated with Pyrazinamide Resistance in Mycobacterium tuberculosis: A Review and Update

Pyrazinamide (PZA) has remained a keystone of tuberculosis (TB) therapy, and it possesses high imperative sterilizing action that can facilitate reduction in the present chemotherapy regimen. The combination of PZA works both with first- and second-line TB drugs, notably fluoroquinolones, clofazimine, bedaquiline, delamanid and pretomanid. Pyrazinamide inhibits various targets that are involved in different cellular processes like energy production (pncA), trans-translation (rpsA) and pantothenate/coenzyme A (panD) which are required for persistence of the pathogen. It is well known that pncA gene encoding pyrazinamidase is involved in the transition of PZA into the active form of pyrazinoic acid, which implies that mutation in the pncA gene can develop PZA resistance in Mycobacterium tuberculosis (M. tuberculosis) strain leading to a major clinical and public health concern. Therefore, it is very crucial to understand its resistance mechanism and to detect it precisely to help in the management of the disease. Scope of this review is to have a deep understanding of molecular mechanism of PZA resistance with its multiple targets which would help study the association of mutations and its resistance in M. tuberculosis. This will in turn help learn about the resistance of PZA and develop more accurate molecular diagnostic tool for drug-resistant TB in future TB therapy.

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.

Diagnostic Accuracy of Pyrazinamide Susceptibility Testing in Mycobacterium tuberculosis: A Systematic Review with Meta-Analysis

Introduction: Pyrazinamide (PZA) susceptibility testing plays a critical role in determining the appropriate treatment regimens for multidrug-resistant tuberculosis. We conducted a systematic review and meta-analysis to evaluate the diagnostic accuracy of sequencing PZA susceptibility tests against culture-based susceptibility testing methods as the reference standard. Methods: We searched the MEDLINE/PubMed, Embase, and Web of Science databases for the relevant records. The QUADAS-2 tool was used to assess the quality of the studies. Diagnostic accuracy measures (i.e., sensitivity and specificity) were pooled with a random-effects model. All statistical analyses were performed with Meta-DiSc (version 1.4, Cochrane Colloquium, Barcelona, Spain), STATA (version 14, Stata Corporation, College Station, TX), and RevMan (version 5.3, The Nordic Cochrane Centre, the Cochrane Collaboration, Copenhagen, Denmark) software. Results: A total of 72 articles, published between 2000 and 2019, comprising data for 8,701 isolates of Mycobacterium tuberculosis were included in the final analysis. The pooled sensitivity and specificity of the PZA sequencing test against all reference tests (the combination of BACTEC mycobacteria growth indicator tube 960 (MGIT 960), BACTEC 460, and proportion method) were 87% (95% CI: 85-88) and 94.7% (95% CI: 94-95). The positive likelihood ratio, negative likelihood ratio, diagnostic odds ratio, and the area under the curve estimates were found to be 12.0 (95% CI: 9.0-16.0), 0.17 (95% CI: 0.13-0.21), 106 (95% CI: 71-158), and 96%, respectively. Deek's test result indicated a low likelihood for publication bias (p = 0.01). Conclusions: Our analysis indicated that PZA sequencing may be used in combination with conventional tests due to the advantage of the time to result and in scenarios where culture tests are not feasible. Further work to improve molecular tests would benefit from the availability of standardized reference standards and improvements to the methodology.

Structural and Genomic Insights Into Pyrazinamide Resistance in Mycobacterium tuberculosis Underlie Differences Between Ancient and Modern Lineages

Resistance to drugs used to treat tuberculosis disease (TB) continues to remain a public health burden, with missense point mutations in the underlying Mycobacterium tuberculosis bacteria described for nearly all anti-TB drugs. The post-genomics era along with advances in computational and structural biology provide opportunities to understand the interrelationships between the genetic basis and the structural consequences of M. tuberculosis mutations linked to drug resistance. Pyrazinamide (PZA) is a crucial first line antibiotic currently used in TB treatment regimens. The mutational promiscuity exhibited by the pncA gene (target for PZA) necessitates computational approaches to investigate the genetic and structural basis for PZA resistance development. We analysed 424 missense point mutations linked to PZA resistance derived from ∼35K M. tuberculosis clinical isolates sourced globally, which comprised the four main M. tuberculosis lineages (Lineage 1-4). Mutations were annotated to reflect their association with PZA resistance. Genomic measures (minor allele frequency and odds ratio), structural features (surface area, residue depth and hydrophobicity) and biophysical effects (change in stability and ligand affinity) of point mutations on pncA protein stability and ligand affinity were assessed. Missense point mutations within pncA were distributed throughout the gene, with the majority (>80%) of mutations with a destabilising effect on protomer stability and on ligand affinity. Active site residues involved in PZA binding were associated with multiple point mutations highlighting mutational diversity due to selection pressures at these functionally important sites. There were weak associations between genomic measures and biophysical effect of mutations. However, mutations associated with PZA resistance showed statistically significant differences between structural features (surface area and residue depth), but not hydrophobicity score for mutational sites. Most interestingly M. tuberculosis lineage 1 (ancient lineage) exhibited a distinct protein stability profile for mutations associated with PZA resistance, compared to modern lineages.

Overcoming the Challenges of Pyrazinamide Susceptibility Testing in Clinical Mycobacterium tuberculosis Isolates

Pyrazinamide (PZA) is one of the first-line agents used for the treatment of tuberculosis. However, current phenotypic PZA susceptibility testing in the Bactec MGIT 960 system is unreliable, and false resistance is well documented. Rapid identification of resistance-associated mutations can confirm the phenotypic result. This study aimed to investigate the use of genotypic methods in combination with phenotypic susceptibility testing for confirmation of PZA-resistant Mycobacterium tuberculosis isolates. Sanger sequencing and/or whole-genome sequencing were performed to detect mutations in pncA, rpsA, panD, and clpC1. Isolates were screened for heteroresistance, and PZA susceptibility testing was performed using the Bactec MGIT 960 system using a reduced inoculum to investigate false resistance. Overall, 40 phenotypically PZA-resistant isolates were identified. Of these, PZA resistance was confirmed in 22/40 (55%) isolates by detecting mutations in the pncA, rpsA, and panD genes. Of the 40 isolates, 16 (40%) were found to be susceptible using the reduced inoculum method (i.e., false resistance). No mutations were detected in two PZA-resistant isolates. False resistance was observed in isolates with MICs close to the critical concentration. In particular, East African Indian strains (lineage 1) appeared to have an elevated MIC that is close to the critical concentration. While this study illustrates the complexity and challenges associated with PZA susceptibility testing of M. tuberculosis, we conclude that a combination of genotypic and phenotypic drug susceptibility testing methods is required for accurate detection of PZA resistance.

Characterization of rifampicin-resistant Mycobacterium tuberculosis in Khyber Pakhtunkhwa, Pakistan

Tuberculosis (TB), caused by Mycobacterium tuberculosis, is endemic in Pakistan. Resistance to both firstline rifampicin and isoniazid drugs (multidrug-resistant TB; MDR-TB) is hampering disease control. Rifampicin resistance is attributed to rpoB gene mutations, but rpoA and rpoC loci may also be involved. To characterise underlying rifampicin resistance mutations in the TB endemic province of Khyber Pakhtunkhwa, we sequenced 51 M. tuberculosis isolates collected between 2016 and 2019; predominantly, MDR-TB (n = 44; 86.3%) and lineage 3 (n = 30, 58.8%) strains. We found that known mutations in rpoB (e.g. S405L), katG (e.g. S315T), or inhA promoter loci explain the MDR-TB. There were 24 unique mutations in rpoA, rpoB, and rpoC genes, including four previously unreported. Five instances of within-host resistance diversity were observed, where two were a mixture of MDR-TB strains containing mutations in rpoB, katG, and the inhA promoter region, as well as compensatory mutations in rpoC. Heteroresistance was observed in two isolates with a single lineage. Such complexity may reflect the high transmission nature of the Khyber Pakhtunkhwa setting. Our study reinforces the need to apply sequencing approaches to capture the full-extent of MDR-TB genetic diversity, to understand transmission, and to inform TB control activities in the highly endemic setting of Pakistan.

Profiling and identification of novel rpoB mutations in rifampicin-resistant Mycobacterium tuberculosis clinical isolates from Pakistan

INTRODUCTION

Rifampicin (RIF) is one of the most effective anti-tuberculosis first-line drugs prescribed along with isoniazid. However, the emergence of RIF resistance Mycobacterium tuberculosis (MTB) isolates is a major issue towards tuberculosis (TB) control program in high MDR TB-burdened countries including Pakistan. Molecular data behind phenotypic resistance is essential for better management of RIF resistance which has been linked with mutations in rpoB gene. Since molecular studies on RIF resistance is limited in Pakistan, the current study was aimed to investigate the molecular data of mutations in rpoB gene behind phenotypic RIF resistance isolates in Pakistan.

METHOD

A total of 322 phenotypically RIF-resistant isolates were randomly selected from National TB Reference Laboratory, Pakistan for sequencing while 380 RIF resistance whole-genome sequencing (WGS) of Pakistani isolates (BioProject PRJEB25972), were also analyzed for rpoB mutations.

RESULT

Among the 702 RIF resistance samples, 675 (96.1%) isolates harbored mutations in rpoB in which 663 (94.4%) were detected within the Rifampicin Resistance Determining Region (RRDR) also known as a mutation hot spot region, including three novel. Among these mutations, 657 (97.3%) were substitutions including 603 (89.3%) single nucleotide polymorphism, 49 (7.25%) double and five (0.8%) triple. About 94.4% of Phenotypic RIF resistance strains, exhibited mutations in RRDR, which were also detectable by GeneXpert.

CONCLUSION

Mutations in the RRDR region of rpoB is a major mechanism of RIF resistance in MTB circulating isolates in Pakistan. Molecular detection of drug resistance is a faster and better approach than phenotypic drug susceptibility testing to reduce the time for transmission of RIF resistance strains in population. Such insights will inform the deployment of anti-TB drug regimens and disease control tools and strategies in high burden settings, such as Pakistan.

Evaluating the Frequency of Resistance to Pyrazinamide Among Drug-resistant Strains of Mycobacterium tuberculosis in Isfahan, Iran

Background: Pyrazinamide is one of the most important first-line medications for the treatment of tuberculosis and an alternative intake for MDR-TB and XDR-TB patients. Objectives: The purpose of this study was to evaluate resistance to pyrazinamide in the isolates resistant to the Mycobacterium tuberculosis drug in patients in the city of Isfahan. Methods: In this study, the drug susceptibility test was performed with pyrazinamide using the proportion method and PZA assay on 47 isolates resistant to Mycobacterium tuberculosis. Then, the mutations of the pncA and rpsA genes of the isolates resistant to pyrazinamide were evaluated by the sequencing method. Results: According to the proportion method, 19 cases were resistant to pyrazinamide, 16 of which had mutations in their pncA and rpsA genes. Besides, five new mutations were recorded, and three isolates lacked mutations in the mentioned genes. Conclusions: Pyrazinamide resistance is high in MDR-TB and INH mono-resistant isolates. Therefore, evaluating the susceptibility to pyrazinamide in patients with MDR-TB before the initiation of treatment with pyrazinamide is considered essential.

Development of New Therapeutics to Meet the Current Challenge of Drug Resistant Tuberculosis

Tuberculosis (TB) is a prominent infective disease and a major reason of mortality/ morbidity globally. Mycobacterium tuberculosis causes a long-lasting latent infection in a significant proportion of human population. The increasing burden of tuberculosis is mainly caused due to multi drug-resistance. The failure of conventional treatment has been observed in large number of cases. Drugs that are used to treat extensively drug-resistant tuberculosis are expensive, have limited efficacy, and have more side effects for a longer duration of time and are often associated with poor prognosis. To regulate the emergence of multidrug resistant tuberculosis, extensively drug-resistant tuberculosis and totally drug resistant tuberculosis, efforts are being made to understand the genetic/molecular basis of target drug delivery and mechanisms of drug resistance. Understanding the molecular approaches and pathology of Mycobacterium tuberculosis through whole genome sequencing may further help in the improvement of new therapeutics to meet the current challenge of global health. Understanding cellular mechanisms that trigger resistance to Mycobacterium tuberculosis infection may expose immune associates of protection, which could be an important way for vaccine development, diagnostics, and novel host-directed therapeutic strategies. The recent development of new drugs and combinational therapies for drug-resistant tuberculosis through major collaboration between industry, donors, and academia gives an improved hope to overcome the challenges in tuberculosis treatment. In this review article, an attempt was made to highlight the new developments of drug resistance to the conventional drugs and the recent progress in the development of new therapeutics for the treatment of drugresistant and non-resistant cases.

Computational screening of potential glioma-related genes and drugs based on analysis of GEO dataset and text mining

BACKGROUND

Considering the high invasiveness and mortality of glioma as well as the unclear key genes and signaling pathways involved in the development of gliomas, there is a strong need to find potential gene biomarkers and available drugs.

METHODS

Eight glioma samples and twelve control samples were analyzed on the GSE31095 datasets, and differentially expressed genes (DEGs) were obtained via the R software. The related glioma genes were further acquired from the text mining. Additionally, Venny program was used to screen out the common genes of the two gene sets and DAVID analysis was used to conduct the corresponding gene ontology analysis and cell signal pathway enrichment. We also constructed the protein interaction network of common genes through STRING, and selected the important modules for further drug-gene analysis. The existing antitumor drugs that targeted these module genes were screened to explore their efficacy in glioma treatment.

RESULTS

The gene set obtained from text mining was intersected with the previously obtained DEGs, and 128 common genes were obtained. Through the functional enrichment analysis of the identified 128 DEGs, a hub gene module containing 25 genes was obtained. Combined with the functional terms in GSE109857 dataset, some overlap of the enriched function terms are both in GSE31095 and GSE109857. Finally, 4 antitumor drugs were identified through drug-gene interaction analysis.

CONCLUSIONS

In this study, we identified that two potential genes and their corresponding four antitumor agents could be used as targets and drugs for glioma exploration.

Drug resistance gene mutations and treatment outcomes in MDR-TB: A prospective study in Eastern China

Background

Multidrug-resistant tuberculosis (MDR-TB) poses a serious challenge to TB control. It is of great value to search for drug resistance mutation sites and explore the roles that they play in the diagnosis and prognosis of MDR-TB.

Methods

We consecutively enrolled MDR-TB patients from five cities in Jiangsu Province, China, between January 2013 and December 2014. Drug susceptibility tests of rifampin, isoniazid, ofloxacin, and kanamycin were routinely performed by proportion methods on Lowenstein–Jensen (LJ) medium. Drug resistance-related genes were sequenced, and the consistency of genetic mutations and phenotypic resistance was compared. The association between mutations and treatment outcomes was expressed as odds ratios (ORs) and 95% confidence intervals (CIs).

Results

Among 87 MDR-TB patients, 71 with treatment outcomes were involved in the analysis. The proportion of successful treatment was 50.7% (36/71). The rpoB gene exhibited the highest mutation rate (93.0%) followed by katG (70.4%), pncA (33.8%), gyrA (29.6%), eis (15.5%), rrs (12.7%), gyrB (9.9%) and rpsA (4.2%). Multivariable analysis demonstrated that patients with pncA gene mutations (adjusted OR: 19.69; 95% CI: 2.43–159.33), advanced age (adjusted OR: 13.53; 95% CI: 1.46–124.95), and nonstandard treatment (adjusted OR: 7.72; 95% CI: 1.35–44.35) had a significantly higher risk of poor treatment outcomes.

Conclusions

These results suggest that Mycobacterium tuberculosis gene mutations may be related to phenotypic drug susceptibility. The pncA gene mutation along with treatment regimen and age are associated with the treatment outcomes of MDR-TB.

Multidrug-resistant tuberculosis (MDR-TB) exacerbates the already serious tuberculosis epidemic, poses a notable threat to global tuberculosis control, and places a considerable burden on developing countries, as treatments for MDR-TB tend to be expensive, of limited efficacy, and toxic. Genotypic determinants of resistance to specific drugs or drug classes offer a rapid and highly specific alternative to phenotypic drug susceptibility testing. Although the relationship between gene mutations and drug resistance has been described previously, the strength of the association of mutations with the treatment outcomes of MDR tuberculosis have not been fully elucidated. The results of our study, which was conducted in a Chinese population, suggest that gene mutations in Mycobacterium tuberculosis may be related to phenotypic drug susceptibility. Mutation of the pncA gene contributes to a poor prognosis and can be applied to predict the treatment outcomes of MDR-TB.

Pyrazinamide Resistance and Mutation Patterns Among Multidrug-Resistant Mycobacterium tuberculosis from Henan Province

PURPOSE

This study was designed to identify the phenotypic and genotypic characteristics of pyrazinamide (PZA) resistance among multidrug-resistant Mycobacterium tuberculosis (MDR-TB) from Henan and to evaluate the efficacy of pncA, rpsA, and panD mutations in predicting PZA resistance.

MATERIALS AND METHODS

A total of 152 MDR strains were included in this study. The Bactec MGIT system was used to determine PZA susceptibility for all strains. The pncA, rpsA, and panD genes were sequenced to identify any mutations, and the sequences were then aligned with the sequence of standard strain H37Rv. Moreover, the correlations between PZA-resistant phenotypes and treatment outcomes were analysed.

RESULTS

Of the152 strains, 105 had a PZA-resistant phenotype, and 102 harboured the pncA mutation. The PZA resistance rate was higher in the strains with resistance to all four first-line drugs and those that were pre-extensively drug-resistant (pre-XDR) and extensively drug-resistant (XDR). A total of 100 different pncA mutation patterns were identified, including 80 point mutations and 20 insertions/deletions, and 32 new pncA mutation patterns were detected. In this study, 13 strains had multiple mutations. Of the11 PZA-resistant strains without pncA mutations, two harboured the rpsA mutation, and one harboured the panD mutation. With PZA susceptibility results as the reference, single-gene pncA sequencing had sensitivity of 89.52% and specificity of 89.36%. With the combination of rpsA and panD, the sensitivity increased to 92.38%, and the specificity remained the same. No significant differences were observed in the sputum smear/culture conversion rate between PZA-resistant patients and PZA-sensitive patients. However, PZA resistance was related to the time to sputum smear/culture conversion (P = 0.018).

CONCLUSION

The combination of pncA, rpsA, and panD was beneficial for the timely diagnosis of PZA resistance and could provide a laboratory basis for customizing treatment regimens for MDR-TB patients.

Mycobacterium tuberculosis ribosomal protein S1 (RpsA) and variants with truncated C-terminal end show absence of interaction with pyrazinoic acid

Pyrazinamide (PZA) is an antibiotic used in first- and second-line tuberculosis treatment regimens. Approximately 50% of multidrug-resistant tuberculosis and over 90% of extensively drug-resistant tuberculosis strains are also PZA resistant. Despite the key role played by PZA, its mechanisms of action are not yet fully understood. It has been postulated that pyrazinoic acid (POA), the hydrolyzed product of PZA, could inhibit trans-translation by binding to Ribosomal protein S1 (RpsA) and competing with tmRNA, the natural cofactor of RpsA. Subsequent data, however, indicate that these early findings resulted from experimental artifact. Hence, in this study we assess the capacity of POA to compete with tmRNA for RpsA. We evaluated RpsA wild type (WT), RpsA ∆A438, and RpsA ∆A438 variants with truncations towards the carboxy terminal end. Interactions were measured using Nuclear Magnetic Resonance spectroscopy (NMR), Isothermal Titration Calorimetry (ITC), Microscale Thermophoresis (MST), and Electrophoretic Mobility Shift Assay (EMSA). We found no measurable binding between POA and RpsA (WT or variants). This suggests that RpsA may not be involved in the mechanism of action of PZA in Mycobacterium tuberculosis, as previously thought. Interactions observed between tmRNA and RpsA WT, RpsA ∆A438, and each of the truncated variants of RpsA ∆A438, are reported.

The Bewildering Antitubercular Action of Pyrazinamide

Pyrazinamide (PZA) is a cornerstone antimicrobial drug used exclusively for the treatment of tuberculosis (TB). Due to its ability to shorten drug therapy by 3 months and reduce disease relapse rates, PZA is considered an irreplaceable component of standard first-line short-course therapy for drug-susceptible TB and second-line treatment regimens for multidrug-resistant TB. Despite over 60 years of research on PZA and its crucial role in current and future TB treatment regimens, the mode of action of this unique drug remains unclear. Defining the mode of action for PZA will open new avenues for rational design of novel therapeutic approaches for the treatment of TB. In this review, we discuss the four prevailing models for PZA action, recent developments in modulation of PZA susceptibility and resistance, and outlooks for future research and drug development.

Value of pyrazinamide for composition of new treatment regimens for multidrug-resistant Mycobacterium tuberculosis in China

Background

Pyrazinamide still may be a useful drug for treatment of rifampin-resistant (RR-TB) or multidrug-resistant tuberculosis (MDR-TB) in China while awaiting scale up of new drugs and regimens including bedaquiline and linezolid. The level of pyrazinamide resistance among MDR-TB patients in China is not well established. Therefore, we assessed pyrazinamide resistance in a representative sample and explored determinants and patterns of pncA mutations.

Methods

MDR-TB isolates from the 2007 national drug resistance survey of China were sub-cultured and examined for pyrazinamide susceptibility by BACTEC MGIT 960 method. pncA mutations were identified by sequencing. Characteristics associated with pyrazinamide resistance were analyzed using univariable and multivariable log-binominal regression.

Results

Of 401 MDR-TB isolates, 324 were successfully sub-cultured and underwent drug susceptibility testing. Pyrazinamide resistance was prevalent in 40.7% of samples, similarly among new and previously treated MDR-TB patients. Pyrazinamide resistance in MDR-TB patients was associated with lower age (adjusted OR 0.54; 95% CI, 0.34–0.87 for those aged ≧60 years compared to < 40 years). Pyrazinamide resistance was not associated with gender, residential area, previous treatment history and Beijing genotype. Of 132 patients with pyrazinamide resistant MDR-TB, 97 (73.5%) had a mutation in the pncA gene; with 61 different point mutations causing amino acid change, and 11 frameshifts in the pncA gene. The mutations were scattered throughout the whole pncA gene and no hot spot region was identified.

Conclusions

Pyrazinamide resistance among MDR-TB patients in China is common, although less so in elderly patients. Therefore, pyrazinamide should only be used for treatment of RR/MDR-TB in China if susceptibility is confirmed. Molecular testing for detection of pyrazinamide resistance only based on pncA mutations has certain value for the rapid detection of pyrazinamide resistance in MDR-TB strains but other gene mutations conferring to pyrazinamide resistance still need to be explored to increase its predictive ability .

Pharmacological and Molecular Mechanisms Behind the Sterilizing Activity of Pyrazinamide

Inclusion of pyrazinamide (PZA) in the tuberculosis (TB) drug regimen during the 1970s enabled a reduction in treatment duration from 12 to 6 months. PZA has this remarkable effect in patients despite displaying poor potency against Mycobacterium tuberculosis (Mtb) in vitro. The pharmacological basis for the in vivo sterilizing activity of the drug has remained obscure and its bacterial target controversial. Recently it was shown that PZA penetrates necrotic caseous TB lung lesions and kills nongrowing, drug-tolerant bacilli. Furthermore, it was uncovered that PZA inhibits bacterial Coenzyme A biosynthesis. It may block this pathway by triggering degradation of its target, aspartate decarboxylase. The elucidation of the pharmacological and molecular mechanisms of PZA provides the basis for the rational discovery of the next-generation PZA with improved in vitro potency while maintaining attractive pharmacological properties.

Pyrazinoic Acid Inhibits the Bifunctional Enzyme (Rv2783) in Mycobacterium tuberculosis by Competing with tmRNA

Pyrazinamide (PZA) is a key drug for tuberculosis treatment. The active form of PZA, pyrazinoic acid (POA), appears to inhibit multiple targets in M. tuberculosis. Recently, the bifunctional enzyme Rv2783 was reported as a new target of POA. However, the mechanism by which POA inhibits Rv2783 is not yet clear. Here, we report how a new A2104C substitution in Rv2783c, identified in PZA-resistant clinical isolates, conferred resistance to PZA in M. tuberculosis. Expression of the mutant allele recapitulated the PZA resistance. All catalytic activities of Rv2783, but not the mutant, were inhibited by POA. Additionally, POA competed with transfer-messenger RNA (tmRNA) for binding to Rv2783, other than the mutant. These results provide new insight into the molecular mechanism of the antitubercular activity of PZA.

Resistance To First-Line Antituberculosis Drugs And Prevalence Of pncA Mutations In Clinical Isolates Of Mycobacterium tuberculosis From Zunyi, Guizhou Province Of China

Background

China is one of the high-burden countries for multidrug-resistant tuberculosis (MDR-TB), and pyrazinamide is one of the anti-TB drugs used for the shorter MDR-TB treatment regimen. The aim of this study was to determine the correlation between pncA gene mutations and resistance to four first-line anti-TB drugs as well as treatment history in clinical isolates of Mycobacterium tuberculosis.

Patients and methods

M. tuberculosis clinical isolates were collected from 318 in-patients with smear-positive TB between October 2008 and September 2016 at a major hospital in Zunyi, Guizhou Province of China, and used for drug susceptibility testing against four first-line anti-TB drugs. Genomic DNA extracted from clinical isolates was used for PCR amplification and DNA sequencing of the pncA gene.

Results

Among 318 clinical isolates, 129 (40.6%), 170 (53.5%), 66 (20.8%) and 109 (34.3%) were resistant to rifampicin, isoniazid, ethambutol and streptomycin respectively. In addition, 124 clinical isolates were MDR-TB and 71.8% of them were previously treated cases. Sequencing results showed that 46.8% of MDR-TB and 2.2% of drug susceptible isolates harbored a pncA mutation, and 52 types of pncA mutations were detected from 64 isolates. The prevalence of pncA mutations in isolates resistant to first-line anti-TB drugs and previously treated TB cases was significantly higher than that in drug-susceptible isolates and new cases of TB.

Conclusion

High prevalence of pncA mutations in clinical isolates of M. tuberculosis from Zunyi, Guizhou Province of China, is correlated with resistance to four first-line anti-TB drugs, MDR-TB and previously treated TB cases.

Marine Natural Products and Drug Resistance in Latent Tuberculosis

Pyrazinamide (PZA) is the only drug for the elimination of latent Mycobacterium tuberculosis (MTB) isolates. However, due to the increased number of PZA-resistance, the chances of the success of global TB elimination seems to be more prolonged. Recently, marine natural products (MNPs) as an anti-TB agent have received much attention, where some compounds extracted from marine sponge, Haliclona sp. exhibited strong activity under aerobic and hypoxic conditions. In this study, we screened articles from 1994 to 2019 related to marine natural products (MNPs) active against latent MTB isolates. The literature was also mined for the major regulators to map them in the form of a pathway under the dormant stage. Five compounds were found to be more suitable that may be applied as an alternative to PZA for the better management of resistance under latent stage. However, the mechanism of actions behind these compounds is largely unknown. Here, we also applied synthetic biology to analyze the major regulatory pathway under latent TB that might be used for the screening of selective inhibitors among marine natural products (MNPs). We identified key regulators of MTB under latent TB through extensive literature mining and mapped them in the form of regulatory pathway, where SigH is negatively regulated by RshA. PknB, RshA, SigH, and RNA polymerase (RNA-pol) are the major regulators involved in MTB survival under latent stage. Further studies are needed to screen MNPs active against the main regulators of dormant MTB isolates. To reduce the PZA resistance burden, understanding the regulatory pathways may help in selective targets of MNPs from marine natural sources.

Drug-resistance in Mycobacterium tuberculosis: where we stand

Tuberculosis (TB), an infectious disease caused by the bacterium Mycobacterium tuberculosis (Mtb), has burdened vulnerable populations in modern day societies for decades. Recently, this global health threat has been heightened by the emergence and propagation of multi drug-resistant (MDR) and extensively drug-resistant (XDR) strains of Mtb that are resistant to current treatment regimens. The End-TB strategy, launched by the World Health Organization (WHO), aims to reduce TB-related deaths by 90%. This program encourages universal access to drug susceptibility testing, which is not widely available owing to the lack of laboratory capacity or resources in certain under-resourced areas. Clinical assays are further complicated by the slow growth of Mtb, resulting in the long turn-around time of tests which severely limits their application in guiding a patient's treatment regimen. This review provides a comprehensive overview of current TB treatments, mechanisms of resistance to anti-tubercular drugs and their diagnosis and the current pipeline of drugs targeting drug-resistant TB (DR-TB) with particular attention paid to ways in which drug-resistance is combated.

Direct Detection of Pyrazinamide Resistance in Mycobacterium tuberculosis by Use of pncA PCR Sequencing

An in-house-developed pncA sequencing assay for analysis of pyrazinamide (PZA) resistance was evaluated using 162 archived Mycobacterium tuberculosis complex (MTBC) isolates with phenotypic PZA susceptibility profiles that were well defined by analysis of Bactec MGIT 960 PZA kit and PZase activity data. Preliminary results showed 100% concordance between pncA sequencing and phenotypic PZA drug susceptibility test (DST) results among archived isolates. Also, 637 respiratory specimens were prospectively collected, and 158 were reported as MTBC positive by the Abbott Realtime MTB assay (96.3% sensitivity [95% confidence interval {CI}: 92.2% to 98.7%]; 100% specificity [95% CI: 99.2% to 100.0%]). Genotypic and phenotypic PZA resistance profiles of these 158 MTBC-positive specimens were analyzed by pncA sequencing and Bactec MGIT 960 PZA kit, respectively. For analysis of PZA resistance, pncA sequencing detected pncA mutations in 5/5 (100%) phenotypic PZA-resistant respiratory specimens within 4 working days. No pncA mutations were detected among PZA-susceptible specimens. Combining archived isolates with prospective specimens, 27 were identified as phenotypic PZA resistant with pncA mutation. Among these 27 samples, 6/27 (22.2%) phenotypic PZA-resistant strains carried novel pncA mutations without rpsA and panD mutations. These included 5 with mutations (a deletion [Del] at 383T [Del383T], Del 380 to 390, insertion of A [A Ins] at position 127, A Ins at position 407, and G Ins at position 508) in pncA structural genes and 1 with a mutation (T-12C) at the pncA promoter region. All six of these strains had no or reduced PZase activities, indicating that the novel mutations might confer PZA resistance. Additionally, 25/27 phenotypic PZA-resistant strains were confirmed multidrug-resistant tuberculosis (MDR-TB) strains. As PZA is commonly used in MDR-TB treatment regimens, direct pncA sequencing will rapidly detect PZA resistance and facilitate judicious use of PZA in treating PZA-susceptible MDR-TB.

Introducing RpsA Point Mutations Δ438A and D123A into the Chromosome of Mycobacterium tuberculosis Confirms Their Role in Causing Resistance to Pyrazinamide

Pyrazinamide (PZA) is a unique frontline drug for shortening tuberculosis (TB) treatment, but its mechanisms of action are elusive. We previously found one PZA-resistant strain that harbors an alanine deletion at position 438 (Δ438A) in RpsA, a target of PZA associated with PZA resistance, but its role in causing PZA resistance has been inconclusive. Here, we introduced the RpsA Δ438A mutation along with the D123A mutation into the Mycobacterium tuberculosis chromosome and demonstrated that these RspA mutations are indeed responsible for PZA resistance.

Revised Interpretation of the Hain Lifescience GenoType MTBC To Differentiate Mycobacterium canettii and Members of the Mycobacterium tuberculosis Complex

Using 894 phylogenetically diverse genomes of the Mycobacterium tuberculosis complex (MTBC), we simulated in silico the ability of the Hain Lifescience GenoType MTBC assay to differentiate the causative agents of tuberculosis. Here, we propose a revised interpretation of this assay to reflect its strengths (e.g., it can distinguish some strains of Mycobacterium canettii and variants of Mycobacterium bovis that are not intrinsically resistant to pyrazinamide) and limitations (e.g., Mycobacterium orygis cannot be differentiated from Mycobacterium africanum).

Pyrazinamide resistance and mutations in pncA among isolates of Mycobacterium tuberculosis from Khyber Pakhtunkhwa, Pakistan

Background

Pyrazinamide (PZA) is an important component of first-line drugs because of its distinctive capability to kill subpopulations of persistent Mycobacterium tuberculosis (MTB). The prodrug (PZA) is converted to its active form, pyrazinoic acid (POA) by MTB pncA-encoded pyrazinamidase (PZase). Mutation in pncA is the most common and primary cause of PZA resistance. The aim of the present study was to explore the molecular characterization of PZA resistance in a Pashtun-dominated region of Khyber Pakhtunkhwa, Pakistan.

Methods

We performed drug susceptibility testing (DST) on 753 culture-positive isolates collected from the Provincial Tuberculosis Control Program Khyber Pakhtunkhwa using the BACTEC MGIT 960 PZA method. In addition, the pncA gene was sequenced in PZA-resistant isolates, and PZA susceptibility testing results were used to determine the sensitivity and specificity of pncA gene mutations.

Results

A total of 69 isolates were PZA resistant (14.8%). Mutations were investigated in 69 resistant, 26 susceptible and one H37Rv isolates by sequencing. Thirty-six different mutations were identified in PZA-resistant isolates, with fifteen mutations, including 194_203delCCTCGTCGTG and 317_318delTC, that have not been reported in TBDRM and GMTV Databases and previous studies. Mutations Lys96Thr and Ser179Gly were found in the maximum number of isolates (n = 4 each). We did not detect mutations in sensitive isolates, except for the synonymous mutation 195C > T (Ser65Ser). The sensitivity and specificity of the pncA sequencing method were 79.31% (95% CI, 69.29 to 87.25%) and 86.67% (95% CI, 69.28 to 96.24%).

Conclusion

Mutations in the pncA gene in circulating isolates of geographically distinct regions, especially in high-burden countries, should be investigated for better control and management of drug-resistant TB. Molecular methods for the investigation of PZA resistance are better than DST.

Genetics and roadblocks of drug resistant tuberculosis

Considering the extensive evolutionary history of Mycobacterium tuberculosis, anti-Tuberculosis (TB) drug therapy exerts a recent selective pressure. However, in a microorganism devoid of horizontal gene transfer and with a strictly clonal populational structure such as M. tuberculosis the usual, but not sole, path to overcome drug susceptibility is through de novo mutations on a relatively strict set of genes. The possible allelic diversity that can be associated with drug resistance through several mechanisms such as target alteration or target overexpression, will dictate how these genes can become associated with drug resistance. The success demonstrated by this pathogenic microbe in this latter process and its ability to spread is currently one of the major obstacles to an effective TB elimination. This article reviews the action mechanism of the more important anti-TB drugs, including bedaquiline and delamanid, along with new findings on specific resistance mechanisms. With the development, validation and endorsement of new in vitro molecular tests for drug resistance, knowledge on these resistance mechanisms and microevolutionary dynamics leading to the emergence and fixation of drug resistance mutations within the host is highly important. Additionally, the fitness toll imposed by resistance development is also herein discussed together with known compensatory mechanisms. By elucidating the possible mechanisms that enable one strain to reacquire the original fitness levels, it will be theoretically possible to make more informed decisions and develop novel strategies that can force M. tuberculosis microevolutionary trajectory down through a path of decreasing fitness levels.

Lead compounds and key residues of ribosomal protein S1 in drug-resistant Mycobacterium tuberculosis

Ribosomal protein S1 (RpsA) has been identified as a novel target of pyrazinoic acid (POA), which is the active form of pyrazinamide (PZA), in vivo. RpsA plays a crucial role in trans-translation, which is widespread in microbes. In our investigation, we first described the discovery of promising RpsA antagonists for drug-resistant mycobacterium (MtRpsAd438A) and M. smegmatis, as well as wild-type M. tuberculosis. These antagonists were discovered via structure/ligand-based virtual screening approaches. A total of 21 targeted compounds were selected by virtual screening, combined scores, affinity, similarities and rules for potential as drugs. Next, the affinities of these compounds for three targeted proteins were tested in vitro by applying various technologies, including fluorescence quenching titration (FQT), saturation transfer difference (STD), and chemical shift perturbation (CSP) assays. The results showed that seven compounds had a high affinity for the targeted proteins. Our discovery set the stage for discovering new chemical entities (NCEs) for PZA-resistant tuberculosis and providing key residues for rational drug design to target RpsA.

Characterization of pncA mutations in multi-drug and pyrazinamide resistant Mycobacterium tuberculosis isolates cultured from Queensland migrants and Papua New Guinea residents

Outbreak of drug resistant tuberculosis in the Western province, Papua New Guinea is a concern to Queensland, Australia due to migration. We performed pncA mutation analysis and genotyping of multi-drug/pyrazinamide (MDR/PZA) resistant isolates from 18 Queensland (Qld) migrants and 81 Papua New Guinea (PNG) residents, to compare with phenotypic evidence of PZA resistance and to evaluate the genotypes obtained from the two countries. Seven different mutations were seen from Qld isolates of which 2 have not been described previously. A cluster of mutations were found between amino acids L35 and S65. Amongst the PNG isolates, 10 mutations were identified, of which 6 were unique and have not been described previously. Majority of the mutations formed 2 clusters, between amino acids Q10 to A20 and W68 to W119. Mutations identified at nucleotide (nt) position 202 and 307 were found to be the most common types, occurring in 25% and 51% of the PNG isolates respectively. The majority of the mutations were seen in MDR/PZA resistant isolates. These mutations could be utilized for direct screening of PZA resistance from PNG patient samples. Genotypic analysis of the isolates showed strong clustering amongst the PNG isolates as opposed to Qld isolates. A diversity of mutations and genotypes were seen amongst the Qld migrant isolates. Majority of PNG isolates had one genotype with two distinct pncA mutation patterns (T202C and T307G) which highlight on-going transmission. pncA mutation analysis provided a satisfactory alternative to PZA culture DST with high positive predictive value and an improved result turnaround time.

Evolution of drug resistance in Mycobacterium tuberculosis: a review on the molecular determinants of resistance and implications for personalized care

Drug-resistant TB (DR-TB) remains a significant challenge in TB treatment and control programmes worldwide. Advances in sequencing technology have significantly increased our understanding of the mechanisms of resistance to anti-TB drugs. This review provides an update on advances in our understanding of drug resistance mechanisms to new, existing drugs and repurposed agents. Recent advances in WGS technology hold promise as a tool for rapid diagnosis and clinical management of TB. Although the standard approach to WGS of Mycobacterium tuberculosis is slow due to the requirement for organism culture, recent attempts to sequence directly from clinical specimens have improved the potential to diagnose and detect resistance within days. The introduction of new databases may be helpful, such as the Relational Sequencing TB Data Platform, which contains a collection of whole-genome sequences highlighting key drug resistance mutations and clinical outcomes. Taken together, these advances will help devise better molecular diagnostics for more effective DR-TB management enabling personalized treatment, and will facilitate the development of new drugs aimed at improving outcomes of patients with this disease.

Molecular Targets Related Drug Resistance Mechanisms in MDR-, XDR-, and TDR-Mycobacterium tuberculosis Strains

Tuberculosis (TB) is a formidable infectious disease that remains a major cause of death worldwide today. Escalating application of genomic techniques has expedited the identification of increasing number of mutations associated with drug resistance in Mycobacterium tuberculosis. Unfortunately the prevalence of bacillary resistance becomes alarming in many parts of the world, with the daunting scenarios of multidrug-resistant tuberculosis (MDR-TB), extensively drug-resistant tuberculosis (XDR-TB) and total drug-resistant tuberculosis (TDR-TB), due to number of resistance pathways, alongside some apparently obscure ones. Recent advances in the understanding of the molecular/ genetic basis of drug targets and drug resistance mechanisms have been steadily made. Intriguing findings through whole genome sequencing and other molecular approaches facilitate the further understanding of biology and pathology of M. tuberculosis for the development of new therapeutics to meet the immense challenge of global health.

Practice Guidelines for Clinical Microbiology Laboratories: Mycobacteria

Mycobacteria are the causative organisms for diseases such as tuberculosis (TB), leprosy, Buruli ulcer, and pulmonary nontuberculous mycobacterial disease, to name the most important ones. In 2015, globally, almost 10 million people developed TB, and almost half a million patients suffered from its multidrug-resistant form. In 2016, a total of 9,287 new TB cases were reported in the United States. In 2015, there were 174,608 new case of leprosy worldwide. India, Brazil, and Indonesia reported the most leprosy cases. In 2015, the World Health Organization reported 2,037 new cases of Buruli ulcer, with most cases being reported in Africa. Pulmonary nontuberculous mycobacterial disease is an emerging public health challenge. The U.S. National Institutes of Health reported an increase from 20 to 47 cases/100,000 persons (or 8.2% per year) of pulmonary nontuberculous mycobacterial disease among adults aged 65 years or older throughout the United States, with 181,037 national annual cases estimated in 2014. This review describes contemporary methods for the laboratory diagnosis of mycobacterial diseases. Furthermore, the review considers the ever-changing health care delivery system and stresses the laboratory's need to adjust and embrace molecular technologies to provide shorter turnaround times and a higher quality of care for the patients who we serve.

Phenotypic and genotypic characterization of pyrazinamide resistance among multidrug-resistant Mycobacterium tuberculosis clinical isolates in Hangzhou, China

OBJECTIVES

Pyrazinamide (PZA) is a crucial first-line tuberculosis (TB) drug recommended for both drug-susceptible and multidrug-resistant Mycobacterium tuberculosis. This study aimed to evaluate the performance of the sequencing method of pncA, rpsA and panD mutations in detecting PZA resistance in multidrug-resistant (MDR) TB isolates.

METHODS

We sequenced the pncA, rpsA and panD genes and performed PZA susceptibility tests across 291 MDR-TB isolates to evaluate the performance of the sequencing method of these genes in detecting PZA resistance.

RESULTS

Results showed that 145 (90.0%) of 161 PZA phenotypic resistant isolates had mutations in pncA. Among the 16 isolates (10.0%) which did not have mutations in pncA, ten and three isolates had mutations in rpsA and panD, respectively. The sequencing method for detecting mutations in pncA alone had 90.1% (95% confidence interval (CI), 84.4-94.2) sensitivity and 92.3% (95% CI, 86.3-96.3) specificity. The combination of all three genes increased the sensitivity from 90.1% (95% CI, 84.4-94.2) to 98.1% (95% CI, 94.7-99.6) (p < 0.001) while the specificity remained unchanged. In 120 PZA-susceptible and 16 PZA-resistant isolates without pncA mutations, rpsA/panD mutations were correlated with PZA resistance.

CONCLUSIONS

PZA resistance was largely associated with mutations in pncA. Mutations in rpsA and panD were also associated with PZA resistance in MDR isolates expressing wild-type pncA. The detection of mutations in pncA, rpsA and panD can be useful for the determination of PZA resistance.

Pyrazinoic Acid Inhibits Mycobacterial Coenzyme A Biosynthesis by Binding to Aspartate Decarboxylase PanD

Previously, we showed that a major in vitro and in vivo mechanism of resistance to pyrazinoic acid (POA), the bioactive component of the critical tuberculosis (TB) prodrug pyrazinamide (PZA), involves missense mutations in the aspartate decarboxylase PanD, an enzyme required for coenzyme A biosynthesis. What is the mechanism of action of POA? Upon demonstrating that treatment of M. bovis BCG with POA resulted in a depletion of intracellular coenzyme A and confirming that this POA-mediated depletion is prevented by either missense mutations in PanD or exogenous supplementation of pantothenate, we hypothesized that POA binds to PanD and that this binding blocks the biosynthetic pathway. Here, we confirm both hypotheses. First, metabolomic analyses showed that POA treatment resulted in a reduction of the concentrations of all coenzyme A precursors downstream of the PanD-mediated catalytic step. Second, using isothermal titration calorimetry, we established that POA, but not its prodrug PZA, binds to PanD. Binding was abolished for mutant PanD proteins. Taken together, these findings support a mechanism of action of POA in which the bioactive component of PZA inhibits coenzyme A biosynthesis via binding to aspartate decarboxylase PanD. Together with previous works, these results establish PanD as a genetically, metabolically, and biophysically validated target of PZA.

A multiple genome analysis of Mycobacterium tuberculosis reveals specific novel genes and mutations associated with pyrazinamide resistance

BACKGROUND

Tuberculosis (TB) is a major global health problem and drug resistance compromises the efforts to control this disease. Pyrazinamide (PZA) is an important drug used in both first and second line treatment regimes. However, its complete mechanism of action and resistance remains unclear.

RESULTS

We genotyped and sequenced the complete genomes of 68 M. tuberculosis strains isolated from unrelated TB patients in Peru. No clustering pattern of the strains was verified based on spoligotyping. We analyzed the association between PZA resistance with non-synonymous mutations and specific genes. We found mutations in pncA and novel genes significantly associated with PZA resistance in strains without pncA mutations. These included genes related to transportation of metal ions, pH regulation and immune system evasion.

CONCLUSIONS

These results suggest potential alternate mechanisms of PZA resistance that have not been found in other populations, supporting that the antibacterial activity of PZA may hit multiple targets.

A comprehensive characterization of PncA polymorphisms that confer resistance to pyrazinamide

Tuberculosis chemotherapy is dependent on the use of the antibiotic pyrazinamide, which is being threatened by emerging drug resistance. Resistance is mediated through mutations in the bacterial gene pncA. Methods for testing pyrazinamide susceptibility are difficult and rarely performed, and this means that the full spectrum of pncA alleles that confer clinical resistance to pyrazinamide is unknown. Here, we performed in vitro saturating mutagenesis of pncA to generate a comprehensive library of PncA polymorphisms resultant from a single-nucleotide polymorphism. We then screened it for pyrazinamide resistance both in vitro and in an infected animal model. We identify over 300 resistance-conferring substitutions. Strikingly, these mutations map throughout the PncA structure and result in either loss of enzymatic activity and/or decrease in protein abundance. Our comprehensive mutational and screening approach should stand as a paradigm for determining resistance mutations and their mechanisms of action.The antibiotic pyrazinamide is central to tuberculosis treatment regimens, globally. Despite its efficacy, resistance to the drug is increasing. Here, Eric Rubin and colleagues characterise the genetic basis of pyrazinamide resistance.

A Multinational Analysis of Mutations and Heterogeneity in PZase, RpsA, and PanD Associated with Pyrazinamide Resistance in M/XDR Mycobacterium tuberculosis

Pyrazinamide (PZA) is an important first-line drug in all existing and new tuberculosis (TB) treatment regimens. PZA-resistance in M. tuberculosis is increasing, especially among M/XDR cases. Noted issues with PZA Drug Susceptibility Testing (DST) have driven the search for alternative tests. This study provides a comprehensive assessment of PZA molecular diagnostics in M/XDR TB cases. A set of 296, mostly XDR, clinical M. tuberculosis isolates from four countries were subjected to DST for eight drugs, confirmatory Wayne's assay, and whole-genome sequencing. Three genes implicated in PZA resistance, pncA, rpsA, and panD were investigated. Assuming all non-synonymous mutations cause resistance, we report 90% sensitivity and 65% specificity for a pncA-based molecular test. The addition of rpsA and panD potentially provides 2% increase in sensitivity. Molecular heterogeneity in pncA was associated with resistance and should be evaluated as a diagnostic tool. Mutations near the N-terminus and C-terminus of PZase were associated with East-Asian and Euro-American lineages, respectively. Finally, Euro-American isolates are most likely to have a wild-type PZase and escape molecular detection. Overall, the 8-10% resistance without markers may point to alternative mechanisms of resistance. Confirmatory mutagenesis may improve the disconcertingly low specificity but reduce sensitivity since not all mutations may cause resistance.

A brief primer on genomic epidemiology: lessons learned from Mycobacterium tuberculosis

Genomics is now firmly established as a technique for the investigation and reconstruction of communicable disease outbreaks, with many genomic epidemiology studies focusing on revealing transmission routes of Mycobacterium tuberculosis. In this primer, we introduce the basic techniques underlying transmission inference from genomic data, using illustrative examples from M. tuberculosis and other pathogens routinely sequenced by public health agencies. We describe the laboratory and epidemiological scenarios under which genomics may or may not be used, provide an introduction to sequencing technologies and bioinformatics approaches to identifying transmission-informative variation and resistance-associated mutations, and discuss how variation must be considered in the light of available clinical and epidemiological information to infer transmission.

Drug resistance mechanisms and novel drug targets for tuberculosis therapy

Drug-resistant tuberculosis (TB) poses a significant challenge to the successful treatment and control of TB worldwide. Resistance to anti-TB drugs has existed since the beginning of the chemotherapy era. New insights into the resistant mechanisms of anti-TB drugs have been provided. Better understanding of drug resistance mechanisms helps in the development of new tools for the rapid diagnosis of drug-resistant TB. There is also a pressing need in the development of new drugs with novel targets to improve the current treatment of TB and to prevent the emergence of drug resistance in Mycobacterium tuberculosis. This review summarizes the anti-TB drug resistance mechanisms, furnishes some possible novel drug targets in the development of new agents for TB therapy and discusses the usefulness using known targets to develop new anti-TB drugs. Whole genome sequencing is currently an advanced technology to uncover drug resistance mechanisms in M. tuberculosis. However, further research is required to unravel the significance of some newly discovered gene mutations in their contribution to drug resistance.

Pyrazinamide Resistance Is Caused by Two Distinct Mechanisms: Prevention of Coenzyme A Depletion and Loss of Virulence Factor Synthesis

Pyrazinamide (PZA) is a critical component of first- and second-line treatments of tuberculosis (TB), yet its mechanism of action largely remains an enigma. We carried out a genetic screen to isolate Mycobacterium bovis BCG mutants resistant to pyrazinoic acid (POA), the bioactive derivative of PZA, followed by whole genome sequencing of 26 POA resistant strains. Rather than finding mutations in the proposed candidate targets fatty acid synthase I and ribosomal protein S1, we found resistance conferring mutations in two pathways: missense mutations in aspartate decarboxylase panD, involved in the synthesis of the essential acyl carrier coenzyme A (CoA), and frameshift mutations in the vitro nonessential polyketide synthase genes mas and ppsA-E, involved in the synthesis of the virulence factor phthiocerol dimycocerosate (PDIM). Probing for cross resistance to two structural analogs of POA, nicotinic acid and benzoic acid, showed that the analogs share the PDIM- but not the CoA-related mechanism of action with POA. We demonstrated that POA depletes CoA in wild-type bacteria, which is prevented by mutations in panD. Sequencing 10 POA-resistant Mycobacterium tuberculosis H37Rv isolates confirmed the presence of at least 2 distinct mechanisms of resistance to the drug. The emergence of resistance through the loss of a virulence factor in vitro may explain the lack of clear molecular patterns in PZA-resistant clinical isolates, other than mutations in the prodrug-converting enzyme. The apparent interference of POA with virulence pathways may contribute to the drug's excellent in vivo efficacy compared to its modest in vitro potency.

Prevalence of pyrazinamide resistance across the spectrum of drug resistant phenotypes of Mycobacterium tuberculosis

Pyrazinamide resistance is largely unknown in the spectrum of drug resistant phenotypes. We summarize data on PZA resistance in clinical isolates from South Africa. PZA DST should be performed when considering its inclusion in treatment of patients with rifampicin-resistant TB or MDR-TB.

Antibiotic resistance mechanisms in M. tuberculosis: an update

Treatment of tuberculosis (TB) has been a therapeutic challenge because of not only the naturally high resistance level of Mycobacterium tuberculosis to antibiotics but also the newly acquired mutations that confer further resistance. Currently standardized regimens require patients to daily ingest up to four drugs under direct observation of a healthcare worker for a period of 6-9 months. Although they are quite effective in treating drug susceptible TB, these lengthy treatments often lead to patient non-adherence, which catalyzes for the emergence of M. tuberculosis strains that are increasingly resistant to the few available anti-TB drugs. The rapid evolution of M. tuberculosis, from mono-drug-resistant to multiple drug-resistant, extensively drug-resistant and most recently totally drug-resistant strains, is threatening to make TB once again an untreatable disease if new therapeutic options do not soon become available. Here, I discuss the molecular mechanisms by which M. tuberculosis confers its profound resistance to antibiotics. This knowledge may help in developing novel strategies for weakening drug resistance, thus enhancing the potency of available antibiotics against both drug susceptible and resistant M. tuberculosis strains.

A quantitative adaptation of the Wayne test for pyrazinamide resistance

BACKGROUND

Pyrazinamide (PZA) is the most important drug against the latent stage of tuberculosis (TB) and is used in both first and second line treatment regimens. The continued increase in multi-drug resistant TB and the prevalence of PZA resistance makes the development of alternative assays for prompt identification of PZA resistance all the more important.

METHODS

We standardized and evaluated a quantitative variant of the Wayne assay (QW) for determining PZA resistance in Mycobacterium tuberculosis strains. This assay quantifies M. tuberculosis metabolism of PZA and production of pyrazinoic acid (POA) using visible spectrophotometry. We evaluated this method using PZA concentrations of 400 μg/ml and 800 μg/ml at incubation periods of 3, 5 and 7 days. M. tuberculosis strains from 68 sputum samples were also tested with the standard Wayne assay, Tetrazolium Microplate Assay (TEMA), Bactec 460TB and pncA sequencing. We compared QW and standard Wayne assay against a dichotomous reference classification using concordant Bactec 460TB and pncA sequencing. Secondarily, we determined the quantitative correlation between both QW values and TEMA's minimum inhibitory concentration (MIC) against Bactec 460TB percentage growth.

RESULTS

The standard Wayne showed sensitivity of 88% and specificity of 97.5%, giving a Youden Index (YI) of 0.855 against reference tests. The QW showed maximum YI of 0.934 on day 7 at 400 μg/ml PZA with 96% sensitivity and 97.4% specificity. Absorbance OD values for 400 μg/ml PZA were more accurate than 800 μg/ml PZA. Although QW showed high accuracy for PZA susceptibility, it did not correlate quantitatively with Bactec percentage growth. TEMA testing was unreliable and did not correlate with Bactec results.

CONCLUSIONS

The proposed QW assay is an inexpensive method capable of providing standardization and automation of colorimetric PZA resistance testing, with better discriminatory than the standard Wayne assay.

Pyrazinamide resistance in Mycobacterium tuberculosis: Review and update

The global control and management of tuberculosis (TB) is faced with the formidable challenge of worsening scenarios of drug-resistant disease. Pyrazinamide (PZA) is an indispensable first-line drug used for the treatment of TB. It plays a key role in reducing TB relapse rates, shortening the course of the disease treatment from 9-12 months to 6 months, and the treatment of patients infected with bacillary strains that are resistant to at least isoniazid and rifampicin. Additionally, it is the only first-line anti-TB drug most likely to be maintained in all new regimens, which are aimed at reducing the treatment period of susceptible, multi-drug resistant and extensively drug-resistant TB. It has a preferential sterilizing activity against non-replicating persister bacilli with low metabolism at acid pH in vitro or in vivo during active inflammation where other drugs may not act so well. PZA seem to have a non-specific cellular target and instead, exerts its anti-mycobacterial effect by disrupting the membrane energetics, the trans-translation process, acidification of the cytoplasm and perhaps coenzyme A synthesis, which is required for survival of Mycobacterium tuberculosis (MTB) persisters. Indeed, the emergence of MTB strains resistant to PZA represents an important clinical and public health problem. The essential role of PZA in TB treatment underlines the need for accurate and rapid detection of its resistance. This article presents an updated review of the molecular mechanisms of drug action and resistance in MTB against PZA, commenting on the several research gaps and proposed drug targets for PZA.

Molecular Basis of Drug Resistance in Mycobacterium tuberculosis

In this chapter we review the molecular mechanisms of drug resistance to the major first- and second-line antibiotics used to treat tuberculosis.

Pyrazinamide resistance among multidrug-resistant tuberculosis clinical isolates in a national referral center of China and its correlations with pncA, rpsA, and panD gene mutations

Our study was aimed to identify the phenotypic and genotypic pyrazinamide (PZA) resistance features among multidrug-resistant (MDR) isolates in a national tuberculosis (TB) referral center of China. PZA susceptibility test was performed for a total of 142 MDR-TB clinical isolates using the MGIT 960 PZA kits, and the pncA, rpsA, and panD genes were sequenced. Extensively drug-resistant (XDR) and pre-XDR strains had higher PZA resistance rate than that of MDR strains which were still sensitive to fluoroquinolone and aminoglycoside (42.9%, 24/56) (χ(2)=8.922, P=0.012). No panD mutation was detected among the PZA resistant strains with wild-type pncA and rpsA genes. Our study indicates that PZA-resistant frequency increases with TB drug resistance level; pncA, rpsA, and panD mutations had strong, low, and no correlation with PZA resistance, and rapid molecular assay will facilitate the timely identification of the PZA-sensitive MDR-TB.