Mutations in rpoB and katG genes of multidrug resistant mycobacterium tuberculosis undetectable using genotyping diagnostic methods

New insight in molecular detection of Mycobacterium tuberculosis

Mycobacterium tuberculosis, the causative agent of tuberculosis, is a pathogenic bacterium that has claimed millions of lives since the Middle Ages. According to the World Health Organization's report, tuberculosis ranks among the ten deadliest diseases worldwide. The presence of an extensive array of genes and diverse proteins within the cellular structure of this bacterium has provided us with a potent tool for diagnosis. While the culture method remains the gold standard for tuberculosis diagnosis, it is possible that molecular diagnostic methods, emphasis on the identification of mutation genes (e.g., rpoB and gyrA) and single nucleotide polymorphisms, could offer a safe and reliable alternative. Over the past few decades, as our understanding of molecular genetics has expanded, methods have been developed based on gene expansion and detection. These methods typically commence with DNA amplification through nucleic acid targeted techniques such as polymerase chain reaction. Various molecular compounds and diverse approaches have been employed in molecular assays. In this review, we endeavor to provide an overview of molecular assays for the diagnosis of tuberculosis with their properties (utilization, challenges, and functions). The ultimate goal is to explore the potential of replacing traditional bacterial methods with these advanced molecular diagnostic techniques.

Mutations and insights into the molecular mechanisms of resistance of Mycobacterium tuberculosis to first-line

Genetically antimicrobial resistance in Mycobacterium tuberculosis is currently one of the most important aspects of tuberculosis, considering that there are emerging resistant strains for almost every known drug used for its treatment. There are multiple antimicrobials used for tuberculosis treatment, and the most effective ones are the first-line drugs, which include isoniazid, pyrazinamide, rifampicin, and ethambutol. In this context, understanding the mechanisms of action and resistance of these molecules is essential for proposing new therapies and strategies of treatment. Additionally, understanding how and where mutations arise conferring a resistance profile to the bacteria and their effect on bacterial metabolism is an important requisite to be taken in producing safer and less susceptible drugs to the emergence of resistance. In this review, we summarize the most recent literature regarding novel mutations reported between 2017 and 2022 and the advances in the molecular mechanisms of action and resistance against first-line drugs used in tuberculosis treatment, highlighting recent findings in pyrazinamide resistance involving PanD and, additionally, resistance-conferring mutations for novel drugs such as bedaquiline, pretomanid, delamanid and linezolid.

Drug Resistance and Molecular Characteristics of Mycobacterium tuberculosis: A Single Center Experience

In recent years, the incidence of tuberculosis (TB) and mortality caused by the disease have been decreasing. However, the number of drug-resistant tuberculosis patients is increasing rapidly year by year. Here, a total of 380 Mycobacterium tuberculosis (MTB)-positive formalin-fixed and paraffin-embedded tissue (FFPE) specimens diagnosed in the Department of Pathology of the Eighth Medical Center, Chinese PLA General Hospital were collected. Among 380 cases of MTB, 85 (22.37%) were susceptible to four anti-TB drugs and the remaining 295 (77.63%) were resistant to one or more drugs. The rate of MDR-TB was higher in previously treated cases (52.53%) than in new cases [(36.65%), p  <  0.05]. Of previously treated cases, the rate of drug resistance was higher in females than in males (p  <  0.05). Among specimens obtained from males, the rate of drug resistance was higher in new cases than in previously treated cases (p  <  0.05). Of mutation in drug resistance-related genes, the majority (53/380, 13.95%) of rpoB gene carried the D516V mutation, and 13.42% (51/380) featured mutations in both the katG and inhA genes. Among the total specimens, 18.68% (71/380) carried the 88 M mutation in the rpsL gene, and the embB gene focused on the 306 M2 mutation with a mutation rate of 19.74%. Among the resistant INH, the mutation rate of −15 M was higher in resistance to more than one drug than in monodrug-resistant (p  <  0.05). In conclusion, the drug resistance of MTB is still very severe and the timely detection of drug resistance is conducive to the precise treatment of TB.

Frequency of rpoB, katG, and inhA Gene Polymorphisms Associated with Multidrug-Resistant Mycobacterium tuberculosis Complex Isolates among Ethiopian TB Patients: A Systematic Review

Tuberculosis (TB) is one of the top 10 causes of mortality and the first killer among infectious diseases of poverty (IDoPs) worldwide. It disproportionately affects on-third of the world's low-income countries including Ethiopia. One of the factors driving the TB epidemic is the global rise of MDR/XDR-TB and their low detection affect the global TB control progress. Recently, the resistance-associated genetic mutations in MTBC known to confer drug resistance have been detected by rapid molecular diagnostic tests and sequencing methods. In this article, the published literature searched by PubMed database from 2010 to 2021 and English language were considered. The aim of this systematic review was to assess the prevalence of the most common rpoB, katG, and inhA gene mutations associated with multidrug resistance in MTBC clinical strains among TB patients in Ethiopia. Though 22 studies met our eligibility criteria, only 6 studies were included in the final analysis. Using the molecular GenoType MTBDRplus and MTBDRsl line probe assay and sequencing procedures, a total of 932 culture-positive MTBC isolates were examined to determine RIF, INH, and MDR-TB resistance patterns along with rpoB, katG, and inhA gene mutation analysis. As a result, among the genotypically tested MTBC isolates, 119 (12.77%), 83 (8.91%), and 73 (7.32%) isolates were INH, RIF, and MDR-TB resistant, respectively. In any RIF-resistant MTBC strains, the most common single point mutations were in codon 531 (S531L) followed by codon 526 (H526Y) of the rpoB gene. Besides, the most common mutations in any INH-resistant MTBC were strains observed at codon 315 (S315T) and WT probe in the katG gene and at codon C15T and WT1 probe in the inhA promoter region. Detection of resistance allele in rpoB, KatG, and inhA genes for RIF and INH could serve as a marker for MDR-TB strains. Tracking the most common S531L, S315T, and C15T mutations in rpoB, katG, and inhA genes among RIF- and INH-resistant isolates would be valuable in TB diagnostics and treatment regimens, and could reduce the development and risk of MDR/XDR-TB drug-resistance patterns.

Genotypic and phenotypic drug-resistance detection and prevalence of heteroresistance in patients with isoniazid- and multidrug-resistant tuberculosis in Ethiopia

Objective

To assess the agreement between genotypic and phenotypic methods for detecting drug resistance, and examine the prevalence of heteroresistance among isoniazid (INH)- and multidrug/rifampicin-resistant (MDR/RR) TB.

Method

In total, 127 Mycobacterium tuberculosis (Mtb) isolates, including 65 MDR/RR and 62 INH resistant, were used. First-line drug susceptibility testing (DST) was performed using the LJ method to determine the percentage of resistant bacteria. All drug-resistant isolates underwent testing with LPA. Heteroresistance was defined as simultaneous detection of wild-type and resistance-conferring mutations using LPA.

Result

The sensitivity of LPA (compared with LJ DST) was 96% for any INH-resistant TB and 94% for any RR TB. The prevalence of heteroresistance among the 123. Mtb isolates was 9.8%. The percentage of resistant bacteria ranged from 1% to 10% for heteroresistant TB. Rifampicin heteroresistance was detected in 1.6% of MDR TB patients. INH heteroresistance was detected in 1.6% and 16.7% of MDR and INH-resistant TB patients, respectively. The proportion of INH heteroresistance was significantly higher (p = 0.030) in persons living with HIV.

Conclusion

Some phenotypic drug resistances were not captured by LPA. The prevalence and percentage of resistant bacteria among heteroresistant TB highlight the importance of LPA for early detection of heteroresistant TB.

Prevalence of drug resistance-conferring mutations associated with isoniazid- and rifampicin-resistant Mycobacterium tuberculosis in Ethiopia: a systematic review and meta-analysis

OBJECTIVES

Globally, the incidence and mortality of tuberculosis (TB) are declining; however, low detection of drug-resistant disease threatens to reverse current progress toward global TB control. Multiple rapid molecular diagnostic tests have recently been developed to detect genetic mutations in Mycobacterium tuberculosis (Mtb) known to confer drug resistance. However, their utility depends on the frequency and distribution of resistance-associated mutations in the pathogen population. This review aimed to assess the prevalence of gene mutations associated with rifampicin (RIF)- and isoniazid (INH)-resistant Mtb in Ethiopia.

METHODS

We searched the literature in PubMed/MEDLINE, Web of Science, Scopus and Cochrane Library. Data analysis was conducted in Stata 11.

RESULTS

Totally, 909 (95.8%) of 949 INH-resistant Mtb isolates had detectable gene mutations: 95.8% in katG315 and 5.9% in the inhA promoter region. Meta-analysis resulted in an estimated pooled prevalence of katGMUT1(S315T1) of 89.2% (95% CI 81.94-96.43%) and a pooled prevalence of inhAMUT1(C15T) of 77.5% (95% CI 57.84-97.13%). Moreover, 769 (90.8%) of 847 RIF-resistant strains had detectable rpoB gene mutations. Meta-analysis resulted in a pooled prevalence of rpoBMUT3(S531L) of 74.2% (95% CI 66.39-82.00%).

CONCLUSION

RIF-resistant Mtb were widespread, particularly those harbouring rpoB(S531L) mutation. Similarly, INH-resistant Mtb with katG(S315T1) and inhA(C15T) mutations were common. Tracking S531L, S315T1 and C15T mutations among RIF- and INH-resistant isolates, respectively, would be diagnostically and epidemiologically valuable. Rapid diagnosis of RIF- and INH-resistant Mtb would expedite modification of TB treatment regimens, and proper timely infection control interventions could reduce the risk of development and transmission of multidrug-resistant TB.

Mycobacterium tuberculosis SIT42 Infection in an Abused Dog in Southern Italy

A case of Mycobacterium tuberculosis infection is described in a dead adult male dog in Southern Italy. The carcass was found by the Health Authority in a gypsy encampment. It was admitted to our forensic veterinary medicine unit, with a suspicion of cruelty to the animal. Necropsy showed beating and traumatism signs, and mistreating was confirmed. Gross lesions included multiple nodular hepatic lesions, hemorrhagic enteritis with enlarged mesenteric lymph nodes, body cavity effusions, and an adrenal neoplasm. Bacteriological and molecular analyses were carried out on the liver lesions that enabled to identify M. tuberculosis SIT42 (LAM9). Drug-resistance patterns were evaluated by screening mutations on the rpoB and katG genes that showed susceptibility to both rifampin and isoniazid, respectively. Very few studies report canine tuberculosis, and little is known about the disease in Italy. To the authors' knowledge, this is the first report of Mycobacterium tuberculosis SIT42 infection in a dog in Italy.

In Silico Analysis of S315T and S315R Mutations of Multidrug-resistant Mycobacterium tuberculosis Clinical Isolates from Karachi, Pakistan

Background: Tuberculosis is one of the most frequent and persistent global diseases causing millions of deaths every year. Pakistan lies at number 6 among the 22 most dominant countries, with multidrug resistance up to 15%. Isoniazid-resistant strains of Mycobacterium tuberculosis are gradually rising and seem to be more prevalent in developing countries. Mutations in the katG gene are considered to be responsible for the accusation of isoniazid resistance in M. tuberculosis. Objectives: The current study was designed to investigate the structural and functional associations of KatG gene mutations (S315R and S315T) and multidrug resistance in M. tuberculosis isolates from Karachi, Pakistan. Results: The present study revealed conformational changes in the structure of the KatG enzyme due to observed mutations, which led to induced alterations in isoniazid binding residues at the active site of the KatG enzyme. Furthermore, substantial changes were observed in interaction energy, ligand-receptor energy, electrostatic energy, salvation energy, and ligand-receptor conformational entropy. All these resultant modifications due to S315R and S315T mutations ultimately reduced the flexibility and stability of proteins at isoniazid-binding residues. Conclusions: This deviation in the consistency of protein texture eventually compromises the enzyme activity. It is well expected that the outcomes of the current study would provide a better understanding of the consequences of these mutations and provide a detailed insight into some previously unknown features.

Differential DNA methylomes of clinical MDR, XDR and XXDR Mycobacterium tuberculosis isolates revealed by using single-molecule real-time sequencing

Post-replicative DNA methylation is essential for diverse biological processes in both eukaryotes and prokaryotes. Mycobacterium tuberculosis (M. tuberculosis), the causative agent of tuberculosis, remains one of the most formidable threats worldwide. Although DNA methylation of M. tuberculosis has been documented, little information is available for clinical drug-resistant M. tuberculosis. Single-molecule real-time (SMRT) sequencing was used to profile the core methylome of three clinical isolates, namely multidrug-resistant (MDR), extensively drug-resistant (XDR) and extremely drug-resistant (XXDR) strains. 3812, 6808 and 6041 DNA methylated sites were identified in MDR-MTB, XDR-MTB and XXDR-MTB genome, respectively. There are two types of methylated motifs, namely N⁶-methyladenine (m6A) and N⁴-methylcytosine (m4C). A novel widespread 6 mA methylation motif 5'-CACGCAG-3' was found in XDR-MTB and XXDR-MTB. The methylated genes are involved in multiple cellular processes, especially metabolic enzymes engaged in glucose metabolism, fatty acid and TCA cycle. Many methylated genes are involved in mycobacterial virulence, antibiotic resistance and tolerance. This provided a comprehensive list of methylated genes in drug-resistant clinical isolates and the basis for further functional elucidation.

Mutations in Mycobacterium tuberculosis Isolates with Discordant Results for Drug-Susceptibility Testing in Peru

Evaluation of resistance to antituberculosis drugs is routinely performed with genotypic or phenotypic methods; however, discordance can be seen between these different methodologies. Our objective was to identify mutations that could explain discordant results in the evaluation of susceptibility to rifampicin and isoniazid between molecular and phenotypic methods, using whole genome sequencing (WGS). Peruvian strains showing sensitive results in the GenoType MTBDRplus v2.0 test and resistant results in the proportions in the agar-plaque test for isoniazid or rifampin were selected. Discordance was confirmed by repeating both tests, and WGS was performed, using the Next Generation Sequencing methodology. Obtained sequences were aligned “through reference” (genomic mapping) using the program BWA with the algorithm “mem”, using as a reference the genome of the M. tuberculosis H37Rv strain. Discordance was confirmed in 14 strains for rifampicin and 21 for isoniazid, with 1 strain in common for both antibiotics, for a total of 34 unique strains. The most frequent mutation in the rpoB gene in the discordant strains for rifampicin was V170F. The most frequent mutations in the discordant strains for isoniazid were katG R463L, kasA G269S, and Rv1592c I322V. Several other mutations are reported. This is the first study in Latin America addressing mutations present in strains with discordant results between genotypic and phenotypic methods to rifampicin and isoniazid. These mutations could be considered as future potential targets for genotypic tests for evaluation of susceptibility to these drugs.

Structural Basis for Inhibition of Enoyl-[Acyl Carrier Protein] Reductase (InhA) from Mycobacterium tuberculosis

Background::

The enzyme trans-enoyl-[acyl carrier protein] reductase (InhA) is a central protein for the development of antitubercular drugs. This enzyme is the target for the pro-drug isoniazid, which is catalyzed by the enzyme catalase-peroxidase (KatG) to become active.

Objective::

Our goal here is to review the studies on InhA, starting with general aspects and focusing on the recent structural studies, with emphasis on the crystallographic structures of complexes involving InhA and inhibitors.

Method::

We start with a literature review, and then we describe recent studies on InhA crystallographic structures. We use this structural information to depict protein-ligand interactions. We also analyze the structural basis for inhibition of InhA. Furthermore, we describe the application of computational methods to predict binding affinity based on the crystallographic position of the ligands.

Results::

Analysis of the structures in complex with inhibitors revealed the critical residues responsible for the specificity against InhA. Most of the intermolecular interactions involve the hydrophobic residues with two exceptions, the residues Ser 94 and Tyr 158. Examination of the interactions has shown that many of the key residues for inhibitor binding were found in mutations of the InhA gene in the isoniazid-resistant Mycobacterium tuberculosis. Computational prediction of the binding affinity for InhA has indicated a moderate uphill relationship with experimental values.

Conclusion::

Analysis of the structures involving InhA inhibitors shows that small modifications on these molecules could modulate their inhibition, which may be used to design novel antitubercular drugs specific for multidrug-resistant strains.

Classification of Mycobacterium tuberculosis DR, MDR,XDR Isolates and Identification of Signature MutationPattern of Drug Resistance

Mycobacterium tuberculosis - a global threat, the recent breakout in MDR-TB and XDR-TB has challenged researchers in diagnosis to provide effective treatment. The main objective to combat drug resistance is to provide rapid, reliable and sensitive diagnostic methods in health care centres. This study focuses on development of an effective pipeline to identify drug resistance mutations in whole genome data of Mycobacterium tuberculosis utilizing the Next Generation Sequencing approach and classification of drug resistance strains based on genetic markers obtained from TGS-TB, tbvar and TBDReamDB. 74 isolates are characterized into 20 DR-TB, 16 MDR-TB, 16 XDR-TB and 6 nonresistant strains based on known drug resistance genetic markers. Results provide mutation pattern for each of the classified strains and profiling of drug resistance to the group of anti-TB drugs. The presence of specific mutation causing resistance to a drug will help set the dosage levels which play an important role in the treatment. Findings on amino acid changes and its respective codon positions in candidate genes will provide insights in drug sensitivity and a way for discovery of potent drugs. The implementation of these approaches in clinical setting provides rapid and sensitive diagnostics to combat the emerging drug resistance.

DNA markers for tuberculosis diagnosis

Tuberculosis (TB), caused by Mycobacterium tuberculosis complex (MTBC), is an infectious disease with more than 10.4 million cases and 1.7 million deaths reported worldwide in 2016. The classical methods for detection and differentiation of mycobacteria are: acid-fast microscopy (Ziehl-Neelsen staining), culture, and biochemical methods. However, the microbial phenotypic characterization is time-consuming and laborious. Thus, fast, easy, and sensitive nucleic acid amplification tests (NAATs) have been developed based on specific DNA markers, which are commercially available for TB diagnosis. Despite these developments, the disease remains uncontrollable. The identification and differentiation among MTBC members with the use of NAATs remains challenging due, among other factors, to the high degree of homology within the members and mutations, which hinders the identification of specific target sequences in the genome with potential impact in the diagnosis and treatment outcomes. In silico methods provide predictive identification of many new target genes/fragments/regions that can specifically be used to identify species/strains, which have not been fully explored. This review focused on DNA markers useful for MTBC detection, species identification and antibiotic resistance determination. The use of DNA targets with new technological approaches will help to develop NAATs applicable to all levels of the health system, mainly in low resource areas, which urgently need customized methods to their specific conditions.