Dual-centre evaluation of the FluoroType MTBDR version 2 assay for detection of Mycobacterium tuberculosis complex and resistance-conferring mutations in pulmonary and extrapulmonary samples from Denmark, Germany and Sierra Leone

OBJECTIVES

We evaluated the ability of FluoroType MTBDR version 2 (FTv2; Hain Lifescience), a second-step real-time PCR assay, to simultaneously detect Mycobacterium tuberculosis complex (MTBC) DNA and mutations conferring resistance to rifampicin (RIF) and isoniazid (INH), in pulmonary and extrapulmonary samples from patients and compared them with corresponding cultures.

METHODS

FTv2 MTBC was evaluated on 1815 and 432 samples from Denmark (DK) and Germany (DE), respectively. RIF and INH resistance mutations were assessed in the German samples and 110 samples from Sierra Leone and subsequently compared to phenotypic antimicrobial susceptibility testing and a composite reference DNA (CRD) based on the GenoType MTBDR line-probe assay and Sanger sequencing or whole-genome sequencing.

RESULTS

Of the 584 (557 smear-negative) Danish and 277 (85 smear-negative) German sputum samples, 42 (16) and 246 (54) were culture positive, and 44 (18) and 222 (35) were FTv2 positive, providing an FTv2 sensitivity and specificity of 0.86 (0.63) and 0.98 (DK), 0.90 (0.65) and 1.00 (DE), respectively. The count, sensitivities, and specificities for all pulmonary samples were 1434, 0.79, and 0.99 (DK) and 347, 0.86, and 1.00 (DE), respectively; for extrapulmonary samples, 381, 0.33, 0.99 (DK) and 83, 0.50, and 1.00 (DE). The valid count, sensitivity, and specificity compared with CRD for detecting resistance mutations were RIF 355, 0.99, 0.96, and INH 340, 1.00, and 0.98, respectively.

DISCUSSION

FTv2 reliably detects MTBC DNA in pulmonary and extrapulmonary samples and detects resistance mutations for INH and RIF resistance in inhA promoter, katG, and rpoB genes.

Isoniazid resistance-conferring mutations are associated with highly variable phenotypic resistance

Background

High-dose isoniazid is recommended in the 9-12 months short-course regimen for multidrug-resistant tuberculosis with inhA mutation. However, there is insufficient evidence to support the assumption of genotypic-phenotypic concordance. This study aimed to identify the genetic mutations associated with high-level phenotypic isoniazid resistance.

Methods

Clinical isolates from patients with drug-resistant tuberculosis were profiled by whole-genome sequencing and subjected to minimum inhibitory concentration (MIC) testing using MGIT based-method. MICs were performed in concentration ranges based on the mutation present: isolates with no isoniazid resistance-conferring mutations and H37Rv, 0.016-0.256 µg/ml; inhA, 0.256-4.0 µg/ml, katG 1.0-16.0 µg/ml; and inhA + katG, 4.0-64.0 µg/ml. Isolates demonstrating resistance at the upper limit of the concentration range were tested up to the maximum of 64.0 µg/ml. Bootstrap of the mean MICs was performed to increase the robustness of the estimates and an overlap index was used to compare the distributions of the MICs for each mutation profile.

Results

A total of 52 clinical isolates were included in this analysis. Bootstrap MIC means for inhA, katG and inhA + katG were 33.64 (95% CI, 9.47, 56.90), 6.79 (4.45, 9.70) and 52.34 (42.750, 61.66) µg/ml, respectively. There was high overlap between inhA and inhA + katG mutations (eta = 0.45) but not with inhA and katG (eta = 0.19). Furthermore, katG showed poor overlap with inhA + katG mutations (eta = 0.09). Unexpectedly, 4/8 (50.0%) of all InhA mutants demonstrated high-level resistance, while 20/24 (83.3%) of katG mutants demonstrated moderate-level resistance.

Conclusions

InhA mutations demonstrated unexpectedly high MICs and showed high overlap with inhA + katG. Contrary to the common belief that katG mutants are associated with high-level resistance, this mutation primarily showed moderate-level resistance.

Exploring natural products library to identify potential inhibitors targeting isoniazid-resistant tuberculosis

Mycobacterium tuberculosis (MTB) causing tuberculosis (TB) infection is a leading source of illness and death in developing nations, and the emergence of drug-resistant TB remains a significant global threat and a challenge in treating the disease. Mutations in the inhA and katG genes are connected to the principal molecular mechanism of isoniazid (INH) resistance, and continuous treatment of INH for more than a decade led to the evolution of INH resistant-TB (inhR-TB). Structure-based drug discovery approaches on traditional natural compounds are the contemporary source to identify significant lead molecules. This work focuses on discovering effective small compounds from natural compound libraries and applying pharmacophore-based virtual screening to filter out the molecules. The best-identified hit complexes were used for molecular dynamics simulations (MDS) to observe their stability and compactness. A three-dimensional e-pharmacophore hypothesis and screening generated 62 hits based on phase fitness scores from the pharmacophore-based virtual screening. Molecular docking experiments in Maestro's GLIDE module indicated that ZINC000002383126 and ASN22022 may be potential inhibitors of inhA and katG (native, inhA mutants S94A, Y158A, Y158F and Y158S and D137S, Y229F, S315T, W321F, and R418L mutants of katG). In addition, MDS analysis indicated that the native and mutant docked complexes of inhA and katG had good stability and remained compact in the binding pocket of the targets. In vitro studies can further validate the compounds that can act as INH competitive inhibitors.Communicated by Ramaswamy H. Sarma.

In vitro modeling of isoniazid resistance mechanisms in Mycobacterium tuberculosis H37Rv

Introduction

Mycobacterium tuberculosis (MTB), the causative agent of tuberculosis, has been a global threat to human beings for several decades. Treating tuberculosis has become more difficult as the prevalence of drug-resistant tuberculosis has increased globally. Evidence suggests that the comprehensive landscape of resistance mechanisms in MTB is ambiguous. More importantly, little is known regarding the series of events connected to resistance mechanisms in MTB before exposure to anti-TB drugs, during exposure to the drugs, and finally, when the MTB becomes resistant after exposure, upon analyses of its genome.

Methods

We used the wild-type strain of MTB (H37Rv) in an in vitro model for generating induced resistance using a sub-inhibitory concentration of isoniazid, and the generated resistance-associated variants (RAVs) were identified using the whole genome sequencing method.

Results

The detection of an inhA promoter mutation (fabG1-15C>T), which results in increased production of InhA protein, was found to be a major mechanism for developing resistance to isoniazid in the first place. We observed adaptation of MTB resistance mechanisms in high isoniazid stress by alteration and abolishment of KatG due to the detection of katG S315N, the common region of mutation that confers isoniazid resistance, along with katG K414N, katG N138S, and katG A162E. Furthermore, we detected the ahpC-72C>T and ahpC 21C>A mutations, but further investigation is needed to determine their role in compensating for the loss of KatG activity.

Discussion

This suggests that increased InhA production is the main mechanism where there are low levels of isoniazid, whereas the alteration of KatG was found to be utilized in mycobacterium with a high concentration of isoniazid. Our work demonstrates that this in vitro approach of generating induced resistance could provide clinically relevant information after the fabG1-15C>T mutation, which is the common mutation found in clinical isolates. Moreover, other mutations detected in this work can also be found in clinical isolates. These findings may shed light on the impact of isoniazid in generating RAV and the resistance mechanism scenario that mycobacterium used under various isoniazid-pressuring conditions. More research is needed to understand better the role of RAV and mechanical resistance events within the mycobacterium genome in promoting a promising drug prediction platform that could lead to the right treatment for patients with MDR-TB and XDR-TB.

Development of DNA Bio-chip for Detection of Mutations of rpoB, embB and inhA Genes in Drug-Resistant Mycobacterium Tuberculosis

Drug-resistant (DR) tuberculosis (TB) is a global threat to health security and TB control programs. Since conventional drug susceptibility testing (DST) takes several weeks, we have developed a molecular method for the rapid identification of DR strains of Mycobacterium Tuberculosis (M.tb) utilizing DNA bio-chips. DNA bio-chips were prepared by immobilizing oligonucleotides (probes) on highly microporous polycarbonate track-etched membranes (PC-TEM) as novel support. Bio-chip was designed to contain 15 specific probes to detect mutations in three genes (rpoB, embB, and inhA). A sensitive and specific chemiluminescence based bio-chip assay was developed based on multiplex PCR followed by hybridization on bio-chip. Fifty culture isolates were used to evaluate the ability of in-house developed bio-chip to detect the mutations. Bio-chip analysis shows that 37.7% of samples show wild type sequences, 53.3% of samples were monoresistance showing resistance to either rifampicin (RMP), isoniazid (INH), or ethambutol (EMB). 4.4% of samples were polydrug resistant showing mutations in both the rpoB gene and embB gene while 4.4% of samples were multidrug-resistant (MDR), harboring mutations in the rpoB and inhA genes. The results were compared with DST and sequencing. Compared to sequencing, bio-chip assay shows a sensitivity of 96.5% and specificity of 100% for RMP resistance. For EMB and INH, the results were in complete agreement with sequencing. This study demonstrates the first-time use of PC-TEMs for developing DNA bio-chip for the detection of mutations associated with drug resistance in M.tb. Developed DNA bio-chip accurately detected different mutations present in culture isolates and thus provides detailed and reliable data for clinical diagnosis.

Detection and characterization of mutations in genes related to isoniazid resistance in Mycobacterium tuberculosis clinical isolates from Iran

BACKGROUND

The global rise in drug-resistant Mycobacterium tuberculosis (M.tb), and especially the significant prevalence of isoniazid (INH)-resistance constitute a significant challenge to global health. Therefore, the present study aimed to investigate mutations in prevalent gene loci-involved in INH-resistance phenotype-among M.tb clinical isolates from southwestern Iran.

METHODS

Drug susceptibility testing (DST) was performed using the conventional proportional method on confirmed 6620 M.tb clinical isolates, and in total, 15 INH-resistant and 18 INH-susceptible isolates were included in the study. Fragments of six genetic loci most related to INH-resistance (katG, inhA promoter, furA, kasA, ndh, oxyR-ahpC intergenic region) were PCR-amplified and sequenced. Mutations were explored by pairwise alignment with the M.tb H37Rv genome.

RESULTS

The analysis of gene loci revealed 13 distinct mutations in INH-resistant isolates. 60% (n = 9) of the INH-resistant isolates had mutations in katG, with codon 315 predominately (53.3%, n = 8). Mutation at InhA - 15 was found in 20% (n = 3) of resistant isolates. 26.7% (n = 4) of the INH-resistant isolates had kasA mutations, of which G269S substitution was the most common (20%, n = 3). The percentage of mutations in furA, oxyR-ahpC and ndh was 6.7% (n = 1), 46.7% (n = 7), and 20% (n = 3), respectively. Of the mutations detected in ndh and oxyR-ahpC, 5 were also observed in INH-susceptible isolates. This study revealed seven novel mutations, four of which were exclusively in resistant isolates.

CONCLUSIONS

This study supports the usefulness of katG and inhA mutations as a predictive molecular marker for INH resistance. Co-detection of katG S315 and inhA-15 mutations identified 73.3% (11 out of 15 isolates) of INH-resistant isolates.

Correlation of inhA mutations and ethionamide susceptibility: Experience from national reference center for tuberculosis

Background:

Detection of ethionamide (ETH) resistance is crucial as it is part of antitubercular regime. It is crucial to examine the role of inhA gene mutations as a surrogate marker for the detection of ETH resistance, in the Indian context. The present retrospective study was designed with this objective.

Subjects and Methods:

The study was conducted in National Reference Laboratory within the tertiary care institute from January 1, 2018, to June 30, 2019, over 18 months duration. A total of 6612 sputum samples from presumptive multidrug-resistant tuberculosis (TB) patients were received from four districts of Delhi, outdoor and inpatients. Line probe assay (LPA) was performed for smear-positive or culture-positive samples for Mycobacterium tuberculosis. All isolates found to be INH resistant by LPA were cultured and phenotypic susceptibility to ETH was conducted for selected isolates as per the guidelines.

Results:

A total of 246 isolates were analyzed, for which phenotypic susceptibility to ETH and mutations in inhA were available. ETH resistance was detected among 87/108 (80.5%) isolates with inhA mutation. Sensitivity and specificity of inhA mutation for detection of ETH resistance were 80.5% and 83.8%, respectively. No inhA mutation was detected in 29/116 (25%) ETH-resistant isolates in our study, whereas ETH was found to be phenotypically susceptible in spite of the presence of inhA mutation among 21/130 (16.1%) isolates.

Conclusions:

Mutations in inhA gene in LPA predict ETH resistance with fairly good sensitivity and specificity. However, it is imperative to perform phenotypic detection of ETH resistance at proper concentration, in addition to detecting inhA mutation.

Significance of the coexistence of non-codon 315 katG, inhA, and oxyR-ahpC intergenic gene mutations among isoniazid-resistant and multidrug-resistant isolates of Mycobacterium tuberculosis: a report of novel mutations

Tuberculosis (TB) is a global threat due to the emergence and spread of drug-resistant Mycobacterium tuberculosis (MTB). Isoniazid (INH) is the main antibiotic used for prevention and treatment of TB. Evidence shows that accumulated mutations can produce INH resistant (INHR) strains, resulting in the progression of multidrug-resistant (MDR) TB. Since point mutations in katG gene, inhA gene, and oxyR-ahpC region correlated with the INH resistance, in this study, we aimed to identify mutations in these three genes in INHR and MDR clinical isolates of MTB by Sanger DNA sequencing analysis. Thirty-three out of 438 isolates were resistant, including 66.7% INHR and 30.3% MDR isolates. In the katG gene, 68.2% INHR isolates had non-synonymous point mutations, mainly R463L (63.6%), and non-synonymous point mutation KatG L587P was seen in one of the MDR isolate. A novel silent substitution L649L was identified in the inhA gene of the MDR isolates. The oxyR-ahpC intergenic region g-88a common mutations (63.6%) in INHR and two distinct novel mutations were found at positions -76 and -77 of the oxyR-ahpC intergenic region. The coexistence of katG non-codon 315 with oxyR-ahpC intergenic region mutations was highly frequent in INHR 59.1% and MDR isolates 70%. Since mutations of all three genes 95.5% lead to the detection of INHR, they might be useful for molecular detection. Our results indicated the continuous evolution and region-specific prevalence of INH resistance. Overall, identification of new mutations in INH resistance can improve the available strategies for diagnosis and control of TB.

The Value of the inhA Mutation Detection in Predicting Ethionamide Resistance Using Melting Curve Technology

Objective

This study aims to analyze the correlation between gene inhA mutations by melting curve technology and phenotypic drug susceptibility (DST) results of ethionamide (ETH), and evaluate whether gene inhA mutations detection can serve as a molecular marker in predicting ETH resistance.

Methods

A retrospective analysis was conducted on 382 strains of Mycobacterium tuberculosis (MTB) with the anti-tuberculosis drugs isoniazid (INH), rifampicin (RIF), ETH, and others. Phenotypic drug susceptibility and the results of inhA and katG genotypes (mutation and no mutation) were obtained using the melting curve technology MeltPro TB assay.

Results

Of the 382 clinical strains of MTB tested, 118 (30.9%) were resistant to INH, and 28 (7.3%) were resistant to ETH. Among the 28 phenotypically ETH-resistant strains, inhA mutations accounted for 42.9% (12/28). These ETH-resistant strains comprise 35.3% (12/34) of the 34 inhA mutant strains. Of 8 single inhA mutation strains (without katG or rpoB mutation), 4(50%) were resistant to INH; however, all of these 8 strains were sensitive to ETH.

Conclusion

The inhA mutation test may not be a reliable predictor of ETH resistance. Mutant inhA strains are not necessarily resistant to ETH. The strains with single inhA mutation (without katG or rpoB mutation) may be effective for ETH treatment. The use of ETH in clinical medicine should be guided by gene (other than inhA alone) detection and phenotypic drug susceptibility testing.

Genetic Mutations Associated with Isoniazid Resistance in Mycobacterium tuberculosis in Mongolia

Globally, mutations in the katG gene account for the majority of isoniazid-resistant strains of Mycobacterium tuberculosis Buyankhishig et al. analyzed a limited number of Mycobacterium tuberculosis strains in Mongolia and found that isoniazid resistance was mainly attributable to inhA mutations (B. Buyankhishig, T. Oyuntuya, B. Tserelmaa, J. Sarantuya, et al., Int J Mycobacteriol 1:40-44, 2012, https://doi.org/10.1016/j.ijmyco.2012.01.007). The GenoType MTBDRplus assay was performed for isolates collected in the First National Tuberculosis Prevalence Survey and the Third Anti-Tuberculosis Drug Resistance Survey to investigate genetic mutations associated with isoniazid resistance in Mycobacterium tuberculosis in Mongolia. Of the 409 isoniazid-resistant isolates detected by the GenoType MTBDRplus assay, 127 (31.1%) were resistant to rifampin, 294 (71.9%) had inhA mutations without katG mutations, 113 (27.6%) had katG mutations without inhA mutations, and 2 (0.5%) had mutations in both the inhA and katG genes. Of the 115 strains with any katG mutation, 114 (99.1%) had mutations in codon 315 (S315T). Of the 296 strains with any inhA mutation, 290 (98.0%) had a C15T mutation. The proportions of isoniazid-resistant strains with katG mutations were 25.3% among new cases and 36.2% among retreatment cases (P = 0.03) and 17.0% among rifampin-susceptible strains and 52.8% among rifampin-resistant strains (P < 0.01). Rifampin resistance was significantly associated with the katG mutation (adjusted odds ratio, 5.36; 95% confidence interval [CI], 3.3 to 8.67, P < 0.001). Mutations in inhA predominated in isoniazid-resistant tuberculosis in Mongolia. However, the proportion of katG mutations in isolates from previously treated cases was higher than in those from new cases, and the proportion in cases with rifampin resistance was higher than in cases without rifampin resistance.

Mutations in rpoB and katG genes and the inhA operon in multidrug-resistant Mycobacterium tuberculosis isolates from Zambia

OBJECTIVES

It is established that resistance to rifampicin (RIF) in 90% of RIF-resistant Mycobacterium tuberculosis isolates is attributable to point mutations in the rpoB gene, whilst 50-95% of M. tuberculosis resistance to isoniazid (INH) is caused by mutations in the katG gene. However, the patterns and frequencies of mutations vary by geographical region. In Zambia, the genetic mechanisms of resistance of M. tuberculosis to RIF and INH were unreported before this study.

METHODS

Using gene sequencing, the rpoB, katG and inhA genes of 99 multidrug-resistant M. tuberculosis (MDR-TB) and 49 pan-susceptible M. tuberculosis isolates stored at a tuberculosis reference laboratory from 2013 to 2016 were analysed and were compared with published profiles from other African countries.

RESULTS

Of the 99 MDR-TB isolates, 95 (96.0%) carried mutations in both rpoB and katG. No mutations were detected among the pan-susceptible isolates. The most common mutations among RIF- and INH-resistant isolates were in codon 531 of the rpoB gene (55.6%; 55/99) and codon 315 of the katG gene (94.9%; 94/99), respectively. Distinctly, katG mutations were predominantly high among Zambian isolates (96.0%) compared with other countries in the region.

CONCLUSION

Resistance-associated mutations to RIF and INH circulating in Zambia are similar to those reported globally, therefore these data validate the applicability of molecular diagnostic tools in Zambia. However, katG mutations were predominantly high among M. tuberculosis isolates in this study compared with other regional countries and might distinguish cross-boundary transmission of MDR-TB from other African nations.

Phenotypic isoniazid resistance and associated mutations in pediatric tuberculosis

BACKGROUND AND OBJECTIVES

Tuberculosis (TB) remains one of the most challenging global health problems as resistance to first-line antimycobacterial drugs continues to rise in many countries worldwide. Isoniazid-resistant TB without MDR-TB poses a serious threat to the management and control of TB across the world. The aim of this study was to investigate the extent of katG315 and inhA-15 mutations in Mycobacterium tuberculosis strains isolated from pediatric TB patients from a tertiary care hospital.

MATERIAL AND METHODS

A total of 51 pulmonary and extra pulmonary specimens were collected from clinically suspected pediatric TB cases, who were microbiologically confirmed. Resistance to INH was detected by 1% proportion method. katG315 and inhA-15 genes were amplified by PCR and detection of mutations in katG315 and inhA-15 genes was done by sequencing.

RESULT

A sample size of only 51 could be achieved due to short duration of the study. 36/51 (70.6%) culture isolates were obtained and put for drug susceptibility test, 5(13.89%) were resistant for isoniazid. M. tuberculosis DNA was found in fifty samples. Mutations in either katG315 or inhA-15 genes were found in 7/50 (14%) samples. Six of seven (85.7%) had mutation in katG315 gene and 1/7 (14.2%) had mutation in inhA-15 gene.

CONCLUSION

INH resistance not only reduces the probability of treatment success, but may also facilitate the spread of MDR-TB and reduce the effectiveness of INH preventive therapy (IPT) therefore quantification of the magnitude of INH resistant TB and variation in frequency of isoniazid resistance associated mutations is important.

Change in prevalence and molecular characteristics of isoniazid-resistant tuberculosis over a 10-year period in China

BACKGROUND

Isoniazid (INH) represents the cornerstone for the treatment of cases infected with Mycobacterium tuberculosis (MTB) strains. Several molecular mechanisms have been shown to be the major causes for INH resistance, while the dynamic change of mutations conferring INH resistance among MTB strains during the past decade is still unknown in China.

METHODS

In this study, we carried out a comparative analysis of the INH minimal inhibitory concentration (MIC) distribution, and investigate the dynamic change of molecular characteristics among INH-resistant MTB strains between 2005 and 2015.

RESULTS

The proportion of INH resistance (39.0%, 105/269) in 2015 was significantly higher than in 2005 (30.0%, 82/273; P = 0.03). Among 269 isolates collected in 2015, 76 (28.3%, 76/269) exhibited high-level INH-resistance (MIC≥32 mg/L), which was significantly higher than that in 2005 (20.5%, 56/273, P = 0.04). In addition, a significantly higher percentage of INH-resistant isolates carried inhA promoter mutations in 2015 (26.7%) versus that in 2005 (14.6%, P = 0.04), while no significant difference was observed in the rates of isolates containing katG mutations between 2005 (76.8%) and 2015 (70.5%, P = 0.33). Notably, the proportion of MTB isolates with inhA mutations (26.7%, 28/105) for patients who had previous exposure to protionamide (PTH) was higher than that for patients who had no previous exposure to PTH (21.4%, 6/28).

CONCLUSIONS

In conclusion, our results demonstrated that the proportion of INH-resistant MTB isolates significantly increased during the last decade, which was mainly attributed to an increase of high-level INH-resistant MTB. In addition, prior exposure to PTH may be associated with the increased frequency of INH-resistant tuberculosis strains with inhA mutations in China.

Computational approach identifies protein off-targets for Isoniazid-NAD adduct: hypothesizing a possible drug resistance mechanism in Mycobacterium tuberculosis

Isoniazid is an important antitubercular molecule identified as a drug of choice in tuberculosis treatment. As such, INH is an inactive prodrug; it acquires an active conformation by forming an adduct with NAD. The adduct targets inhA protein, a reductase responsible for fatty acid chain elongation in the cell wall of Mycobacterium tuberculosis. Resistance to INH is majorly contributed by mutations in inhA, katG and geneic and non-geneic regions associated with efflux genes. Despite being widespread, the mechanism of resistance remains unknown in ∼15% of INH-resistant strains. Studies report that an intracellular increase in NADH concentration prevents inhA inhibition, leading to INH resistance. In the pursuit of finding possible resistance mechanisms, we set out to find NAD binding proteins to explore similarities in structure and NAD binding property of these proteins with that of inhA. We identified 172 NAD binding proteins, of which 53 were identified to have sequence or structural similarity to inhA. By performing docking analysis on selected proteins, we identified INH-adduct to have good binding affinity despite very minimal structural similarity to inhA. This analysis was further supported by principal component analysis, which identified 65 proteins with NAD binding conformation similar to that of inhA. These findings prompt us to hypothesize that upon exposure to INH, bacteria tries to reduce inhA susceptibility by inducing expression of these NAD binding proteins through increase in NADH concentration. This in turn favours off-target binding and leads to decreased binding and potency of INH, thus contributing indirectly to INH resistance.Communicated by Ramaswamy H. Sarma.

rpoB, katG and inhA mutations in multi-drug resistant strains of Mycobacterium tuberculosis clinical isolates from southeast Mexico

INTRODUCTION

Previous knowledge of molecular mechanisms related with multi-drug resistances in tuberculosis is important if molecular diagnostic procedures want to be used in specific geographical regions. For that reason, the aim of this study was to investigate the mutations at rpoB, katG and inhA in multi-drug resistant tuberculosis isolates from Southeast Mexico.

METHODS

Isolates of tuberculosis with a confirmed resistance against rifampicin and isoniazid were collected and sequencing analysis was performed of the rpoB rifampicin resistance-determining region, the katG and the encoding region of inhA.

RESULT

Of 74 isolates with multidrug resistance, 34 (46%) presented six mutations in katG; the most abundant was katG315 in 29 (39%) isolates. At inhA, nine (11%) isolates presented three mutations; the most frequent was inhA21, located in five (6%) strains. Eleven polymorphisms were observed at rpoB in 61 (82%) isolates, prevailing rpoB531 and rpoB 526 in 48 (64%) and ten (12%) isolates, respectively. Eleven double combinations were observed in 39 (52%) isolates, the most common of which was rpoB531+katG315, found in 22 (29%) strains.

CONCLUSION

This study provides valuable information on the diversity of polymorphisms in genes related to multidrug-resistant tuberculosis, as well as the presence of new mutations not previously described; this information should be considered in the implementation of molecular diagnostic tests.

Molecular mechanism of the synergistic activity of ethambutol and isoniazid against Mycobacterium tuberculosis

Isoniazid (INH) and ethambutol (EMB) are two major first-line drugs for managing tuberculosis (TB), caused by the microbe Mycobacterium tuberculosis Although co-use of these two drugs is common in clinical practice, the mechanism for the potential synergistic interplay between them remains unclear. Here, we present first evidence that INH and EMB act synergistically through a transcriptional repressor of the inhA gene, the target gene of INH encoding an enoyl-acyl carrier protein reductase of the fatty acid synthase type II system required for bacterial cell wall integrity. We report that EMB binds a hypothetical transcription factor encoded by the Rv0273c gene, designated here as EtbR. Using DNA footprinting, we found that EtbR specifically recognizes a motif sequence in the upstream region of the inhA gene. Using isothermal titration calorimetry and surface plasmon resonance assays, we observed that EMB binds EtbR in a 1:1 ratio and thereby stimulates its DNA-binding activity. When a nonlethal dose of EMB was delivered in combination with INH, EMB increased the INH susceptibility of cultured M. tuberculosis cells. In summary, EMB induces EtbR-mediated repression of inhA and thereby enhances the mycobactericidal effect of INH. Our findings uncover a molecular mechanism for the synergistic activity of two important anti-TB drugs.

Significance of Coexisting Mutations on Determination of the Degree of Isoniazid Resistance in Mycobacterium tuberculosis Strains

The emergence and spread of drug-resistant tuberculosis (TB) pose a threat to TB control in Sri Lanka. Isoniazid (INH) is a key element of the first-line anti-TB treatment regimen. Resistance to INH is mainly associated with point mutations in katG, inhA, and ahpC genes. The objective of this study was to determine mutations of these three genes in INH-resistant Mycobacterium tuberculosis (MTb) strains in Sri Lanka. Complete nucleotide sequence of the three genes was amplified by polymerase chain reaction and subjected to DNA sequencing. Point mutations in the katG gene were identified in 93% isolates, of which the majority (78.6%) were at codon 315. Mutations at codons 212 and 293 of the katG gene have not been reported previously. Novel mutations were recognized in the promoter region of the inhA gene (C deletion at -34), fabG1 gene (codon 27), and ahpC gene (codon 39). Single S315T mutation in the katG gene led to a high level of resistance, while a low level of resistance with high frequency (41%) was observed when katG codon 315 coexisted with the mutation at codon 463. Since most of the observed mutations of all three genes coexisted with the katG315 mutation, screening of katG315 mutations will be a useful marker for molecular detection of INH resistance of MTb in Sri Lanka.

Mutations of rpoB, katG, inhA and ahp genes in rifampicin and isoniazid-resistant Mycobacterium tuberculosis in Kyrgyz Republic

Background

The aim of this study was to identify mutations of rpoB, katG, inhA and ahp-genes associated Mycobacterium tuberculosis resistance to rifampicin (RIF) and isoniazid (INH) in Kyrgyz Republic. We studied 633 smear samples from the primary pulmonary tuberculosis (TB) patients. We verified Mycobacterium tuberculosis susceptibility to RIF and INH using culture method of absolute concentrations, and commercially available test named “TB-BIOCHIP” (Biochip-IMB, Moscow, Russian Federation).

Results

For RIF-resistance, TB-BIOCHIP’s sensitivity and specificity were 88% and 97%, 84% and 95% for INH-resistance, and 90% and 97% for multi-drug resistance (MDR). In RIF-resistant strains, TB-BIOCHIP showed mutations in codons 531 (64.8%), 526 (17.3%), 516 (8.1%), 511 (5.4%), 533 (3.2%), 522 (0.6%) and 513 (0.6%) of rpoB gene. The most prevalent was Ser531 > Leu mutation (63.7%). 91.2% of mutations entailing resistance to INH were in katG gene, 7% in inhA gene, and 1.8% in ahpC gene. Ser315→Thr (88.6%) was the most prevalent mutation leading to resistance to INH.

Conclusions

In Kyrgyz Republic, the most prevalent mutation in RIF-resistant strains was Ser531 → Leu in rpoB gene, as opposed to Ser315 → Thr in katG gene in INH-resistant Mycobacterium tuberculosis. In Kyrgyz Republic, the major reservoir of MDR Mycobacterium tuberculosis were strains with combined mutations Ser531 → Leu in rpoB gene and Ser315 → Thr in katG gene. TB-BIOCHIP has shown moderate sensitivity with the advantage of obtaining results in only two days.

Genotypic characterization of drug resistant Mycobacterium tuberculosis in Quebec, 2002-2012

Background

The increasing emergence of drug-resistant tuberculosis presents a threat to the effective control of tuberculosis (TB). Rapid detection of drug-resistance is more important than ever to address this scourge. The purpose of this study was to genotypically characterize the first-line antitubercular drug-resistant isolates collected over 11 years in Quebec.

Results

The main mutations found in our resistant strains collection (n = 225) include: the S315T substitution in katG (50.2 %), the -15 C/T mutation in the inhA promoter (29 %); the S531L substitution in rpoB (43 %); the deletion 8 bp 446 / + R140S in pncA (72.9 %); the M306I (35.7 %) and M306V (21.4 %) substitutions in embB. Ten of the mutations in katG and 4 mutations identified in pncA were previously undescribed.

Conclusion

Screening of mutations conferring resistance to first-line antituberculous drugs using DNA-sequencing approach seems to be feasible and would drastically shorten the time to determine the resistance profile compared to the proportion method.

Development of a Mycobacterium smegmatis transposon mutant array for characterising the mechanism of action of tuberculosis drugs: Findings with isoniazid and its structural analogues

The development of new drugs is required to control human tuberculosis (TB). This study examined whether drug hypersensitive mutants could be used to reveal novel aspects of the mechanism of action of a TB drug. A transposon mutant collection with an estimated 1.1-fold genome coverage (7680 mutants) was constructed in Mycobacterium smegmatis and screened in high-throughput against isoniazid. Hypersensitive transposants with mutations in genes known to influence the mode of action of isoniazid were isolated. To further investigate the role of one of these genes, nudC, the corresponding mutant was tested for sensitivity towards isoniazid structural analogues. Overexpression of nudC, as well as inhA which encodes a known target of isoniazid, increased M. smegmatis resistance to isoniazid, but failed to increase resistance to three of the analogues, NSC27607, NSC33759, and NSC40350. In contrast, overexpression of katG resulted in increased sensitivity to each of the isoniazid analogues tested including NSC27607, NSC33759, and NSC40350. This provides evidence that the latter isoniazid analogues are activated by KatG in a NudC-independent manner and that InhA may not be their primary target. In summary, characterisation of drug hypersensitive mutants detected genes involved in the mode of action of isoniazid. Furthermore, it identified isoniazid analogues which are resilient to both InhA- and NudC-dependent mechanisms of resistance.

Detection of novel and reported mutations in the rpoB, katG and inhA genes in multidrug-resistant tuberculosis isolates: A hospital-based study

The objective of this study was to detect mutations associated with isoniazid (INH) and rifampicin (RIF) resistance in Mycobacterium tuberculosis isolates from newly diagnosed and previously treated tuberculosis patients using a PCR-based DNA sequencing technique. Phenotypic drug susceptibility testing was performed using a BACTEC™ MicroMGIT Culture System in 354 M. tuberculosis isolates. Among the 354 isolates, 18 were multidrug-resistant tuberculosis (MDR-TB). PCR-based DNA sequencing was performed targeting the rpoB gene for RIF and the whole of the katG gene and the promoter and coding region of the inhA gene for INH. Results were analysed using MultAlin analysis to identify the presence of polymorphisms or mutations by comparing with already available GenBank sequences. Only 37.5% of RIF-resistant isolates showed the presence of the most commonly reported mutation (Ser531Leu). The most commonly reported mutation (Ser531Leu) was detected in six MDR-TB isolates. The frequency of mutations associated with INH resistance was 31.5% (17/54) and 29.6% (16/54) for katG and inhA, respectively. Comparing the relative distribution of mutations in the two target loci revealed that 12 isolates (22.2%) had a mutation in both katG and inhA. Apart from previously reported mutations in the katG gene, there were three novel deletion and six novel substitution mutations. As reported in previous studies, Ser531Leu was the most common mutation detected in RIF-resistant isolates. The genetic mechanism of INH resistance in M. tuberculosis is highly complex involving several genes, and much remains to be explored to achieve a better understanding of this complex mechanism.