Molecular mechanism of rifampicin and isoniazid resistance in Mycobacterium tuberculosis from Bangladesh

Evolution of tuberculosis diagnostics: From molecular strategies to nanodiagnostics

Tuberculosis has remained a global concern for public health affecting the lives of people for ages. Approximately 10 million people are affected by the disease and 1.5 million succumb to the disease worldwide annually. The COVID-19 pandemic has highlighted the role of early diagnosis to win the battle against such infectious diseases. Thus, advancement in the diagnostic approaches to provide early detection forms the foundation to eradicate and manage contagious diseases like tuberculosis. The conventional diagnostic strategies include microscopic examination, chest X-ray and tuberculin skin test. The limitations associated with sensitivity and specificity of these tests demands for exploring new techniques like probe-based assays, CRISPR-Cas and microRNA detection. The aim of the current review is to envisage the correlation between both the conventional and the newer approaches to enhance the specificity and sensitivity. A significant emphasis has been placed upon nanodiagnostic approaches manipulating quantum dots, magnetic nanoparticles, and biosensors for accurate diagnosis of latent, active and drug-resistant TB. Additionally, we would like to ponder upon a reliable method that is cost-effective, reproducible, require minimal infrastructure and provide point-of-care to the patients.

Characterization of Genetic Variants Associated with Rifampicin Resistance Level in Mycobacterium tuberculosis Clinical Isolates Collected in Guangzhou Chest Hospital, China

Objective

Rifampicin (RIF)-resistance, a surrogate marker for multidrug-resistant tuberculosis (TB), is mediated by mutations in the rpoB gene. We aimed to investigate the prevalence of mutations pattern in the entire rpoB gene of Mycobacterium tuberculosis clinical isolates and their association with resistance level to RIF.

Methods

Among 465 clinical isolates collected from the Guangzhou Chest Hospital, drug-susceptibility of 175 confirmed Mtb strains was performed via the proportion method and Bactec MGIT 960 system. GeneXpert MTB/RIF and sanger sequencing facilitated in genetic characterization, whereas the MICs of RIF were determined by Alamar blue assay.

Results

We found 150/175 (85.71%) RIF-resistant strains (MIC: 4 to >64 µg/mL) of which 57 were MDR and 81 pre-XDR TB. Genetic analysis identified 17 types of mutations 146/150 (97.33%) within RRDR (codons 426–452) of rpoB, mainly at L430 (P), D435 (V, E, G, N), H445 (N, D, Y, R, L), S450 (L, F) and L452 (P). D435V 12/146 (8.2%), H445N 16/146 (10.9%), and S450L 70/146 (47.94%) were the most frequently encountered mutations. Mutations Q432K, M434V, and N437D are rarely identified in RRDR. Deletions at (1284–1289 CCAGCT), (1295–1303 AATTCATGG), and insertion at (1300–1302 TTC) were detected within RRDR of three RIF^R strains for the first time. We detected 47 types of mutations and insertions/deletions (indels) outside the RRDR. Four RIF^R strains were detected with only novel mutations/indels outside the RRDR. Two of the four had (K274Q + C897 del + I491M) and (A286V + L494P), respectively. The other two had (G1687del + P454L) and (TT1835-6 ins + I491L) individually. Compared with phenotypic characterization, diagnostic sensitivities of GeneXpert MTB/RIF and sequencing analysis were 95.33% (143/150), and 100% (150/150) respectively.

Conclusion

Our findings underscore the key role of RRDR mutations and the contribution of non-RRDR mutations in rapid molecular diagnosis of RIF^R clinical isolates. Such insights will support early detection of disease and recommend the appropriate anti-TB regimens in high-burden settings.

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.

Rapid and Simple Detection of Isoniazid-Resistant Mycobacterium tuberculosis Utilizing a DNA Chromatography-Based Technique

Despite the availability of anti-tuberculosis drugs, the treatment of tuberculosis has been complicated by drug-resistant tuberculosis. The early detection of drug resistance makes early treatment possible. However, the available tools are mainly for rifampicin resistance detection, and the existing isoniazid resistance detection method is expensive, highly technical, and complicated, making it unsustainable for use in developing nations. This study aimed to develop a simple, rapid, and low-cost diagnostic kit for isoniazid-resistant tuberculosis using the single-stranded tag hybridization method to target an isoniazid resistance-conferring mutation. Specificity and sensitivity were assessed using DNA extracted from 49 isoniazid-resistant and 41 isoniazid-susceptible Mycobacterium tuberculosis clinical isolates cultured in mycobacterial growth indicator tubes. Positive signals were observed on mutant and wild-type lines with 100% sensitivity and specificity compared with Sanger sequencing results. In contrast, no positive signal was observed for non-tuberculosis mycobacteria. The detection limit of this method was 10³ CFU or less. The STH-PAS system for isoniazid-resistant M. tuberculosis detection developed in this study offers a better alternative to conventional phenotypic isoniazid resistance determination, which will be of both clinical and epidemiological significance in resource-limited nations.

Rapid detection of rifampicin-resistant Mycobacterium tuberculosis, based on isothermal DNA amplification and DNA chromatography

Rapid and easy detection of nucleotide point mutations in bacterial pathogens associated with drug resistance is essential for the proper use of antimicrobials. Here, we developed a rapid and simple method for the detection of mutations using Loop-mediated isothermal amplification (LAMP) combined with the single-tag hybridization (STH) chromatographic printed array strips (PAS) method. This procedure is able to detect four mutations (C1349 T, A1295C, G1303 T, A1304 T) in Rifampicin Resistance Determining Region (RRDR) of rifampicin-resistant Mycobacterium tuberculosis (RR-TB), simultaneously. LAMP reactions contained a LAMP primer and eight allele-specific primers for each mutation. The allele-specific primers products were detected by nucleic acid chromatography using PAS. Four detection lines were detected there, one of which was detected at different positions depend on the wild type and the mutant type. We carried out the four mutations detection using 31 genomic DNA (2 A1295T, 1 G1303 T, 6 A1304 T, 22 C1349 T) from clinical isolate. The mutations have been confirmed by sequence analysis. The detection results were completely consistent with the sequence analysis. In the present study, four mutations could be detected, but only 60% of RR-TB could be detected with these four. It is expected that the detection rate will increase by adding more mutant primers. The combined LAMP and STH chromatographic PAS method is a simple and rapid method for detecting point mutations in clinical isolates as a point-of-care testing (POCT) technique. In addition, it does not require special equipment and can meet the demand in areas where drug-resistant bacteria are endemic, such as developing countries.

Distribution and Frequency of rpoB Mutations Detected by Xpert MTB/RIF Assay Among Beijing and Non-Beijing Rifampicin Resistant Mycobacterium tuberculosis Isolates in Bangladesh

Background

Rifampicin resistance (RR) is a key indicator of multidrug-resistant tuberculosis (MDR-TB) and 95% of the RR is associated with the mutation in the 81-bp rifampicin resistance determining region (RRDR) of the rpoB gene of Mycobacterium tuberculosis complex (MTBC). The Xpert MTB/RIF (Xpert) assay uses five overlapping molecular beacon probes (A-E) complementary to RRDR region that detect MTBC and mutations associated with RR. The objective of the study was to investigate the distribution and frequency of mutations detected by Xpert assay among Beijing and non-Beijing RR-TB isolates.

Methods

A total of 205 randomly selected RR-TB specimens detected by Xpert assay were included in this study. A portion of specimens was further subjected to culture, MTBDRplus test and the positive culture isolates were genotyped by spoligotyping.

Results

We found that the most frequent mutation occurred at probe E (S531L) binding region in both Beijing and non-Beijing isolates (61.9% and 66.9%, respectively). The Beijing family had higher mutation rates than non-Beijing (19.0% vs 12.4%) at probe B (D516V) while the non-Beijing family had higher mutations at probe D (H526D or H526Y) than the Beijing (13.2% vs 10.7%) family. Mutations at probes Aand C were less common in both Beijing and non-Beijing isolates. There was no significant difference (P=0.36) in the occurrence of mutations at different probes between Beijing and non-Beijing isolates.

Conclusions

The study results revealed that the most frequent mutation occurs in the region of probe E and the least common mutations at probe A and C among both Beijing and non-Beijing RR-TB cases. This first insight into the probe mutation variation and frequencies among the RR-TB cases in Bangladesh forms the baseline information for further investigation.

Potentially High Number of Ineffective Drugs with the Standard Shorter Course Regimen for Multidrug-Resistant Tuberculosis Treatment in Haiti

Multidrug-resistant tuberculosis (MDR-TB) outcomes are poor partly because of the long treatment duration; the World Health Organization conditionally recommends a shorter course regimen to potentially improve treatment outcomes. Here, we describe the drug susceptibility patterns of a cohort of MDR-TB patients in Haiti and determine the number of likely effective drugs if they were treated with the recommended shorter course regimen. We retrospectively examined drug susceptibility patterns of adults initiating MDR-TB treatment between 2008 and 2015 at the Haitian Group for the Study of Kaposi's Sarcoma and Opportunistic Infections in Port-au-Prince, Haiti. First- and second-line drug susceptibility testing (DST) was analyzed and used to determine the number of presumed effective drugs. Of the 239 patients analyzed, 226 (95%), 183 (77%), 135 (57%), and 38 (16%) isolates were resistant to high-dose isoniazid, ethambutol, pyrazinamide, and ethionamide, respectively. Eight patients (3%) had resistance to either a fluoroquinolone or a second-line injectable and none had extensively resistant TB. Of the 239 patients, 132 (55%) would have fewer than five likely effective drugs in the intensive phase of the recommended shorter course regimen and 121 (51%) would have two or fewer likely effective drugs in the continuation phase. Because of the high rates of resistance to first-line TB medications, about 50% of MDR-TB patients would be left with only two effective drugs in the continuation phase of the recommended shorter course regimen, raising concerns about the effectiveness of this regimen in Haiti and the importance of using DST to guide treatment.

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.

Characterization of Mutations Conferring Resistance to Rifampin in Mycobacterium tuberculosis Clinical Strains

Resistance of Mycobacterium tuberculosis to rifampin (RMP), mediated by mutations in the rpoB gene coding for the beta-subunit of RNA polymerase, poses a serious threat to the efficacy of clinical management and, thus, control programs for tuberculosis (TB). The contribution of many individual rpoB mutations to the development and level of RMP resistance remains elusive. In this study, the incidence of mutations throughout the rpoB gene among 115 Mycobacterium tuberculosis clinical isolates, both resistant and susceptible to RMP, was determined. Of the newly discovered rpoB mutations, the role of three substitutions in the causation of RMP resistance was empirically tested. The results from in vitro mutagenesis experiments were combined with the assessment of the prevalence of rpoB mutations, and their reciprocal co-occurrences, across global M. tuberculosis populations. Twenty-two different types of mutations in the rpoB gene were identified and distributed among 58 (89.2%) RMP-resistant strains. The MICs of RMP were within the range of 40 to 800 mg/liter, with MIC₅₀ and MIC₉₀ values of 400 and 800 mg/liter, respectively. None of the mutations (Gln429His, Met434Ile, and Arg827Cys) inspected for their role in the development of RMP resistance produced an RMP-resistant phenotype in isogenic M. tuberculosis H37Rv strain-derived mutants. These mutations are supposed to compensate for fitness impairment incurred by other mutations directly associated with drug resistance.

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.

High diversity of multidrug-resistant Mycobacterium tuberculosis Central Asian Strain isolates in Nepal

OBJECTIVES

Tuberculosis (TB) caused by Mycobacterium tuberculosis (MTB) poses a major public health problem in Nepal. Although it has been reported as one of the dominant genotypes of MTB in Nepal, little information on the Central Asian Strain (CAS) family is available, especially isolates related to multidrug resistance (MDR) cases. This study aimed to elucidate the genetic and epidemiological characteristics of MDR CAS isolates in Nepal.

METHODS

A total of 145 MDR CAS isolates collected in Nepal from 2008 to 2013 were characterized by spoligotyping, mycobacterial interspersed repetitive unit-variable number tandem repeat (MIRU-VNTR) analysis, and drug resistance-associated gene sequencing.

RESULTS

Spoligotyping analysis showed CAS1_Delhi SIT26 as predominant (60/145, 41.4%). However, by combining spoligotyping and MIRU-VNTR typing, it was possible to successfully discriminate all 145 isolates into 116 different types including 18 clusters with 47 isolates (clustering rate 32.4%). About a half of these clustered isolates shared the same genetic and geographical characteristics with other isolates in each cluster, and some of them shared rare point mutations in rpoB that are thought to be associated with rifampicin resistance.

CONCLUSIONS

Although the data obtained show little evidence that large outbreaks of MDR-TB caused by the CAS family have occurred in Nepal, they strongly suggest several MDR-MTB transmission cases.

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.

Resistance to Isoniazid and Ethionamide in Mycobacterium tuberculosis: Genes, Mutations, and Causalities

Isoniazid (INH) is the cornerstone of tuberculosis (TB) chemotherapy, used for both treatment and prophylaxis of TB. The antimycobacterial activity of INH was discovered in 1952, and almost as soon as its activity was published, the first INH-resistant Mycobacterium tuberculosis strains were reported. INH and its structural analog and second-line anti-TB drug ethionamide (ETH) are pro-drugs. INH is activated by the catalase-peroxidase KatG, while ETH is activated by the monooxygenase EthA. The resulting active species reacts with NAD+ to form an INH-NAD or ETH-NAD adduct, which inhibits the enoyl ACP reductase InhA, leading to mycolic acid biosynthesis inhibition and mycobacterial cell death. The major mechanism of INH resistance is mutation in katG, encoding the activator of INH. One specific KatG variant, S315T, is found in 94% of INH-resistant clinical isolates. The second mechanism of INH resistance is a mutation in the promoter region of inhA (c-15t), which results in inhA overexpression and leads to titration of the drug. Mutations in the inhA open reading frame and promoter region are also the major mechanism of resistance to ETH, found more often in ETH-resistant clinical isolates than mutations in the activator of ETH. Other mechanisms of resistance to INH and ETH include expression changes of the drugs' activators, redox alteration, drug inactivation, and efflux pump activation. In this article, we describe each known mechanism of resistance to INH and ETH and its importance in M. tuberculosis clinical isolates.

Genotypic characterization of multi-drug-resistant Mycobacterium tuberculosis isolates in Myanmar

The number of multi-drug-resistant tuberculosis (MDR-TB) cases is rising worldwide. As a countermeasure against this situation, the implementation of rapid molecular tests to identify MDR-TB would be effective. To develop such tests, information on the frequency and distribution of mutations associating with phenotypic drug resistance in Mycobacterium tuberculosis is required in each country. During 2010, the common mutations in the rpoB, katG and inhA of 178 phenotypically MDR M. tuberculosis isolates collected by the National Tuberculosis Control Program (NTP) in Myanmar were investigated by DNA sequencing. Mutations affecting the 81-bp rifampicin (RIF) resistance-determining region (RRDR) of the rpoB were identified in 127 of 178 isolates (71.3%). Two of the most frequently affected codons were 531 and 526, with percentages of 48.3% and 14.0% respectively. For isoniazid (INH) resistance, 114 of 178 MDR-TB isolates (64.0%) had mutations in the katG in which a mutation-conferring amino acid substitution at codon 315 from Ser to Thr was the most common. Mutations in the inhA regulatory region were also detected in 20 (11.2%) isolates, with the majority at position -15. Distinct mutation rate and pattern from surrounding countries might suggest that MDR-TB has developed and spread domestically in Myanmar.

Occurrence of diverse mutations in isoniazid- and rifampicin-resistant Mycobacterium tuberculosis isolates from autochthonous and immigrant populations of Saudi Arabia

For the first time in Saudi Arabia, the impact of a patient's ethnic background on mutations conferring resistance to rifampicin (RIF) and isoniazid (INH) in Mycobacterium tuberculosis isolates was analyzed on a nationwide sample collection. Four hundred fifteen isolates were subjected to drug susceptibility testing, mutation analysis, spoligotyping, and 24 loci-based Mycobacterial Interspersed Repetitive Units-Variable Number Tandem Repeat typing, respectively. Phenotypically, 41 (9.9%) isolates were resistant to RIF, 239 (57.6%) to INH, and 135 (32.5%) to both RIF and INH, respectively. Forty (9.6%), 236 (56.8%), and 133 (32%) isolates were determined as resistant to RIF, INH, and to both by molecular assay. Codon 531 (S531L) mutations (69.4%) in the rpoB gene and codon 315 (S315T) mutations (67.2%) in the katG gene were the most prominent among RIF- and INH-resistant isolates, respectively. The autochthonous population showed a predominance of rpoB codon 516 and 526 mutations, while the inhA promoter position -15 and -8 mutations were prominent among immigrants. A strain cluster ratio of 32% (30 clusters) was observed and 24 clusters displayed identical mutations. Overall, Euro-American lineages were predominant. However, Beijing (56.7%) and EAI (42.7%) were noticed with the highest cluster rate. In Saudi Arabia, the occurrence of mutations responsible for INH and RIF resistance was significantly associated with the ethnic origin of the patient.

Isolation and characterization of compound-resistant isolates of Mycobacterium tuberculosis

This chapter describes the isolation and characterization of spontaneous resistant mutants of Mycobacterium tuberculosis. The overall objective of resistant mutant isolation is to determine the mode of action and/or cellular targets of new antimycobacterial agents. Whole-genome sequencing of resistant mutants can identify targets of antimycobacterial drugs and mechanisms of resistance, such as efflux, changes in drug permeability, or drug recognition. Mutants allow insight into in vivo biological processes and can help elucidate the number and identity of genes in a given pathway. Resistant mutant characterization can also lay the groundwork for structure/function studies, especially in conjunction with binding studies and X-ray crystallography.

Comprehensive phenotypic characterization of rifampicin resistance mutations in Salmonella provides insight into the evolution of resistance in Mycobacterium tuberculosis

OBJECTIVES

Mutations in the β-subunit of RNA polymerase (RNAP), encoded by rpoB, are responsible for rifampicin resistance (Rif(R)). Although many mutations in rpoB can reduce susceptibility, only a few are frequent amongst Rif(R) clinical Mycobacterium tuberculosis (MTB) isolates. It has been suggested that there is a negative correlation between the fitness costs of Rif(R) mutations and their respective clinical frequency, but so far comparable fitness cost measurements have only been conducted for a very limited number of Rif(R) mutations. We tested this hypothesis using Salmonella and Mycobacterium smegmatis as model organisms.

METHODS

We constructed 122 different Rif(R) mutations in Salmonella. MICs and relative fitness costs in the presence and absence of rifampicin were determined for each mutant, including for a smaller number of Rif(R) M. smegmatis strains. Results were compared with available mutation frequency data from clinical MTB isolates.

RESULTS

(i) Rif(R) mutations frequently found in MTB isolates have a fitness cost in Salmonella Typhimurium and M. smegmatis. (ii) Clinically frequent Rif(R) mutations have a high rifampicin MIC. (iii) There is a strong correlation between the magnitude of the fitness cost of a Rif(R) mutation in Salmonella Typhimurium or M. smegmatis and the frequency with which that mutation is associated with secondary (putative compensatory) mutations in RNAP of clinical MTB isolates.

CONCLUSIONS

This suggests that the success of Rif(R) mutations in clinical MTB isolates may be dependent not only on a low initial fitness cost, but rather the results of three factors: (i) a high rifampicin MIC; (ii) a relatively low initial fitness cost; and (iii) the ability to additionally acquire compensatory mutations selected to further reduce fitness cost.

The mutations of katG and inhA genes of isoniazid-resistant Mycobacterium tuberculosis isolates in Taiwan

BACKGROUND/PURPOSE

The isoniazid (INH) resistance of Mycobacterium tuberculosis is caused by mutations in the katG and inhA genes encoding for catalase-peroxidase and inhA, respectively. Sequences of the katG and inhA gene of 70 isolates were analyzed to identify the mutations and to compare the mutations with their related susceptibilities.

METHODS

Sequences of the katG and inhA genes and the resistance profiles were analyzed for the 70 M. tuberculosis isolates, collected from nine hospitals in Taiwan during the period from 1999 to 2011.

RESULTS

Fifteen alleles were identified in the katG gene and two alleles were identified in the inhA gene. Among the 15 alleles identified in the katG gene, 14 alleles were found in isolates resistant to isoniazid, while only three alleles were found in isolates susceptible to isoniazid. The mutations of the katG gene and their frequencies of 41 INH-resistant isolates were Arg463Leu (51%), Ser315Thr (29%), Ser315Asn (9.8%), and other loci (22%). The sensitivity and specificity of the Ser315Thr mutation for the detection of INH-resistant isolates were 29% and 100%, respectively. The frequency of inhA gene mutation was low (2.44%) in the 41 INH-resistant isolates.

CONCLUSION

The diverse alleles of the katG gene associated with INH resistance are present in the M. tuberculosis isolates in Taiwan. These data may be applied to develop new probes for various alleles associated with INH resistance in order to increase the sensitivity for the detection of genetically diverse M. tuberculosis isolates in different geographic areas. The diversity of mutations can also provide information for investigating the evolutional lineages of M. tuberculosis isolates.

Manganese(II) complexes with thiosemicarbazones as potential anti-Mycobacterium tuberculosis agents

Through a systematic variation on the structure of a series of manganese complexes derived from 2-acetylpyridine-N(4)-R-thiosemicarbazones (Hatc-R), structural features have been investigated with the aim of obtaining complexes with potent anti-Mycobacterium tuberculosis activity. The analytical methods used for characterization included FTIR, EPR, UV-visible, elemental analysis, cyclic voltammetry, magnetic susceptibility measurement and single crystal X-ray diffractometry. Density functional theory (DFT) calculations were performed in order to evaluate the contribution of the thiosemicarbazonate ligands on the charge distribution of the complexes by changing the peripheral groups as well as to verify the Mn-donor atoms bond dissociation predisposition. The results obtained are consistent with the monoanionic N,N,S-tridentate coordination of the thiosemicarbazone ligands, resulting in octahedral complexes of the type [Mn(atc-R)2], paramagnetic in the extension of 5 unpaired electrons, whose EPR spectra are consistent for manganese(II). The electrochemical analyses show two nearly reversible processes, which are influenced by the peripheral substituent groups at the N4 position of the atc-R(1-) ligands. The minimal inhibitory concentration (MIC) of these compounds against M. tuberculosis as well as their in vitro cytotoxicity on VERO and J774A.1 cells (IC50) was determined in order to find their selectivity index (SI) (SI=IC50/MIC). The results evidenced that the compounds described here can be considered as promising anti-M. tuberculosis agents, with SI values comparable or better than some commercial drugs available for the tuberculosis treatment.

Simple multiplex PCR assay for identification of Beijing family Mycobacterium tuberculosis isolates with a lineage-specific mutation in Rv0679c

The Beijing genotype of Mycobacterium tuberculosis is known to be a worldwide epidemic clade. It is suggested to be a possibly resistant clone against BCG vaccination and is also suggested to be highly pathogenic and prone to becoming drug resistant. Thus, monitoring the prevalence of this lineage seems to be important for the proper control of tuberculosis. The Rv0679c protein of M. tuberculosis has been predicted to be one of the outer membrane proteins and is suggested to contribute to host cell invasion. Here, we conducted a sequence analysis of the Rv0679c gene using clinical isolates and found that a single nucleotide polymorphism, C to G at position 426, can be observed only in the isolates that are identified as members of the Beijing genotype family. Here, we developed a simple multiplex PCR assay to detect this point mutation and applied it to 619 clinical isolates. The method successfully distinguished Beijing lineage clones from non-Beijing strains with 100% accuracy. This simple, quick, and cost-effective multiplex PCR assay can be used for a survey or for monitoring the prevalence of Beijing genotype M. tuberculosis strains.