Drug Resistance Pattern of Mycobacterium tuberculosis Isolates From Patients Referred to TB Reference Laboratory in Ahvaz

Epidemiology of first- and second-line drugs-resistant pulmonary tuberculosis in Iran: Systematic review and meta-analysis

Drug resistance among Mycobacterium tuberculosis (MTB) strains is a growing concern in developing countries. We conducted a comprehensive search for relevant studies in Iran on PubMed, Scopus, and Embase until June 12, 2020. Our study focused on determining the prevalence of antibiotic resistance in MTB isolates, with subgroup analyses based on year, location, and drug susceptibility testing (DST) methods. Statistical analyses were performed using STATA software. Our meta-analysis included a total of 47 articles. Among new TB cases, we found the following prevalence rates: Any-resistance to first-line drugs: 31 % (95 % CI, 24-38), mono-drug resistance: 15 % (95 % CI, 10-22), and multidrug resistance to first-line drugs: 6 % (95 % CI, 4-8). There was a significant variation in the rate of MDR among new TB cases based on the year of publication, location, and DST methods (P < 0.0001). We observed substantial variability in multidrug-resistant TB rates among new cases across the studies. Stratified analyses revealed that publication years and DST methods significantly affected resistance rates. Studies from southern and central Iran reported higher any-drug resistance rates, suggesting regional differences. Among retreatment cases, the prevalence rates were as follows: Any resistance: 68 % (95 % CI 58-78), mono-resistance: 19 % (95 % CI 7-34), multidrug resistance: 28 % (95 % CI 15-43). Our study revealed that the prevalence of drug-resistant TB (DR-TB) among TB cases in Iran is higher than the global average. Particularly, MDR-TB among retreatment TB cases is a significant public health issue.

The Structural Basis of Mycobacterium tuberculosis RpoB Drug-Resistant Clinical Mutations on Rifampicin Drug Binding

Tuberculosis (TB), caused by the Mycobacterium tuberculosis infection, continues to be a leading cause of morbidity and mortality in developing countries. Resistance to the first-line anti-TB drugs, isoniazid (INH) and rifampicin (RIF), is a major drawback to effective TB treatment. Genetic mutations in the β-subunit of the DNA-directed RNA polymerase (rpoB) are reported to be a major reason of RIF resistance. However, the structural basis and mechanisms of these resistant mutations are insufficiently understood. In the present study, thirty drug-resistant mutants of rpoB were initially modeled and screened against RIF via a comparative molecular docking analysis with the wild-type (WT) model. These analyses prioritized six mutants (Asp441Val, Ser456Trp, Ser456Gln, Arg454Gln, His451Gly, and His451Pro) that showed adverse binding affinities, molecular interactions, and RIF binding hinderance properties, with respect to the WT. These mutant models were subsequently analyzed by molecular dynamics (MD) simulations. One-hundred nanosecond all-atom MD simulations, binding free energy calculations, and a dynamic residue network analysis (DRN) were employed to exhaustively assess the impact of mutations on RIF binding dynamics. Considering the global structural motions and protein-ligand binding affinities, the Asp441Val, Ser456Gln, and His454Pro mutations generally yielded detrimental effects on RIF binding. Locally, we found that the electrostatic contributions to binding, particularly by Arg454 and Glu487, might be adjusted to counteract resistance. The DRN analysis revealed that all mutations mostly distorted the communication values of the critical hubs and may, therefore, confer conformational changes in rpoB to perturb RIF binding. In principle, the approach combined fundamental molecular modeling tools for robust "global" and "local" level analyses of structural dynamics, making it well suited for investigating other similar drug resistance cases.

Molecular Evidence of Drug-Resistant Tuberculosis in the Balimo Region of Papua New Guinea

Papua New Guinea (PNG) has a high burden of tuberculosis (TB), including drug-resistant TB (DR-TB). DR-TB has been identified in patients in Western Province, although there has been limited study outside the provincial capital of Daru. This study focuses on the Balimo region of Western Province, aiming to identify the proportion of DR-TB, and characterise Mycobacterium tuberculosis (MTB) drug resistance-associated gene mutations. Sputum samples were investigated for MTB infection using published molecular methods. DNA from MTB-positive samples was amplified and sequenced, targeting the rpoB and katG genes to identify mutations associated with rifampicin and isoniazid resistance respectively. A total of 240 sputum samples were collected at Balimo District Hospital (BDH). Of these, 86 were classified as positive based on the results of the molecular assays. For samples where rpoB sequencing was successful, 10.0% (5/50, 95% CI 4.4–21.4%) were considered rifampicin-resistant through detection of drug resistance-associated mutations. We have identified high rates of presumptive DR-TB in the Balimo region of Western Province, PNG. These results emphasise the importance of further surveillance, and strengthening of diagnostic and treatment services at BDH and throughout Western Province, to facilitate detection and treatment of DR-TB, and limit transmission in this setting.

Genetic diversity of multidrug-resistant Mycobacterium tuberculosis strains isolated from tuberculosis patients in Iran using MIRU-VNTR technique

Tuberculosis (TB) is considered as one of the most important infectious diseases in the world, and recent rise and spread of multidrug-resistant (MDR) Mycobacterium tuberculosis (MTB) strains, have made the matter worsened. Due to the importance of TB prevalence in Iran, this study was designed to investigate the genetic diversity among MDR strains of MTB by MIRU-VNTR typing scheme. A total of 88 drug resistant M. tuberculosis isolates belong to pulmonary TB cases were collected from several TB reference centers of Iran. Drug susceptibility testing for Isoniazid and Rifampin was performed using the agar proportion method and MDR isolates were underwent genotyping by using 12-locus- based MIRU-VNTR typing. On performing proportion method, 22 isolates were identified as MDR. By typing of MDR isolates using 12-loci MIRU-VNTR technique, high diversity were demonstrated in MDR strains and these were classified into 20 distinct MIRU-VNTR genotypes. MIRU loci 10 and 26 were the most discriminatory loci with 8 and 7 alleles respectively; while MIRU loci 2, 20, 24 and 39 were found to be the least discriminatory with 1-2 alleles each. We noticed a mixed infection in isolate 53, as this isolate comprised simultaneous two alleles in MIRU loci 40, 10, 16 and 39. In conclusion, this result represents MIRU-VNTR typing as a useful tool for studying genetic diversity of MDR-MTB in regional settings, and will help the health sectors to construct a preventive program for MDR-TB. Additionally, it can detect mixed infection which can facilitate management of treatment.

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

INTRODUCTION

Tuberculosis remains the leading causes of death worldwide with frequencies of mutations in rifampicin and isoniazid resistant Mycobacterium tuberculosis isolates varying according to geographical location. There is limited information in Zimbabwe on specific antibiotic resistance gene mutation patterns in MTB and hence, increased rate of discordant results and mortality due to inappropriate antibiotic prescriptions. The rpoB and katG genes molecular markers are used for detecting rifampicin and isoniazid resistance respectively. Some mutations within these gene sequences are associated with drug resistance as they directly alter gene function. The objectives of this research was to determine the drug resistance profiles in M. tuberculosis isolates that are phenotypically resistant but not detected by the GeneXpert and MTBDRplus kit and also to detect mutations in the rpoB and katG genes which are not detected by the Hain Genotype MTBDRplus kit and GeneXpert diagnosis.

METHODS

PCR was used for the amplification of the rpoB and katG genes from MTB isolates collected from human clinical samples between 2008 and 2015. The genes were sequenced and compared to the wild type MTB H37Rv rpoB (accession number L27989) and kat G genes (KP46920), respectively. Sequence analysis results were compared to genotyping results obtained from molecular assays and culture results of all isolates.

RESULTS

The most frequent mutation responsible for rifampicin resistance was (25/92) S531L that was detected by using all molecular assays. Some inconsistencies were observed between phenotypic and genotypic assay results for both katG and rpoB genes in 30 strains. For these, eight codons; G507S, T508A, L511V, del513-526, P520P, L524L, R528H, R529Q and S531F were novel mutations. In addition, the I572P/F, E562Q, P564S, and Q490Y mutations were identified as novel mutations outside the rifampicin resistance determining region. In katG gene, amino acid changes to threonine, asparagine and isoleucine exhibited high degrees of polymorphism such as V473N, D311N, and L427I. The R463L (20/92) amino acid substitution was most common but was not associated with isoniazid resistance.

CONCLUSION

These finding indicate that molecular assay kit diagnosis that is based on the rpoB and katG genes should be improved to cater for the genetic variations associated with the geographic specificity of the target genes and be able to detect most prevalent mutations in different areas.