Genetic diversity of Mycobacterium leprae: Need to move towards genome-wide approaches.

ABSTRACT: Leprosy, an ancient disease, continues to be a public health concern as it remains endemic in several countries. After reaching the elimination target (1/10,000) as a public health problem in 2005 in India, around 1.2 lakh cases have been detected every year over the last decade indicating active transmission of leprosy bacillus (Mycobacterium leprae). Single-nucleotide polymorphisms (SNPs), genomic insertions/deletions and variable-number tandem repeats (VNTRs) have been identified as genetic markers for tracking M. leprae transmission. As the leprosy bacilli cannot be cultured in vitro, molecular testing of M. leprae genotypes is done by polymerase chain reaction-based sequencing which provides a practical alternative for the identification of strains as well as drug resistance-associated mutations. Whole-genome sequencing (WGS) of M. leprae directly from clinical samples has also proven to be an effective tool for identifying genetic variations which can further help refine the molecular epidemiological schemes based on SNPs and VNTRs. However, the WGS data of M. leprae strains from India are scarce, being responsible for a gross under-representation of the genetic diversity of M. leprae strains present in India and need to be addressed suitably. Molecular studies of leprosy can provide better insight into phylogeographic markers to monitor the transmission dynamics and emergence of antimicrobial resistance. An improved understanding of M. leprae transmission is essential to guide efficient leprosy control strategies. Therefore, this review compiles and discusses the current status of molecular epidemiology, genotyping and the potential of genome-wide analysis of M. leprae strains in the Indian context.

Novel mutations found in Mycobacterium leprae DNA repair gene nth from central India.

INTRODUCTION: The importance of DNA repair enzymes in maintaining genomic integrity is highlighted by the hypothesis that DNA damage by reactive oxygen/nitrogen species produced inside the host cell is essential for the mutagenesis process. Endonuclease III (Nth), formamidopyrimide (Fpg) and endonuclease VIII (Nei) DNA glycosylases are essential components of the bacterial base excision repair process. Mycobacterium leprae lost both fpg/nei genes during the reductive evolution event and only has the nth (ML2301) gene. This study aims to characterize the mutations in the nth gene of M. leprae strains and explore its correlation with drug-resistance. METHOD: A total of 91 M. leprae positive DNA samples extracted from skin biopsy samples of newly diagnosed leprosy patients from NSCB Hospital Jabalpur were assessed for the nth gene as well as drug resistance-associated loci of the rpoB, gyrA and folP1 genes through PCR followed by Sanger sequencing. RESULTS: Of these 91 patients, a total of two insertion frameshift mutations, two synonymous and seven nonsynonymous mutations were found in nth in seven samples. Sixteen samples were found to be resistant to ofloxacin and one was found to be dapsone resistant as per the known DRDR mutations. No mutations were found in the rpoB region. Interestingly, none of the nth mutations were identified in the drug-resistant associated samples. CONCLUSION: The in-silico structural analysis of the non-synonymous mutations in the Nth predicted five of them were to be deleterious. Our results suggest that the mutations in the nth gene may be potential markers for phylogenetic and epidemiological studies.

Multiplex PCR-based RFLP assay for early identification of prevalent Mycobacterium leprae genotypes.

Mycobacterium leprae is classified into four SNP genotypes and 16 subtypes (from 1A to 4P) that exhibit phylogeographical association reported from around the world. Among them, genotypes 1D and 3I represent more than 60% of M. leprae strains. Here, we report a new method for M. leprae genotyping which identifies the genotypes 1D and 3I by combining multiplex PCR amplification and restriction fragment length polymorphism (RFLP) of a M. leprae DNA amplicons using AgeI restriction enzyme. Agarose gel electrophoresis showed a deletion of 11 bp only among 3I genotypes by electrophoresis. When this multiplex PCR reaction is subjected to AgeI digestion, successful restriction digestion shows three bands for all the genotypes except 1D where only two bands were observed due to loss of restriction site. This method gives us the advantage of 1-step identification of the two most prevalent strains of M. leprae without using specialized equipments such as the Sanger sequencing system or quantitative PCR.

Interaction of surface glycoprotein of SARS-CoV-2 variants of concern with potential drug candidates: A molecular docking study.

Background: COVID-19 has become a global threat. Since its first outbreak from Wuhan, China in December 2019, the SARS-CoV-2 virus has gone through structural changes arising due to mutations in its surface glycoprotein. These mutations have led to the emergence of different genetic variants threatening public health due to increased transmission and virulence. As new drug development is a long process, repurposing existing antiviral drugs with potential activity against SARS-CoV-2 might be a possible solution to mitigate the current situation. Methods: This study focused on utilizing molecular docking to determine the effect of potential drugs on several variants of concern (VOCs). The effect of various drugs such as baricitinib, favipiravir, lopinavir, remdesivir and dexamethasone, which might have the potential to treat SARS-CoV-2 infections as evident from previous studies, was investigated for different VOCs. Results: Remdesivir showed promising results for B.1.351 variant (binding energy: -7.3 kcal/mol) with residues Gln319 and Val503 facilitating strong binding. Favipiravir showed favorable results against B.1.1.7 (binding energy: -5.6 kcal/mol), B.1.351 (binding energy: -5.1 kcal/mol) and B.1.617.2 (binding energy: -5 kcal/mol). Molecular dynamics simulation for favipiravir/B.1.1.7 was conducted and showed significant results in agreement with our findings. Conclusions: From structural modeling and molecular docking experiments, it is evident that mutations outside the receptor binding domain of surface glycoprotein do not have a sharp impact on drug binding affinity. Thus, the potential use of these drugs should be explored further for their antiviral effect against SARS-CoV-2 VOCs.

Simultaneous detection and differentiation between Mycobacterium leprae and Mycobacterium lepromatosis using novel polymerase chain reaction primers.

We have developed a polymerase chain reaction-based method to detect and distinguish Mycobacterium leprae and Mycobacterium lepromatosis using a single set of primers based on a 45-bp difference in the amplicon size of their rpoT gene. This method can also help in detecting the cases of co-infection in a single experiment.

Mycobacterium lepromatosis MLPM_5000 is a potential heme chaperone protein HemW and mis-annotation of its orthologues in mycobacteria.

The genome of a newly identified leprosy causing bacillus Mycobacterium lepromatosis was sequenced in 2015 wherein a gene MLPM_5000 was detected whose corresponding sequences are missing in its close relative Mycobacterium leprae, the well-known causal agent of leprosy. Thus MLPM_5000 is considered to be a specific genomic locus for differentiating M. lepromatosis from M. leprae. The locus was annotated as HemN (Coproporphyrinogen III oxidase) based on the available annotations in other mycobacterial species. However, we noticed that the MLPM_5000 and its orthologues in different mycobacterial species show a much higher degree of similarity with Escherichia coli HemW (378 aa) in comparison to the E. coli HemN (457 aa). Additionally, the fourth cysteine of the characteristic CX3CX2CXC motif of the E. coli HemN is replaced by a phenylalanine in the M. lepromatosis MLPM_5000 and its mycobacterial orthologues, which is a hallmark of heme chaperone protein HemW in E. coli and other species. Phylogenetic analysis of MLPM_5000 and its mycobacterial orthologues also showed that these proteins form a divergent phylogenetic clade with the HemW proteins of other species such as Escherichia coli and Lactococcus lactis. Further, Molecular Dynamics simulation studies also predicted that the residues of conserved HNXXYW motif of the MLPM_5000 may have a role in binding to heme part of the host hemoglobin, thereby suggesting it to be a HemW instead of HemN. Altogether, this work shows that MLPM_5000 and its mycobacterial orthologues are highly unlikely to be HemN. Therefore, the current annotations of mycobacterial HemN sequences should be corrected to heme chaperone 'HemW' in various protein databases. The study not only corrects the mis-annotation but also provides a new perspective in the context of evolutionary history of M. leprae and M. lepromatosis such as lack of HemW in M. leprae may explain some of the variations in the virulence between the two pathogens.