Doctoral Degrees (Molecular Biology and Human Genetics)

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Browsing Doctoral Degrees (Molecular Biology and Human Genetics) by browse.metadata.advisor "Baker, Bienyameen"

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    2020-12-11 Global transcriptomic investigation of the human macrophage response towards pathogenic/non-pathogenic mycobacteria
    (Stellenbosch : Stellenbosch University, 2019-12) Mishra, Abhilasha Madhvi; Baker, Bienyameen; Leisching, Gina; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Molecular Biology and Human Genetics
    Background:Tuberculosis (TB) is a major cause of infection-related mortalityworldwide. In 2017 an estimated 1.3 million people who were HIV-negative died of TB. An estimated 5-10% of infected individual develop active TB during their lifetime, while the remaining90% (of infected population) successfully control the bacteria. Also, some of the close household contacts of TB patients remain uninfected and healthy. Studying host immune response towards Mycobacterium tuberculosis(M. tb) can unfold the reason behind this enigma. Methods:We conducted a detailed investigation of in vitrohost response from human monocyte derived macrophages(hMDMs)towards different strains of mycobacteria(grown in detergent-freemedia), i.e. pathogenic (M. tbR179) andnon-pathogenic (M. smegmatisand M. bovisBCG). The host response was measured post-infection (at mRNA and protein levels) using AmpliSeq, quantitative real time polymerase chain reaction (qRT-PCR), multiplex ELISA (Luminex), intracellular mycobacterial survivaland cytotoxicity assay. Biological network analysis (ingenuity pathway analysis IPA) was performed to understand the gene regulatory networkinvolved in the pathophysiology associated with the host-immune system.Based on false discovery rate (FDR) and biological functions, we selected an inter-related gene family of interferon induced protein with tetratricopeptides (IFIT1, IFIT2 andIFIT3) from the list of 19 potential differentially expressed genes(DEGs)for knock-up (vector-based over-expression)/down experiments. This gene family is known to form a protein complex during viral infection to act against the antigen. Studyencompassing their role against bacteria is not well established.Therefore, we performed knocking-up of IFITsvia vector-based transfection and knocking-down via small interferingRNA (siRNA) approach to investigate their effect upon mycobacteria inside the host macrophages. Results:AmpliSeqanalysis found 19 DEGs at 12 hours post-infection across all three strains. We observed lower number of mycobacterial CFUs and higher host response (at both RNA and protein level) in hMDMs infected with M. smegmatisas compared to other two strains. Biological network analysis revealed interferon-interleukin associated signalling pathways as most prominent among the 19 differentially expressed genes.We found a differed host response towardsall three strains, which mayattributeto their pathogenicity. Messenger RNA and protein level comparisons at different time points, depicted strong role of interferon and interleukin associated gene network. This network was able to successfully counter M. smegmatisbut succumb to M. bovisBCG andM. tbR179. Most importantly, across all three strains, intra-cellular bacterial growth and survival measured through colony forming units (CFUs)decreased significantly upon knocking up of IFITs(IFIT1, IFIT2 andIFIT3),while we recordedan increase in CFUs upon knocking down ofIFITsin the host macrophages. Using multiplex ELISA, we found higher expression of key pro-inflammatory cytokines (i.e. IDO1, IFN-γ, IL-6, and IL-23) during knock-up (vector-based over-expression)of IFITsresulting in reduction of mycobacteria. Conclusion:Differentially expressed IFITs showed a strong effect against mycobacteria, which can be used as a promising therapeutic targetadjunct to anti-TB therapy. This knowledge will broaden the scope of host drug targets for resistance free bacteriostatic immuno-therapy.
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    Investigation of the activity of sulfonamide anti-bacterial drugs in Mycobacterium tuberculosis and the role of oxidative stress on the efficacy of these drugs
    (Stellenbosch : Stellenbosch University, 2014-04) Macingwana, Lubabalo; Wiid, Ian J. F.; Baker, Bienyameen; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences, Molecular Biology and Human Genetics.
    ENGLISH ABSTRACT: Tuberculosis (TB) has become a global health epidemic affecting millions of people worldwide with a high incidence in third-world countries. The emergence of multi-drug and extremely-drug resistant M. tuberculosis strains together with the HIV/AIDS pandemic warrants the need for new drugs or new drug combinations. The folic acid synthesis pathway is one of the key pathways that are essential for the survival of bacteria in general. Sulfonamides are a group of compounds that target folic acid synthesis, particularly dihydropteroate synthetase, the first enzyme in the folate pathway. Some of these sulfonamides were used during the introduction of chemotherapy for the treatment of TB in the 1930s, but had toxic side effects. Newer derivatives became safer, but were not employed again for TB treatment. In a recent case study it was reported that the combination of trimethoprim-sulfamethoxazole (Bactrim), which is used to treat various bacterial infections, such as urinary tract infections, had activity against M. tuberculosis. In light of this and the fact that trimethoprim-sulfamethoxazole is well tolerated by humans, we have investigated their antimycobacterial activity with particular interest in the combinational effect of sulfamethoxazole and trimethoprim with the first-line anti-TB drugs, Isoniazid, Rifampicin and Ethambutol against M. tuberculosis. Since sulfonamides are known to produce oxidative stress, we also investigated the contribution of this factor to the efficacy of sulfamethoxazole using a mycothiol deficient strain of M. tuberculosis, ΔmshA. Though trimethoprim-sulfamethoxazole targets the folic acid pathway, we also investigated the possibility that trimethoprim-sulfamethoxazole may have other cellular targets and applied proteomic analysis. We have found that Trimethoprim-Sulfamethoxazole has activity against M. tuberculosis and that Sulfamethoxazole is the active compound. However, our observation was that not all sulfonamides are active against M. tuberculosis. In addition we observed that sulfamethoxazole enhances the activity of Rifampicin against M. tuberculosis in a synergistic way. We also observed that a mycothiol deletion mutant was more susceptible to Sulfamethoxazole compared to the wild type strain CDC 1551. Through global protein expression profiling (Proteomics) we were also able to show that sulfamethoxazole could also kill M. tuberculosis by oxidative stress production as we identified oxidative stress responsive proteins that were differentially regulated upon exposure to sulfamethoxazole. As trimethoprim-sulfamethoxazole is a registered drug combination, inexpensive and widely available, we propose that this regimen could be used in our fight against M. tuberculosis infection.
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    The role of ergothioneine in mycobacteria
    (Stellenbosch : Stellenbosch University, 2015-12) Sao Emani, Carine; Baker, Bienyameen; Williams, Monique Joy; Wiid, Ian Johannes; Stellenbosch University. Faculty of Medicine and Health Sciences. Dept. of Biomedical Sciences: Molecular Biology and Human Genetics