1
|
Hermans LE, Booysen P, Boloko L, Adriaanse M, de Wet TJ, Lifson AR, Wadee N, Papavarnavas N, Marais G, Hsiao NY, Rosslee MJ, Symons G, Calligaro GL, Iranzadeh A, Wilkinson RJ, Ntusi NA, Williamson C, Davies MA, Meintjes G, Wasserman S. Changing character and waning impact of COVID-19 at a tertiary centre in Cape Town, South Africa. S Afr J Infect Dis 2023; 38:550. [PMID: 38223432 PMCID: PMC10784273 DOI: 10.4102/sajid.v38i1.550] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2023] [Accepted: 10/27/2023] [Indexed: 01/16/2024] Open
Abstract
Background The emergence of genetic variants of SARS-CoV-2 was associated with changing epidemiological characteristics throughout coronavirus disease 2019 (COVID-19) pandemic in population-based studies. Individual-level data on the clinical characteristics of infection with different SARS-CoV-2 variants in African countries is less well documented. Objectives To describe the evolving clinical differences observed with the various SARS-CoV-2 variants of concern and compare the Omicron-driven wave in infections to the previous Delta-driven wave. Method We performed a retrospective observational cohort study among patients admitted to a South African referral hospital with COVID-19 pneumonia. Patients were stratified by epidemiological wave period, and in a subset, the variants associated with each wave were confirmed by genomic sequencing. Outcomes were analysed by Cox proportional hazard models. Results We included 1689 patients were included, representing infection waves driven predominantly by ancestral, Beta, Delta and Omicron BA1/BA2 & BA4/BA5 variants. Crude 28-day mortality was 25.8% (34/133) in the Omicron wave period versus 37.1% (138/374) in the Delta wave period (hazard ratio [HR] 0.68 [95% CI 0.47-1.00] p = 0.049); this effect persisted after adjustment for age, gender, HIV status and presence of cardiovascular disease (adjusted HR [aHR] 0.43 [95% CI 0.28-0.67] p < 0.001). Hospital-wide SARS-CoV-2 admissions and deaths were highest during the Delta wave period, with a decoupling of SARS-CoV-2 deaths and overall deaths thereafter. Conclusion There was lower in-hospital mortality during Omicron-driven waves compared with the prior Delta wave, despite patients admitted during the Omicron wave being at higher risk. Contribution This study summarises clinical characteristics associated with SARS-CoV-2 variants during the COVID-19 pandemic at a South African tertiary hospital, demonstrating a waning impact of COVID-19 on healthcare services over time despite epidemic waves driven by new variants. Findings suggest the absence of increasing virulence from later variants and protection from population and individual-level immunity.
Collapse
Affiliation(s)
- Lucas E. Hermans
- Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Petro Booysen
- Centre for Infectious Diseases Research in Africa, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - Linda Boloko
- Centre for Infectious Diseases Research in Africa, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - Marguerite Adriaanse
- Division of Infectious Diseases and HIV Medicine, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - Timothy J. de Wet
- Department of Medical Microbiology, Faculty of Health Sciences, University of Cape town, Cape Town, South Africa
| | - Aimee R. Lifson
- Department of Medicine, Faculty of Internal Medicine, Groote Schuur Hospital, Cape Town, South Africa
| | - Naweed Wadee
- Centre for Infectious Diseases Research in Africa, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - Nectarios Papavarnavas
- Institute of Infectious Disease and HIV Medicine, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - Gert Marais
- Division of Medical Virology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
- Division of Medical Microbiology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Nei-yuan Hsiao
- Division of Medical Virology, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | | | - Gregory Symons
- Department of Medicine, Division of Pulmonology, Groote Schuur Hospital, Cape Town, South Africa
| | - Gregory L. Calligaro
- Department of Medicine, Division of Pulmonology, Groote Schuur Hospital, Cape Town, South Africa
| | - Arash Iranzadeh
- Department of Integrative Biomedical Sciences, Computational Biology Division, University of Cape Town, Cape Town, South Africa
| | - Robert J. Wilkinson
- Centre for Infectious Diseases Research in Africa, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
- The Francis Crick Institute, London, United Kingdom
- Department of Infectious Disease, Imperial College, London, United Kingdom
| | - Ntobeko A.B. Ntusi
- Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
- South African Medical Research Council, University of Cape Town Extramural Research Unit on the Intersection of Noncommunicable Diseases and Infectious Diseases, Cape Town, South Africa
| | - Carolyn Williamson
- Department of Pathology, IDM and CIDRI-Africa, Division of Medical Virology, University of Cape Town, Cape Town, South Africa
| | - Mary-Ann Davies
- Department of Health and Wellness, Western Cape Government, Cape Town, South Africa
- Centre for Infectious Disease Epidemiology and Research, School of Public Health, University of Cape Town, Cape Town, South Africa
| | - Graeme Meintjes
- Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
- Centre for Infectious Diseases Research in Africa, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
| | - Sean Wasserman
- Centre for Infectious Diseases Research in Africa, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa
- Institute for Infection and Immunity, St George’s, University of London, London, United Kingdom
| |
Collapse
|
2
|
Gessner S, Martin ZAM, Reiche MA, Santos JA, Dinkele R, Ramudzuli A, Dhar N, de Wet TJ, Anoosheh S, Lang DM, Aaron J, Chew TL, Herrmann J, Müller R, McKinney JD, Woodgate R, Mizrahi V, Venclovas Č, Lamers MH, Warner DF. Investigating the composition and recruitment of the mycobacterial ImuA'-ImuB-DnaE2 mutasome. eLife 2023; 12:e75628. [PMID: 37530405 PMCID: PMC10421592 DOI: 10.7554/elife.75628] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 08/01/2023] [Indexed: 08/03/2023] Open
Abstract
A DNA damage-inducible mutagenic gene cassette has been implicated in the emergence of drug resistance in Mycobacterium tuberculosis during anti-tuberculosis (TB) chemotherapy. However, the molecular composition and operation of the encoded 'mycobacterial mutasome' - minimally comprising DnaE2 polymerase and ImuA' and ImuB accessory proteins - remain elusive. Following exposure of mycobacteria to DNA damaging agents, we observe that DnaE2 and ImuB co-localize with the DNA polymerase III β subunit (β clamp) in distinct intracellular foci. Notably, genetic inactivation of the mutasome in an imuBAAAAGG mutant containing a disrupted β clamp-binding motif abolishes ImuB-β clamp focus formation, a phenotype recapitulated pharmacologically by treating bacilli with griselimycin and in biochemical assays in which this β clamp-binding antibiotic collapses pre-formed ImuB-β clamp complexes. These observations establish the essentiality of the ImuB-β clamp interaction for mutagenic DNA repair in mycobacteria, identifying the mutasome as target for adjunctive therapeutics designed to protect anti-TB drugs against emerging resistance.
Collapse
Affiliation(s)
- Sophia Gessner
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
| | - Zela Alexandria-Mae Martin
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Laboratory of Microbiology and Microsystems, School of Life Sciences, Swiss Federal Institute of Technology in Lausanne (EPFL)LausanneSwitzerland
| | - Michael A Reiche
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Advanced Imaging Center, Howard Hughes Medical InstituteAshburnUnited States
| | - Joana A Santos
- Department of Cell and Chemical Biology, Leiden University Medical CenterLeidenNetherlands
| | - Ryan Dinkele
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
| | - Atondaho Ramudzuli
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
| | - Neeraj Dhar
- Laboratory of Microbiology and Microsystems, School of Life Sciences, Swiss Federal Institute of Technology in Lausanne (EPFL)LausanneSwitzerland
| | - Timothy J de Wet
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Department of Integrative Biomedical Sciences, University of Cape TownCape TownSouth Africa
| | - Saber Anoosheh
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
| | - Dirk M Lang
- Confocal and Light Microscope Imaging Facility, Department of Human Biology, University of Cape TownCape TownSouth Africa
| | - Jesse Aaron
- Advanced Imaging Center, Howard Hughes Medical InstituteAshburnUnited States
| | - Teng-Leong Chew
- Advanced Imaging Center, Howard Hughes Medical InstituteAshburnUnited States
| | - Jennifer Herrmann
- Helmholtz Centre for Infection Research, Helmholtz Institute for Pharmaceutical Research SaarlandSaarbrückenGermany
- German Centre for Infection Research (DZIF), Partner Site Hannover-BraunschweigBraunschweigGermany
| | - Rolf Müller
- Helmholtz Centre for Infection Research, Helmholtz Institute for Pharmaceutical Research SaarlandSaarbrückenGermany
- German Centre for Infection Research (DZIF), Partner Site Hannover-BraunschweigBraunschweigGermany
| | - John D McKinney
- Laboratory of Microbiology and Microsystems, School of Life Sciences, Swiss Federal Institute of Technology in Lausanne (EPFL)LausanneSwitzerland
| | - Roger Woodgate
- Laboratory of Genomic Integrity, Eunice Kennedy Shriver National Institute of Child Health and Human DevelopmentBethesdaUnited States
| | - Valerie Mizrahi
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Wellcome Centre for Infectious Diseases Research in Africa, University of Cape TownCape TownSouth Africa
| | | | - Meindert H Lamers
- Department of Cell and Chemical Biology, Leiden University Medical CenterLeidenNetherlands
| | - Digby F Warner
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DSI/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Wellcome Centre for Infectious Diseases Research in Africa, University of Cape TownCape TownSouth Africa
| |
Collapse
|
3
|
Niemand Wolhuter N, Ngakane L, de Wet TJ, Warren RM, Williams MJ. The Mycobacterium smegmatis HesB Protein, MSMEG_4272, Is Required for In Vitro Growth and Iron Homeostasis. Microorganisms 2023; 11:1573. [PMID: 37375075 DOI: 10.3390/microorganisms11061573] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 06/07/2023] [Accepted: 06/09/2023] [Indexed: 06/29/2023] Open
Abstract
A-type carrier (ATC) proteins are proposed to function in the biogenesis of Fe-S clusters, although their exact role remains controversial. The genome of Mycobacterium smegmatis encodes a single ATC protein, MSMEG_4272, which belongs to the HesB/YadR/YfhF family of proteins. Attempts to generate an MSMEG_4272 deletion mutant by two-step allelic exchange were unsuccessful, suggesting that the gene is essential for in vitro growth. CRISPRi-mediated transcriptional knock-down of MSMEG_4272 resulted in a growth defect under standard culture conditions, which was exacerbated in mineral-defined media. The knockdown strain displayed reduced intracellular iron levels under iron-replete conditions and increased susceptibility to clofazimine, 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), and isoniazid, while the activity of the Fe-S containing enzymes, succinate dehydrogenase, and aconitase were not affected. This study suggests that MSMEG_4272 plays a role in the regulation of intracellular iron levels and is required for in vitro growth of M. smegmatis, particularly during exponential growth.
Collapse
Affiliation(s)
- Nandi Niemand Wolhuter
- NRF/DSI Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town 7505, South Africa
| | - Lerato Ngakane
- NRF/DSI Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town 7505, South Africa
| | - Timothy J de Wet
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology, University of Cape Town, Cape Town 7925, South Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town 7925, South Africa
| | - Robin M Warren
- NRF/DSI Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town 7505, South Africa
| | - Monique J Williams
- NRF/DSI Centre of Excellence for Biomedical Tuberculosis Research, South African Medical Research Council Centre for Tuberculosis Research, Division of Molecular Biology and Human Genetics, Faculty of Medicine and Health Sciences, Stellenbosch University, Cape Town 7505, South Africa
- Department of Molecular and Cell Biology, University of Cape Town, Cape Town 7700, South Africa
| |
Collapse
|
4
|
Barr DA, Schutz C, Balfour A, Shey M, Kamariza M, Bertozzi CR, de Wet TJ, Dinkele R, Ward A, Haigh KA, Kanyik JP, Mizrahi V, Nicol MP, Wilkinson RJ, Lalloo DG, Warner DF, Meintjes G, Davies G. Serial measurement of M. tuberculosis in blood from critically-ill patients with HIV-associated tuberculosis. EBioMedicine 2022; 78:103949. [PMID: 35325781 PMCID: PMC8938880 DOI: 10.1016/j.ebiom.2022.103949] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2021] [Revised: 02/16/2022] [Accepted: 03/04/2022] [Indexed: 11/25/2022] Open
|
5
|
Tanner L, Mashabela GT, Omollo CC, de Wet TJ, Parkinson CJ, Warner DF, Haynes RK, Wiesner L. Intracellular Accumulation of Novel and Clinically Used TB Drugs Potentiates Intracellular Synergy. Microbiol Spectr 2021; 9:e0043421. [PMID: 34585951 PMCID: PMC8557888 DOI: 10.1128/spectrum.00434-21] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2021] [Accepted: 08/19/2021] [Indexed: 12/13/2022] Open
Abstract
The therapeutic repertoire for tuberculosis (TB) remains limited despite the existence of many TB drugs that are highly active in in vitro models and possess clinical utility. Underlying the lack of efficacy in vivo is the inability of TB drugs to penetrate microenvironments inhabited by the causative agent, Mycobacterium tuberculosis, including host alveolar macrophages. Here, we determined the ability of the phenoxazine PhX1 previously shown to be active against M. tuberculosis in vitro to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. We also investigated the extent of permeation into uninfected and M. tuberculosis-infected human macrophage-like Tamm-Horsfall protein 1 (THP-1) cells directly and by comparing to results obtained in vitro in synergy assays. Our data indicate that PhX1 (4,750 ± 127.2 ng/ml) penetrates more effectively into THP-1 cells than do the clinically used anti-TB agents, rifampin (3,050 ± 62.9 ng/ml), moxifloxacin (3,374 ± 48.7 ng/ml), bedaquiline (4,410 ± 190.9 ng/ml), and linezolid (770 ± 14.1 ng/ml). Compound efficacy in infected cells correlated with intracellular accumulation, reinforcing the perceived importance of intracellular penetration as a key drug property. Moreover, we detected synergies deriving from redox-stimulatory combinations of PhX1 or clofazimine with the novel prenylated amino-artemisinin WHN296. Finally, we used compound synergies to elucidate the relationship between compound intracellular accumulation and efficacy, with PhX1/WHN296 synergy levels shown to predict drug efficacy. Collectively, our data support the utility of the applied assays in identifying in vitro active compounds with the potential for clinical development. IMPORTANCE This study addresses the development of novel therapeutic compounds for the eventual treatment of drug-resistant tuberculosis. Tuberculosis continues to progress, with cases of Mycobacterium tuberculosis (M. tuberculosis) resistance to first-line medications increasing. We assess new combinations of drugs with both oxidant and redox properties coupled with a third partner drug, with the focus here being on the potentiation of M. tuberculosis-active combinations of compounds in the intracellular macrophage environment. Thus, we determined the ability of the phenoxazine PhX1, previously shown to be active against M. tuberculosis in vitro, to differentially penetrate murine compartments, including plasma, epithelial lining fluid, and isolated epithelial lining fluid cells. In addition, the extent of permeation into human macrophage-like THP-1 cells and H37Rv-infected THP-1 cells was measured via mass spectrometry and compared to in vitro two-dimensional synergy and subsequent intracellular efficacy. Collectively, our data indicate that development of new drugs will be facilitated using the methods described herein.
Collapse
Affiliation(s)
- Lloyd Tanner
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| | - Gabriel T. Mashabela
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Charles C. Omollo
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | - Timothy J. de Wet
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
| | | | - Digby F. Warner
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa
- Wellcome Centre for Infectious Diseases Research in Africa, University of Cape Town, Cape Town, South Africa
| | - Richard K. Haynes
- Centre of Excellence for Pharmaceutical Sciences, Faculty of Health Sciences, North-West University, Potchefstroom, South Africa
| | - Lubbe Wiesner
- Division of Clinical Pharmacology, Department of Medicine, University of Cape Town, Cape Town, South Africa
| |
Collapse
|
6
|
de Wet TJ, Winkler KR, Mhlanga M, Mizrahi V, Warner DF. Arrayed CRISPRi and quantitative imaging describe the morphotypic landscape of essential mycobacterial genes. eLife 2020; 9:e60083. [PMID: 33155979 PMCID: PMC7647400 DOI: 10.7554/elife.60083] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 10/03/2020] [Indexed: 12/11/2022] Open
Abstract
Mycobacterium tuberculosis possesses a large number of genes of unknown or predicted function, undermining fundamental understanding of pathogenicity and drug susceptibility. To address this challenge, we developed a high-throughput functional genomics approach combining inducible CRISPR-interference and image-based analyses of morphological features and sub-cellular chromosomal localizations in the related non-pathogen, M. smegmatis. Applying automated imaging and analysis to 263 essential gene knockdown mutants in an arrayed library, we derive robust, quantitative descriptions of bacillary morphologies consequent on gene silencing. Leveraging statistical-learning, we demonstrate that functionally related genes cluster by morphotypic similarity and that this information can be used to inform investigations of gene function. Exploiting this observation, we infer the existence of a mycobacterial restriction-modification system, and identify filamentation as a defining mycobacterial response to histidine starvation. Our results support the application of large-scale image-based analyses for mycobacterial functional genomics, simultaneously establishing the utility of this approach for drug mechanism-of-action studies.
Collapse
Affiliation(s)
- Timothy J de Wet
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
| | - Kristy R Winkler
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
| | - Musa Mhlanga
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Department of Integrative Biomedical Sciences, University of Cape TownCape TownSouth Africa
| | - Valerie Mizrahi
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Wellcome Centre for Infectious Diseases Research in Africa, University of Cape TownCape TownSouth Africa
| | - Digby F Warner
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit, Department of Pathology, University of Cape TownCape TownSouth Africa
- Institute of Infectious Disease and Molecular Medicine, University of Cape TownCape TownSouth Africa
- Wellcome Centre for Infectious Diseases Research in Africa, University of Cape TownCape TownSouth Africa
| |
Collapse
|
7
|
Abstract
Tuberculosis (TB) is the leading cause of mortality globally resulting from an infectious disease, killing almost 1.6 million people annually and accounting for approximately 30% of deaths attributed to antimicrobial resistance (AMR). This despite the widespread administration of a neonatal vaccine, and the availability of an effective combination drug therapy against the causative agent, Mycobacterium tuberculosis (Mtb). Instead, TB prevalence worldwide is characterized by high-burden regions in which co-epidemics, such as HIV, and social and economic factors, undermine efforts to control TB. These elements additionally ensure conditions that favor the emergence of drug-resistant Mtb strains, which further threaten prospects for future TB control. To address this challenge, significant resources have been invested in developing a TB drug pipeline, an initiative given impetus by the recent regulatory approval of two new anti-TB drugs. However, both drugs have been reserved for drug-resistant disease, and the seeming inevitability of new resistance plus the recognized need to shorten the duration of chemotherapy demands continual replenishment of the pipeline with high-quality "hits" with novel mechanisms of action. This represents a massive challenge, which has been undermined by key gaps in our understanding of Mtb physiology and metabolism, especially during host infection. Whereas drug discovery for other bacterial infections can rely on predictive in vitro assays and animal models, for Mtb, inherent metabolic flexibility and uncertainties about the nutrients available to infecting bacilli in different host (micro)environments instead requires educated predictions or demonstrations of efficacy in animal models of arguable relevance to human disease. Even microbiological methods for enumeration of viable mycobacterial cells are fraught with complication. Our research has focused on elucidating those aspects of mycobacterial metabolism that contribute to the robustness of the bacillus to host immunological defenses and applied antibiotics and that, possibly, drive the emergence of drug resistance. This work has identified a handful of metabolic pathways that appear vulnerable to antibiotic targeting. Those highlighted, here, include the inter-related functions of pantothenate and coenzyme A biosynthesis and recycling and nucleotide metabolism-the last of which reinforces our view that DNA metabolism constitutes an under-explored area for new TB drug development. Although nonessential functions have traditionally been deprioritized for antibiotic development, a common theme emerging from this work is that these very functions might represent attractive targets because of the potential to cripple mechanisms critical to bacillary survival under stress (for example, the RelMtb-dependent stringent response) or to adaptability under unfavorable, potentially lethal, conditions including antibiotic therapy (for example, DnaE2-dependent SOS mutagenesis). The bar, however, is high: demonstrating convincingly the likely efficacy of this strategy will require innovative models of human TB disease. In the concluding section, we focus on the need for improved techniques to elucidate mycobacterial metabolism during infection and its impact on disease outcomes. Here, we argue that developments in other fields suggest the potential to break through this barrier by harnessing chemical-biology approaches in tandem with the most advanced technologies. As researchers based in a high-burden country, we are impelled to continue participating in this important endeavor.
Collapse
Affiliation(s)
- Timothy J. de Wet
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit and DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory, Cape Town 7925, South Africa
- Department of Integrative Biomedical Sciences, University of Cape Town, Observatory, Cape Town 7925, South Africa
| | - Digby F. Warner
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit and DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory, Cape Town 7925, South Africa
- Wellcome Centre for Infectious Disease Research in Africa, University of Cape Town, Observatory, Cape Town 7925, South Africa
| | - Valerie Mizrahi
- SAMRC/NHLS/UCT Molecular Mycobacteriology Research Unit and DST/NRF Centre of Excellence for Biomedical TB Research, Department of Pathology and Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Observatory, Cape Town 7925, South Africa
- Wellcome Centre for Infectious Disease Research in Africa, University of Cape Town, Observatory, Cape Town 7925, South Africa
| |
Collapse
|