38 results on '"Frederick A. Sirgel"'
Search Results
2. Emergence and Spread of Extensively and Totally Drug-Resistant Tuberculosis, South Africa
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Marisa Klopper, Robin Mark Warren, Cindy Hayes, Nicolaas Claudius Gey van Pittius, Elizabeth Maria Streicher, Borna Müller, Frederick Adriaan Sirgel, Mamisa Chabula-Nxiweni, Ebrahim Hoosain, Gerrit Coetzee, Paul David van Helden, Thomas Calldo Victor, and André Phillip Trollip
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Tuberculosis ,multidrug-resistant tuberculosis ,MDR-TB ,extensively drug-resistant tuberculosis ,XDR-TB ,totally drug-resistant tuberculosis ,Medicine ,Infectious and parasitic diseases ,RC109-216 - Abstract
Factors driving the increase in drug-resistant tuberculosis (TB) in the Eastern Cape Province, South Africa, are not understood. A convenience sample of 309 drug-susceptible and 342 multidrug-resistant (MDR) TB isolates, collected July 2008–July 2009, were characterized by spoligotyping, DNA fingerprinting, insertion site mapping, and targeted DNA sequencing. Analysis of molecular-based data showed diverse genetic backgrounds among drug-sensitive and MDR TB sensu stricto isolates in contrast to restricted genetic backgrounds among pre–extensively drug-resistant (pre-XDR) TB and XDR TB isolates. Second-line drug resistance was significantly associated with the atypical Beijing genotype. DNA fingerprinting and sequencing demonstrated that the pre-XDR and XDR atypical Beijing isolates evolved from a common progenitor; 85% and 92%, respectively, were clustered, indicating transmission. Ninety-three percent of atypical XDR Beijing isolates had mutations that confer resistance to 10 anti-TB drugs, and some isolates also were resistant to para-aminosalicylic acid. These findings suggest the emergence of totally drug-resistant TB.
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- 2013
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3. Linezolid Population Pharmacokinetics in South African Adults with Drug-Resistant Tuberculosis
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Gary Maartens, Keertan Dheda, Lubbe Wiesner, Frederick A. Sirgel, Neel R. Gandhi, Sean Wasserman, James C.M. Brust, Graeme Meintjes, Mahmoud Tareq Abdelwahab, Paolo Denti, and Robin M. Warren
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Adult ,medicine.medical_specialty ,Antitubercular Agents ,Black People ,HIV Infections ,Clinical Therapeutics ,law.invention ,chemistry.chemical_compound ,Therapeutic index ,Pharmacokinetics ,Randomized controlled trial ,Interquartile range ,law ,Internal medicine ,Tuberculosis, Multidrug-Resistant ,Medicine ,Humans ,Pharmacology (medical) ,Dosing ,Adverse effect ,Pharmacology ,business.industry ,Linezolid ,NONMEM ,Infectious Diseases ,chemistry ,Female ,business - Abstract
Linezolid is widely used for drug-resistant tuberculosis (DR-TB) but has a narrow therapeutic index. To inform dose optimization, we aimed to characterize the population pharmacokinetics of linezolid in South African participants with DR-TB and explore the effect of covariates, including HIV coinfection, on drug exposure. Data were obtained from pharmacokinetic substudies in a randomized controlled trial and an observational cohort study, both of which enrolled adults with drug-resistant pulmonary tuberculosis. Participants underwent intensive and sparse plasma sampling. We analyzed linezolid concentration data using nonlinear mixed-effects modeling and performed simulations to estimate attainment of putative efficacy and toxicity targets. A total of 124 participants provided 444 plasma samples; 116 were on the standard daily dose of 600 mg, while 19 had dose reduction to 300 mg due to adverse events. Sixty-one participants were female, 71 were HIV-positive, and their median weight was 56 kg (interquartile range [IQR], 50 to 63). In the final model, typical values for clearance and central volume were 3.57 liters/h and 40.2 liters, respectively. HIV coinfection had no significant effect on linezolid exposure. Simulations showed that 600-mg dosing achieved the efficacy target (area under the concentration-time curve for the free, unbound fraction of the drug [[Formula: see text] at a MIC level of 0.5 mg/liter) with 96% probability but had 56% probability of exceeding safety target ([Formula: see text]. The 300-mg dose did not achieve adequate efficacy exposures. Our model characterized population pharmacokinetics of linezolid in South African patients with DR-TB and supports the 600-mg daily dose with safety monitoring.
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- 2021
4. 1,3-Diarylpyrazolyl-acylsulfonamides as Potent Anti-tuberculosis Agents Targeting Cell Wall Biosynthesis in
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Lutete Peguy, Khonde, Rudolf, Müller, Grant A, Boyle, Virsinha, Reddy, Aloysius T, Nchinda, Charles J, Eyermann, Stephen, Fienberg, Vinayak, Singh, Alissa, Myrick, Efrem, Abay, Mathew, Njoroge, Nina, Lawrence, Qin, Su, Timothy G, Myers, Helena I M, Boshoff, Clifton E, Barry, Frederick A, Sirgel, Paul D, van Helden, Lisa M, Massoudi, Gregory T, Robertson, Anne J, Lenaerts, Gregory S, Basarab, Sandeep R, Ghorpade, and Kelly, Chibale
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Models, Molecular ,Structure-Activity Relationship ,Sulfonamides ,Molecular Structure ,Cell Wall ,Drug Discovery ,Antitubercular Agents ,Humans ,Hep G2 Cells ,Microbial Sensitivity Tests ,Mycobacterium tuberculosis - Abstract
Phenotypic whole cell high-throughput screening of a ∼150,000 diverse set of compounds against
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- 2021
5. Correction: The Rationale for Using Rifabutin in the Treatment of MDR and XDR Tuberculosis Outbreaks.
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Frederick A Sirgel, Robin M Warren, Erik C Böttger, Marisa Klopper, Thomas C Victor, and Paul D van Helden
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Medicine ,Science - Published
- 2015
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6. Rifampicin mono-resistant tuberculosis is not the same as multidrug-resistant tuberculosis: a descriptive study from Khayelitsha, South Africa
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Sebastien Gagneux, Miriam Reinhard, Fabrizio Menardo, Helen Cox, Elizabeth M. Streicher, Mark P. Nicol, Anna Doetsch, Patrick G T Cudahy, Anzaan Dippenaar, Johnny Daniels, Zubeida Salaam-Dreyer, Robin M. Warren, Erika Mohr-Holland, Frederick A. Sirgel, and Sonia Borrell
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Mutation ,Tuberculosis ,business.industry ,Odds ratio ,Drug susceptibility ,rpoB ,medicine.disease ,medicine.disease_cause ,Virology ,Resistant tuberculosis ,Multiple drug resistance ,medicine ,business ,Rifampicin ,medicine.drug - Abstract
Rifampicin mono-resistant TB (RMR-TB) constitutes 38% of all rifampicin-resistant TB (RR-TB) in South Africa and is increasing. We aimed to compare RMR-TB with multidrug-resistant TB (MDR-TB) within a high TB, RR-TB and HIV burden setting. Patient-level clinical data and stored RR-TB isolates from 2008-2017 with available whole genome sequencing (WGS) data were used to describe risk factors associated with RMR-TB and to compare rifampicin-resistance (RR) conferring mutations between RMR-TB and MDR-TB. A subset of isolates with particular RR-conferring mutations were subjected to semi-quantitative rifampicin phenotypic drug susceptibility testing. Among 2,041 routinely diagnosed RR-TB patients, 463 (22.7%) had RMR-TB. HIV-positive individuals (adjusted Odds Ratio 1.4, 95% CI 1.1-1.9) and diagnosis between 2013-2017 versus 2008-2012 (aOR 1.3, 1.1-1.7) were associated with RMR-TB. Among 1,119 (54.8%) patients with available WGS data showing RR-TB, significant differences in the distribution of rpoB RR-conferring mutations between RMR-TB and MDR-TB isolates were observed. Mutations associated with high-level RR were more commonly found among MDR-TB isolates (811/889, 90.2% versus 162/230, 70.4% among RMR-TB, prpoB L430P mutation, conferring low-level RR, was identified in 32/230 (13.9%) RMR-TB versus 10/889 (1.1%) in MDR-TB (prpoB L430P mutation, 7 were phenotypically susceptible using the critical concentration of 0.5 µg/ml (range 0.125-1 µg/ml). The majority (215/230, 93.5%) of RMR-TB isolates showed susceptibility to all other TB drugs, highlighting the potential benefits of WGS for simplified treatment. These data suggest that the evolution of RMR-TB differs from MDR-TB with a potential contribution from HIV infection.
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- 2021
7. Minority Mycobacterium tuberculosis Genotypic Populations as an Indicator of Subsequent Phenotypic Resistance
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Frederick A. Sirgel, Eric Vittinghoff, Grant Theron, Elizabeth M. Streicher, Darrin Lemmer, David M. Engelthaler, Erin Kelley, Kristin Wiggins, John Z. Metcalfe, Robin M. Warren, Christopher J. Allender, and Dulce Jimenez
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Pulmonary and Respiratory Medicine ,Genetics ,Tuberculosis ,Extramural ,Clinical Biochemistry ,Cell Biology ,Drug resistance ,Biology ,medicine.disease ,biology.organism_classification ,Bacterial genetics ,Mycobacterium tuberculosis ,Genotype ,medicine ,Phenotypic resistance ,Molecular Biology ,Selection (genetic algorithm) - Published
- 2019
8. Drug-Penetration Gradients Associated with Acquired Drug Resistance in Patients with Tuberculosis
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Tawanda Gumbo, Shashikant Srivastava, Robin M. Warren, Edward K. Wakeland, Loven Moodley, Keertan Dheda, Timothy Pennel, Anthony Linegar, Frederick A. Sirgel, Laura Lenders, Gesham Magombedze, Jotam G. Pasipanodya, Erland Arning, Paul D. van Helden, Paula Ashcraft, Helen Wainwright, Anil Pooran, Teodoro Bottiglieri, and Prithvi Raj
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Adult ,Male ,0301 basic medicine ,Pulmonary and Respiratory Medicine ,Tuberculosis ,Adolescent ,Treatment adherence ,Biopsy ,030106 microbiology ,Antitubercular Agents ,Microbial Sensitivity Tests ,Drug resistance ,Critical Care and Intensive Care Medicine ,Drug penetration ,Young Adult ,03 medical and health sciences ,Acquired resistance ,Tuberculosis, Multidrug-Resistant ,medicine ,Humans ,In patient ,Prospective Studies ,Lung ,Original Research ,Dose-Response Relationship, Drug ,business.industry ,Middle Aged ,medicine.disease ,Immunology ,Drug Therapy, Combination ,Female ,Lung cavity ,business - Abstract
Rationale: Acquired resistance is an important driver of multidrug-resistant tuberculosis (TB), even with good treatment adherence. However, exactly what initiates the resistance and how it arises remain poorly understood. Objectives: To identify the relationship between drug concentrations and drug susceptibility readouts (minimum inhibitory concentrations [MICs]) in the TB cavity. Methods: We recruited patients with medically incurable TB who were undergoing therapeutic lung resection while on treatment with a cocktail of second-line anti-TB drugs. On the day of surgery, antibiotic concentrations were measured in the blood and at seven prespecified biopsy sites within each cavity. Mycobacterium tuberculosis was grown from each biopsy site, MICs of each drug identified, and whole-genome sequencing performed. Spearman correlation coefficients between drug concentration and MIC were calculated. Measurements and Main Results: Fourteen patients treated for a median of 13 months (range, 5–31 mo) were recruited. MICs and drug resistance–associated single-nucleotide variants differed between the different geospatial locations within each cavity, and with pretreatment and serial sputum isolates, consistent with ongoing acquisition of resistance. However, pretreatment sputum MIC had an accuracy of only 49.48% in predicting cavitary MICs. There were large concentration–distance gradients for each antibiotic. The location-specific concentrations inversely correlated with MICs (P
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- 2018
9. Antitubercular 2-Pyrazolylpyrimidinones: Structure-Activity Relationship and Mode-of-Action Studies
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Kirsteen I. Buchanan, Clifton E. Barry, Simon Green, Gregory S. Basarab, Qin Su, Charles J. Eyermann, Curtis A. Engelhart, Anuradha Kumar, Paul D. van Helden, Frederick A. Sirgel, Paul G. Wyatt, Nina Lawrence, Sandeep R. Ghorpade, Dirk Schnappinger, Dale Taylor, Sandile B. Simelane, Helena I. Boshoff, Christel Brunschwig, Vinayak Singh, Kelly Chibale, Peter C. Ray, Tracy Bayliss, Candice Soares de Melo, Alissa Myrick, Tanya Parish, and Timothy G. Myers
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Male ,Phenotypic screening ,Iron ,Mutant ,Antitubercular Agents ,Microbial Sensitivity Tests ,Pyrimidinones ,01 natural sciences ,Article ,Mycobacterium tuberculosis ,03 medical and health sciences ,Minimum inhibitory concentration ,Mice ,Structure-Activity Relationship ,Bacterial Proteins ,Microsomes ,Drug Discovery ,medicine ,Structure–activity relationship ,Animals ,Humans ,Mode of action ,030304 developmental biology ,0303 health sciences ,biology ,Chemistry ,Membrane Transport Proteins ,biology.organism_classification ,In vitro ,0104 chemical sciences ,Rats ,Mice, Inbred C57BL ,010404 medicinal & biomolecular chemistry ,Biochemistry ,Mechanism of action ,Mutation ,Molecular Medicine ,Pyrazoles ,medicine.symptom ,Half-Life - Abstract
Phenotypic screening of a Medicines for Malaria Venture compound library against Mycobacterium tuberculosis (Mtb) identified a cluster of pan-active 2-pyrazolylpyrimidinones. The biology triage of these actives using various tool strains of Mtb suggested a novel mechanism of action. The compounds were bactericidal against replicating Mtb and retained potency against clinical isolates of Mtb. Although selected MmpL3 mutant strains of Mtb showed resistance to these compounds, there was no shift in the minimum inhibitory concentration (MIC) against a mmpL3 hypomorph, suggesting mutations in MmpL3 as a possible resistance mechanism for the compounds but not necessarily as the target. RNA transcriptional profiling and the checkerboard board 2D-MIC assay in the presence of varying concentrations of ferrous salt indicated perturbation of the Fe-homeostasis by the compounds. Structure-activity relationship studies identified potent compounds with good physicochemical properties and in vitro microsomal metabolic stability with moderate selectivity over cytotoxicity against mammalian cell lines.
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- 2021
10. Rifampicin-monoresistant tuberculosis is not the same as multidrug-resistant tuberculosis : a descriptive study from Khayelitsha, South Africa
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Sebastien Gagneux, Helen Cox, Anzaan Dippenaar, Sonia Borrell, Frederick A. Sirgel, Zubeida Salaam-Dreyer, Mark P. Nicol, Erika Mohr-Holland, Elizabeth M. Streicher, Robin M. Warren, Anna Doetsch, Patrick G T Cudahy, Miriam Reinhard, Fabrizio Menardo, and Johnny Daniels
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medicine.medical_specialty ,Tuberculosis ,Antitubercular Agents ,HIV Infections ,MDR-TB ,Microbial Sensitivity Tests ,Drug resistance ,Epidemiology and Surveillance ,Mycobacterium tuberculosis ,South Africa ,Internal medicine ,Tuberculosis, Multidrug-Resistant ,Isoniazid ,medicine ,Humans ,Pharmacology (medical) ,Biology ,Pharmacology ,drug resistance ,human immunodeficiency virus ,biology ,business.industry ,Pharmacology. Therapy ,rifampin-monoresistant TB ,Odds ratio ,Editor's Pick ,biology.organism_classification ,rpoB ,medicine.disease ,multidrug-resistant TB ,Multiple drug resistance ,Infectious Diseases ,tuberculosis ,whole-genome sequencing ,Mutation ,drug resistance evolution ,Rifampin ,business ,Rifampicin ,medicine.drug - Abstract
Rifampin monoresistance (RMR; rifampin resistance and isoniazid susceptibility) accounts for 38% of all rifampin-resistant tuberculosis (RR-TB) in South Africa and is increasing. We aimed to compare RMR-TB with multidrug-resistant TB (MDR-TB) in a setting with high TB, RR-TB, and HIV burdens. Patient-level clinical data and stored RR Mycobacterium tuberculosis isolates from 2008 to 2017 with available whole-genome sequencing (WGS) data were used to describe risk factors associated with RMR-TB and to compare RR-conferring mutations between RMR-TB and MDR-TB. A subset of isolates with particular RR-conferring mutations were subjected to semiquantitative rifampin phenotypic drug susceptibility testing. Among 2,041 routinely diagnosed RR-TB patients, 463 (22.7%) had RMR-TB. HIV-positive individuals (adjusted odds ratio [aOR], 1.4; 95% confidence interval [CI], 1.1 to 1.9) and diagnosis between 2013 and 2017 versus between 2008 and 2012 (aOR, 1.3; 95% CI, 1.1 to 1.7) were associated with RMR-TB. Among 1,119 (54.8%) patients with available WGS data showing RR-TB, significant differences in the distribution of rpoB RR-conferring mutations between RMR and MDR isolates were observed. Mutations associated with high-level RR were more commonly found among MDR isolates (811/889 [90.2%] versus 162/230 [70.4%] among RMR isolates; P < 0.0001). In particular, the rpoB L430P mutation, conferring low-level RR, was identified in 32/230 (13.9%) RMR isolates versus 10/889 (1.1%) in MDR isolates (P < 0.0001). Among 10 isolates with an rpoB L430P mutation, 7 were phenotypically susceptible using the critical concentration of 0.5 mu g/ml (range, 0.125 to 1 mu g/ml). The majority (215/230 [93.5%]) of RMR isolates showed susceptibility to all other TB drugs, highlighting the potential benefits of WGS for simplified treatment. These data suggest that the evolution of RMR-TB differs from MDR-TB with a potential contribution from HIV infection.
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- 2021
11. The rationale for using rifabutin in the treatment of MDR and XDR tuberculosis outbreaks.
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Frederick A Sirgel, Robin M Warren, Erik C Böttger, Marisa Klopper, Thomas C Victor, and Paul D van Helden
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Medicine ,Science - Abstract
Genetically related Mycobacterium tuberculosis strains with alterations at codon 516 in the rpoB gene were observed amongst a substantial number of patients with drug resistant tuberculosis in the Eastern Cape Province (ECP) of South Africa. Mutations at codon 516 are usually associated with lower level rifampicin (RIF) resistance, while susceptibility to rifabutin (RFB) remains intact. This study was conducted to assess the rationale for using RFB as a substitution for RIF in the treatment of MDR and XDR tuberculosis outbreaks. Minimum inhibitory concentrations (MICs) of 34 drug resistant clinical isolates of M tuberculosis were determined by MGIT 960 and correlated with rpoB mutations. RFB MICs ranged from 0.125 to 0.25 µg/ml in the 34 test isolates thereby confirming phenotypic susceptibility as per critical concentration (CC) of 0.5 µg/ml. The corresponding RIF MICs ranged between 5 and 15 µg/ml, which is well above the CC of 1.0 µg/ml. Molecular-based drug susceptibility testing provides important pharmacogenetic insight by demonstrating a direct correlation between defined rpoB mutation and the level of RFB susceptibility. We suggest that isolates with marginally reduced susceptibility as compared to the epidemiological cut-off for wild-type strains (0.064 µg/ml), but lower than the current CC (≤0.5 µg/ml), are categorised as intermediate. Two breakpoints (0.064 µg/ml and 0.5 µg/ml) are recommended to distinguish between susceptible, intermediate and RFB resistant strains. This concept may assist clinicians and policy makers to make objective therapeutic decisions, especially in situations where therapeutic options are limited. The use of RFB in the ECP may improve therapeutic success and consequently minimise the risk of ongoing transmission of drug resistant M. tuberculosis strains.
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- 2013
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12. Discordances between molecular assays for rifampicin resistance in Mycobacterium tuberculosis: frequency, mechanisms and clinical impact
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Robin M. Warren, Elise De Vos, Frederick A. Sirgel, Lesley Scott, Wendy S. Stevens, Cindy Hayes, Annelies Van Rie, Pedro Da Silva, Tim H. Heupink, and Michael G. Whitfield
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0301 basic medicine ,Microbiology (medical) ,medicine.medical_specialty ,Tuberculosis ,030106 microbiology ,Rifampicin resistance ,Sensitivity and Specificity ,Mycobacterium tuberculosis ,03 medical and health sciences ,0302 clinical medicine ,Internal medicine ,Clinical information ,Drug Resistance, Bacterial ,Tuberculosis, Multidrug-Resistant ,medicine ,Humans ,Pharmacology (medical) ,030212 general & internal medicine ,Antibiotics, Antitubercular ,Biology ,Original Research ,Pharmacology ,High rate ,biology ,Treatment regimen ,business.industry ,Pharmacology. Therapy ,medicine.disease ,biology.organism_classification ,Infectious Diseases ,Cohort ,Human medicine ,Rifampin ,business ,Rifampicin ,medicine.drug - Abstract
Background Molecular assays are endorsed for detection and confirmation of rifampicin-resistant TB. The frequency, causal mechanisms and impact of discordant results between molecular tests are not well understood. Methods The prevalence of discordant results was determined by pairwise comparison of molecular test results in a cohort of 749 rifampicin-resistant TB patients in three South African provinces. Culture isolates were sent to a research laboratory for WGS and rifampicin MIC determination. Clinical information was collected through medical file review. Results The prevalence of discordances between Xpert MTB/RIF and MTBDRplus was 14.5% (95% CI 10.9%–18.9%), 5.6% (95% CI 2.2%–13.4%) between two consecutive Xpert assays and 4.2% (95% CI 2.2%–7.8%) between two consecutive MTBDRplus assays. Likely mechanisms of discordances were false rifampicin susceptibility on MTBDRplus (due to variants not included in mutant probes or heteroresistance with loss of minor variants in culture), false resistance on molecular assay in rifampicin-susceptible isolates, and human error. The healthcare worker changed the treatment regimen in 33% of patients with discordant results and requested 232 additional molecular tests after a first confirmatory test was performed in 460 patients. A follow-up Xpert assay would give the healthcare worker the ‘true’ rifampicin-resistant TB diagnosis in at least 73% of discordant cases. Conclusions The high rate of discordant results between Xpert and MTBDRplus has important implications for the laboratory, clinician and patient. While root causes for discordant result are multiple, a follow-up Xpert assay could guide healthcare workers to the correct treatment in most patients.
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- 2020
13. Minority
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David M, Engelthaler, Elizabeth M, Streicher, Erin J, Kelley, Christopher J, Allender, Kristin, Wiggins, Dulce, Jimenez, Darrin, Lemmer, Eric, Vittinghoff, Grant, Theron, Frederick A, Sirgel, Robin M, Warren, and John Z, Metcalfe
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DNA, Bacterial ,Genotype ,Antitubercular Agents ,High-Throughput Nucleotide Sequencing ,Mycobacterium tuberculosis ,Proof of Concept Study ,Bacterial Proteins ,DNA Gyrase ,Drug Resistance, Multiple, Bacterial ,Tuberculosis, Multidrug-Resistant ,Correspondence ,Humans ,Selection, Genetic ,Genetic Association Studies ,Retrospective Studies - Published
- 2019
14. The potential use of rifabutin for treatment of patients diagnosed with rifampicin-resistant tuberculosis
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Wendy Stevens, Lesley Scott, Guido Groenen, Elizabeth M. Streicher, Elise De Vos, Robin M. Warren, Michael G. Whitfield, Vanessa Mathys, Frederick A. Sirgel, and Annelies Van Rie
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0301 basic medicine ,Microbiology (medical) ,medicine.medical_specialty ,Rifabutin ,Tuberculosis ,medicine.drug_class ,030106 microbiology ,Antibiotics ,Microbial Sensitivity Tests ,law.invention ,South Africa ,03 medical and health sciences ,Bacterial Proteins ,Belgium ,Randomized controlled trial ,law ,Polymorphism (computer science) ,Internal medicine ,Tuberculosis, Multidrug-Resistant ,parasitic diseases ,polycyclic compounds ,medicine ,Humans ,Pharmacology (medical) ,Biology ,Antibiotics, Antitubercular ,Original Research ,Pharmacology ,Polymorphism, Genetic ,business.industry ,Pharmacology. Therapy ,DNA-Directed RNA Polymerases ,Mycobacterium tuberculosis ,bacterial infections and mycoses ,rpoB ,medicine.disease ,Regimen ,Infectious Diseases ,Mutation ,Human medicine ,Rifampin ,business ,Rifampicin ,medicine.drug - Abstract
Background: Use of the Xpert MTB/RIF assay has increased the number of people diagnosed with rifampicin-resistant tuberculosis (RR-TB), especially in South Africa where Xpert is now the initial diagnostic for individuals with TB symptoms. We hypothesized that a proportion of RR-TB patients determined by Xpert can be treated with a rifabutin-containing regimen. Methods: Rifabutin susceptibility by rpoB mutation was assessed in 349 individuals from South Africa and 172 from Belgium. rpoB polymorphisms were identified by Sanger sequencing. Rifampicin and rifabutin susceptibility was assessed phenotypically. A systematic review was performed to comprehensively collate information on rifabutin susceptibility by rpoB polymorphism. Rifabutin susceptibility was assigned to rpoB polymorphisms based on their positive likelihood ratios and ORs. Results: One hundred and twelve rpoB polymorphisms (67.9% from literature) were identified from all 2045 RR-TB patients, of which 17 polymorphisms could be classified as susceptible/resistant to rifabutin. Eleven polymorphisms were associated with rifabutin susceptibility. The 516GTC mutation was the most common, representing 70% (South Africa) and 76% (Be(gium) of all rifabutin-susceptible isolates. At a population level, the 11 polymorphisms associated with rifabutin susceptibility occurred in 33.2% and 16.6% of all South African and Belgian patients diagnosed with RR-TB, respectively. Conclusions: Identification of the exact rpoB polymorphism leading to the diagnosis of RR-TB has the potential to allow inclusion of rifabutin in the treatment regimen of a substantial proportion of RR-TB patients. A randomized controlled trial evaluating the efficacy of a rifabutin-containing TB treatment regimen in these selected patients is needed to provide the evidence required for a change in policy.
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- 2018
15. Outcomes, infectiousness, and transmission dynamics of patients with extensively drug-resistant tuberculosis and home-discharged patients with programmatically incurable tuberculosis: a prospective cohort study
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Aliasgar Esmail, Robin M. Warren, Maia Lesosky, Ruth McNerney, Tawanda Gumbo, Julian te Riele, Taane G. Clark, Fathia Ben-Rached, Jason Limberis, Liezel Smith, Jody Phelan, Barbara Lazaro Mastrapa, Frederick A. Sirgel, Tania Dolby, John M. Simpson, Paul D. van Helden, Kevin P. Fennelly, Arnab Pain, Elize Pietersen, Elizabeth M. Streicher, Keertan Dheda, Abdallah M. Abdallah, and Grant Theron
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Adult ,Male ,Pulmonary and Respiratory Medicine ,medicine.medical_specialty ,Rifabutin ,Tuberculosis ,Extensively Drug-Resistant Tuberculosis ,Antitubercular Agents ,South Africa ,03 medical and health sciences ,chemistry.chemical_compound ,0302 clinical medicine ,medicine ,Humans ,Prospective Studies ,Treatment Failure ,030212 general & internal medicine ,Intensive care medicine ,Prospective cohort study ,business.industry ,Sputum ,Extensively drug-resistant tuberculosis ,Mycobacterium tuberculosis ,medicine.disease ,Patient Discharge ,Clinical trial ,Regimen ,Phenotype ,030228 respiratory system ,chemistry ,Emergency medicine ,Female ,Delamanid ,Bedaquiline ,business ,Follow-Up Studies ,medicine.drug - Abstract
The emergence of programmatically incurable tuberculosis threatens to destabilise control efforts. The aim of this study was to collect prospective patient-level data to inform treatment and containment strategies.In a prospective cohort study, 273 South African patients with extensively drug-resistant tuberculosis, or resistance beyond extensively drug-resistant tuberculosis, were followed up over a period of 6 years. Transmission dynamics, infectiousness, and drug susceptibility were analysed in a subset of patients from the Western Cape using whole-genome sequencing (WGS; n=149), a cough aerosol sampling system (CASS; n=26), and phenotypic testing for 18 drugs (n=179).Between Oct 1, 2008, and Oct 31, 2012, we enrolled and followed up 273 patients for a median of 20·3 months (IQR 9·6-27·8). 203 (74%) had programmatically incurable tuberculosis and unfavourable outcomes (treatment failure, relapse, default, or death despite treatment with a regimen based on capreomycin, aminosalicylic acid, or both). 172 (63%) patients were discharged home, of whom 104 (60%) had an unfavourable outcome. 54 (31%) home-discharged patients had failed treatment, with a median time to death after discharge of 9·9 months (IQR 4·2-17·4). 35 (20%) home-discharged cases were smear-positive at discharge. Using CASS, six (23%) of 26 home-discharged cases with data available expectorated infectious culture-positive cough aerosols in the respirable range (5 μm), and most reported inter-person contact with suboptimal protective mask usage. WGS identified 17 (19%) of the 90 patients (with available sequence data) that were discharged home before the diagnosis of 20 downstream cases of extensively drug-resistant tuberculosis with almost identical sequencing profiles suggestive of community-based transmission (five or fewer single nucleotide polymorphisms different and with identical resistance-encoding mutations for 14 drugs). 11 (55%) of these downstream cases had HIV co-infection and ten (50%) had died by the end of the study. 22 (56%) of 39 isolates in patients discharged home after treatment failure were resistant to eight or more drugs. However, five (16%) of 31 isolates were susceptible to rifabutin and more than 90% were likely to be sensitive to linezolid, bedaquiline, and delamanid.More than half of the patients with programmatically incurable tuberculosis were discharged into the community where they remained for an average of 16 months, were at risk of expectorating infectious cough aerosols, and posed a threat of transmission of extensively drug-resistant tuberculosis. Urgent action, including appropriate containment strategies, is needed to address this situation. Access to delamanid, bedaquiline, linezolid, and rifabutin, when appropriate, must be accelerated along with comprehensive drug susceptibility testing.UK Medical Research Council, South African Medical Research Council, South African National Research Foundation, EuropeanDeveloping Countries Clinical Trials Partnership, Oppenheimer Foundation, Newton Fund, Biotechnology and Biological Sciences Research Council, King Abdullah University of ScienceTechnology.
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- 2017
16. Linezolid Pharmacokinetics in South African Patients with Drug-Resistant Tuberculosis and a High Prevalence of HIV Coinfection
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Keertan Dheda, James C.M. Brust, Aliasgar Esmail, Sean Wasserman, Graeme Meintjes, Siphokazi Hlungulu, Neel R. Gandhi, Frederick A. Sirgel, Robin M. Warren, Lubbe Wiesner, Paolo Denti, Jennifer Norman, Gary Maartens, and Mahmoud Tareq Abdelwahab
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Adult ,Male ,medicine.medical_specialty ,Tuberculosis ,Antitubercular Agents ,Microbial Sensitivity Tests ,Clinical Therapeutics ,03 medical and health sciences ,chemistry.chemical_compound ,South Africa ,0302 clinical medicine ,Pharmacokinetics ,Internal medicine ,Tuberculosis, Multidrug-Resistant ,medicine ,Humans ,Pharmacology (medical) ,Trough Concentration ,030212 general & internal medicine ,Dosing ,Prospective Studies ,Tuberculosis, Pulmonary ,Pharmacology ,0303 health sciences ,030306 microbiology ,business.industry ,Linezolid ,Liter ,Mycobacterium tuberculosis ,medicine.disease ,Confidence interval ,3. Good health ,Infectious Diseases ,chemistry ,Pharmacodynamics ,Female ,business - Abstract
The World Health Organization (WHO) recently recommended that linezolid be prioritized in treatment regimens for drug-resistant tuberculosis (TB), but there are limited data on its pharmacokinetics (PK) in patients with this disease. We conducted an observational study to explore covariate effects on linezolid PK and to estimate the probability of PK/pharmacodynamic target attainment in South African patients with drug-resistant TB. Consecutive adults on linezolid-based regimens were recruited in Cape Town and underwent intensive PK sampling at steady state. Noncompartmental analysis was performed. Thirty participants were included: 15 HIV positive, 26 on the initial dose of 600 mg daily, and 4 participants on 300 mg daily after dose reduction for linezolid-related toxicity. There was a negative correlation between body weight and exposure, with 17.4% (95% confidence interval [CI], 0.1 to 31.7) decrease in area under the concentration-time curve from 0 to 24 h (AUC0–24) per 10-kg weight increment after adjustment for other covariates. Age was an independent predictor of trough concentration, with an estimated 43.4% (95% CI, 5.9 to 94.2) increase per 10-year increment in age. The standard 600-mg dose achieved the efficacy target of free AUC/MIC of >119 at wild-type MIC values (≤0.5 mg/liter), but the probability of target attainment dropped to 61.5% (95% CI, 40.6 to 79.8) at the critical concentration of 1 mg/liter. When dosed at 600 mg daily, trough concentrations were above the toxicity threshold of 2 mg/liter in 57.7% (95% CI, 36.9 to 76.6). This confirms the narrow therapeutic index of linezolid, and alternative dosing strategies should be explored.
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- 2019
17. High frequency of bedaquiline resistance in programmatically treated drug-resistant TB patients with sustained culture-positivity in Cape Town, South Africa
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Grant Theron, Rob Warren, Rudi Alberts, Frederick A. Sirgel, Brigitta Derendinger, Helen Cox, Anzaan Dippenaar, Claudia Spies, David Engelthaler, Margaretha de Vos, Tania Dolby, Leen Rigouts, and John Metcalfe
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Microbiology (medical) ,Drug ,medicine.medical_specialty ,education.field_of_study ,Tuberculosis ,biology ,business.industry ,media_common.quotation_subject ,Population ,Drug resistance ,biology.organism_classification ,medicine.disease ,Mycobacterium tuberculosis ,Clofazimine ,chemistry.chemical_compound ,Regimen ,Infectious Diseases ,chemistry ,Internal medicine ,Medicine ,Bedaquiline ,business ,education ,media_common ,medicine.drug - Abstract
Aims & objectives: Potentially transformative new tuberculosis (TB) drugs like bedaquiline are undergoing roll-out, however, this is largely in the absence of programmatic drug susceptibility testing (DST). We lack information on how susceptibility changes during treatment in patients on bedaquiline-containing regimens, especially in at risk patients who have complex treatment histories, are in programmatic rather than trial environments, and have a delayed treatment response (defined here as sustained culture-positivity). Methods: Serial isolates from 51 patients with drug resistant (DR-)TB who were culture-positive after ≥4 months of a programmatically administered bedaquiline-containing regimen, were collected. Bedaquiline phenotypic DST in MGIT 960 (1μg/ml), targeted deep sequencing (Rv0678, atpE, pepQ) and whole genome sequencing was done on paired isolates (pre-bedaquiline initiation, post-four-month). Results: 24/51 (47%) patients were phenotypically and genotypically resistant (39% acquired resistance). Excluding one patient with an unknown history, prior clofazimine exposure was associated with bedaquiline-resistance [21/24 (88%) bedaquiline resistant cases had prior clofazimine vs. 12/26 (46%) susceptibles; p=0.002]. Diverse combinations of single nucleotide polymorphisms (SNPs) and indels were in the Rv0678 promoter region and the Rv0678 and atpE genes. Examples of newly described resistance associated variants (RAVs) include Rv0678 -8 T/G and atpE 223 C/T. RAVs were not in defined hotspots and sometimes occurred concurrently with atpE RAVs. Discussion: The rate of bedaquiline resistance acquisition in this population is alarmingly high and associated with prior clofazimine exposure. The diverse RAVs pose challenges to molecular test development. This study highlights the existence of a potentially infectious pool of bedaquiline-resistant patients present under programmatic conditions in a resource-constrained setting and illustrates the danger of starting patients with complex histories on a novel drug without routinely available DST.
- Published
- 2021
18. Impact of Nonlinear Interactions of Pharmacokinetics and MICs on Sputum Bacillary Kill Rates as a Marker of Sterilizing Effect in Tuberculosis
- Author
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Paul D. van Helden, Frederick A. Sirgel, Emmanuel Chigutsa, Pete Smith, Tawanda Gumbo, Helen McIlleron, Marianne E Visser, and Jotam G. Pasipanodya
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Adult ,Male ,Tuberculosis ,Adolescent ,medicine.drug_class ,Antibiotics ,Antitubercular Agents ,Cmax ,HIV Infections ,Microbial Sensitivity Tests ,Clinical Therapeutics ,Pharmacology ,Young Adult ,Pharmacokinetics ,Isoniazid ,medicine ,Humans ,Pharmacology (medical) ,Ethambutol ,business.industry ,Sputum ,Sterilization ,Drug Synergism ,Mycobacterium tuberculosis ,Middle Aged ,Pyrazinamide ,medicine.disease ,Disinfection ,Treatment Outcome ,Infectious Diseases ,Area Under Curve ,Drug Therapy, Combination ,Female ,Rifampin ,medicine.symptom ,business ,Drug Antagonism ,medicine.drug - Abstract
The relationships between antituberculosis drug exposure and treatment effects on humans receiving multidrug therapy are complex and nonlinear. In patients on treatment, an analysis of the rate of decline in the sputum bacillary burden reveals two slopes. The first is the α-slope, which is thought to reflect bactericidal effect, followed by a β-slope, which is thought to reflect sterilizing activity. We sought to characterize the effects of standard first-line treatment on sterilizing activity. Fifty-four patients receiving combination therapy for pulmonary tuberculosis in a clinical trial had drug concentrations measured and Mycobacterium tuberculosis isolates available for MIC identification. Sputum sample cultures were performed at baseline and weekly for 8 weeks. A time-to-event model based on the days to positivity in the liquid cultures was used to estimate the β-slope. The pharmacokinetic parameters of rifampin, isoniazid, ethambutol, and pyrazinamide were determined for each patient. Multivariate adaptive regression splines analyses, which simultaneously perform linear and nonlinear analyses, were used to identify the relationships between the predictors and the β-slope. The potential predictors examined included HIV status, lung cavitation, 24-h area under the concentration-time curve (AUC), peak drug concentration ( C max ), AUC/MIC ratio, C max /MIC ratio, and the time that that concentration persisted above MIC. A rifampin C max of >8.2 mg/liter and a pyrazinamide AUC/MIC of >11.3 were key predictors of the β-slope and interacted positively to increase the β-slope. In patients with a rifampin AUC of C max /MIC increased the β-slope, while increasing isoniazid C max decreased it, suggesting isoniazid antagonism. Antibiotic concentrations and MICs interact in a nonlinear fashion as the main drivers of a sterilizing effect. The results suggest that faster speeds of sterilizing effect might be achieved by omitting isoniazid and by increasing rifampin, pyrazinamide, and ethambutol exposures. However, isoniazid and ethambutol exposures may only be of importance when rifampin exposure is low. These findings need confirmation in larger studies. (This study has been registered at controlled-trials.com under registration no. ISRCTN80852505.)
- Published
- 2015
19. The pyrazinamide susceptibility breakpoint above which combination therapy fails
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Jotam G. Pasipanodya, Tawanda Gumbo, Helen McIlleron, Paul D. van Helden, Frederick A. Sirgel, Marianne E Visser, and Emmanuel Chigutsa
- Subjects
Adult ,Male ,Microbiology (medical) ,Oncology ,medicine.medical_specialty ,MICs ,Adolescent ,genetic structures ,Combination therapy ,Antitubercular Agents ,Microbial Sensitivity Tests ,Pharmacology ,drug susceptibility ,South Africa ,Young Adult ,03 medical and health sciences ,0302 clinical medicine ,Internal medicine ,anti-tuberculosis drugs ,Drug Resistance, Bacterial ,medicine ,Humans ,Combined Modality Therapy ,Pharmacology (medical) ,030212 general & internal medicine ,Tuberculosis, Pulmonary ,Ethambutol ,Original Research ,0303 health sciences ,sputum culture ,030306 microbiology ,business.industry ,Breakpoint ,Sputum ,Mycobacterium tuberculosis ,Drug susceptibility ,Middle Aged ,Pyrazinamide ,3. Good health ,Treatment Outcome ,Infectious Diseases ,Drug Therapy, Combination ,Female ,Sputum Cytology Screening ,business ,pharmacokinetics ,medicine.drug - Abstract
Objectives To identify the pyrazinamide MIC above which standard combination therapy fails. Methods MICs of pyrazinamide were determined for Mycobacterium tuberculosis isolates, cultured from 58 patients in a previous randomized clinical trial in Cape Town, South Africa. The MICs were determined using BACTEC MGIT 960 for isolates that were collected before standard treatment with isoniazid, rifampicin, pyrazinamide and ethambutol commenced. Weekly sputum collections were subsequently made for 8 weeks in order to culture M. tuberculosis in Middlebrook broth medium. Classification and regression tree (CART) analysis was utilized to identify the pyrazinamide MIC predictive of sputum culture results at the end of pyrazinamide therapy. The machine learning-derived susceptibility breakpoints were then confirmed using standard association statistics that took into account confounders of 2 month sputum conversion. Results The pyrazinamide MIC range was 12.5 to >100 mg/L for the isolates prior to therapy. The epidemiological 95% cut-off value was >100 mg/L. The 2 month sputum conversion rate in liquid cultures was 26% by stringent criteria and 48% by less stringent criteria. CART analysis identified an MIC breakpoint of 50 mg/L, above which patients had poor sputum conversion rates. The relative risk of poor sputum conversion was 1.5 (95% CI: 1.2–1.8) for an MIC >50 mg/L compared with an MIC ≤50 mg/L. Conclusions We propose a pyrazinamide susceptibility breakpoint of 50 mg/L for clinical decision making and for development of rapid susceptibility assays. This breakpoint is identical to that identified using computer-aided simulations of hollow fibre system output.
- Published
- 2014
20. Moxifloxacin Retains Antimycobacterial Activity in the Presence of gyrA Mutations
- Author
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Robin M. Warren, Paul D. van Helden, Frederick A. Sirgel, Nico C. Gey van Pittius, and Marieta McGrath
- Subjects
Tuberculosis ,medicine.drug_class ,Moxifloxacin ,Mutant ,Antitubercular Agents ,Microbial Sensitivity Tests ,medicine.disease_cause ,Antimycobacterial ,DNA gyrase ,Microbiology ,Mycobacterium tuberculosis ,Bacterial Proteins ,Mechanisms of Resistance ,Drug Resistance, Bacterial ,medicine ,heterocyclic compounds ,Pharmacology (medical) ,Pharmacology ,Mutation ,biology ,Chemistry ,biochemical phenomena, metabolism, and nutrition ,bacterial infections and mycoses ,medicine.disease ,biology.organism_classification ,In vitro ,Infectious Diseases ,DNA Gyrase ,Fluoroquinolones ,medicine.drug - Abstract
Moxifloxacin-resistant Mycobacterium tuberculosis mutants were selected in vitro using different concentrations of moxifloxacin. gyrA mutations at codons 88 and 94 were associated with resistance (defined as an MIC of ≥2 μg/ml) ( P < 0.0001 and P = 0.0053, respectively). Despite the presence of gyrA mutations, moxifloxacin significantly impedes bacterial growth, supporting its use for the treatment of ofloxacin-resistant M. tuberculosis .
- Published
- 2014
21. Long-term outcomes of patients with extensively drug-resistant tuberculosis in South Africa: a cohort study
- Author
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Maia Lesosky, Motasim Badri, Barbara Lazaro Mastrapa, Keertan Dheda, Robin M. Warren, Paul D. van Helden, Anil Pooran, Elisa Ignatius, Frederick A. Sirgel, Elizabeth M. Streicher, Elize Pietersen, and Xavier Padanilam
- Subjects
Pediatrics ,medicine.medical_specialty ,Tuberculosis ,Palliative care ,medicine.diagnostic_test ,business.industry ,Extensively drug-resistant tuberculosis ,General Medicine ,medicine.disease ,Sputum culture ,medicine ,Culture conversion ,Sputum ,medicine.symptom ,Prospective cohort study ,business ,Cohort study - Abstract
Summary Background Long-term treatment-related outcomes in patients with extensively drug-resistant (XDR) tuberculosis are unknown. We followed up a cohort of patients to address knowledge gaps. (41%) had HIV. 36 (64%) of 56 isolates were resistant to at least eight drugs, and resistance to an increasing number of drugs was associated with the Beijing genotype (p=0·01). After 24 months of follow-up, 17 patients (16%) had a favourable outcome (ie, treatment cure or completion), 49 (46%) had died, seven (7%) had defaulted (interruption of treatment for at least 2 consecutive months), and 25 (23%) had failed treatment. At 60 months, 12 patients (11%) had a favourable outcome, 78 (73%) had died, four (4%) had defaulted, and 11 (10%) had failed treatment. 45 patients were discharged from hospital, of whom 26 (58%) had achieved sputum culture conversion and 19 (42%) had failed treatment. M edian survival of patients who had failed treatment from time of discharge was 19·84 months (IQR 4·16-26·04). Clustering of cases and transmission within families containing a patient who had failed treatment and been discharged were shown with genotypic methods. Net sputum culture conversion occurred in 22 patients (21%) and median time to net culture conversion was 8·7 months (IQR 5·6-26·4). Independent predictors of probability of net culture conversion were no history of multidrug-resistant tuberculosis (p=0·0007) and use of clofazamine (p=0·0069). Independent overall predictors of survival were net culture conversion (p
- Published
- 2014
22. Evaluation of the AID TB Resistance Line Probe Assay for Rapid Detection of Genetic Alterations Associated with Drug Resistance in Mycobacterium tuberculosis Strains
- Author
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Frederick A. Sirgel, R. W. Warren, Erik C. Böttger, P. D. van Helden, Katja Lucke, Claudia Ritter, and Guido V. Bloemberg
- Subjects
Microbiology (medical) ,Tuberculosis ,Capreomycin ,Antitubercular Agents ,Microbial Sensitivity Tests ,Drug resistance ,Sensitivity and Specificity ,Microbiology ,Mycobacterium tuberculosis ,South Africa ,Antibiotic resistance ,Drug Resistance, Bacterial ,medicine ,Humans ,Line Probe Assay ,Ethambutol ,Mycobacterium bovis ,biology ,Mycobacteriology and Aerobic Actinomycetes ,biology.organism_classification ,medicine.disease ,Virology ,Molecular Diagnostic Techniques ,Mutation ,Switzerland ,medicine.drug - Abstract
The rapid accurate detection of drug resistance mutations in Mycobacterium tuberculosis is essential for optimizing the treatment of tuberculosis and limiting the emergence and spread of drug-resistant strains. The TB Resistance line probe assay from Autoimmun Diagnostika GmbH (AID) (Strassburg, Germany) was designed to detect the most prevalent mutations that confer resistance to isoniazid, rifampin, streptomycin, amikacin, capreomycin, fluoroquinolones, and ethambutol. This assay detected resistance mutations in clinical M. tuberculosis isolates from areas with low and high levels of endemicity (Switzerland, n = 104; South Africa, n = 52) and in selected Mycobacterium bovis BCG 1721 mutant strains ( n = 5) with 100% accuracy. Subsequently, the line probe assay was shown to be capable of rapid genetic assessment of drug resistance in MGIT broth cultures, the results of which were in 100% agreement with those of DNA sequencing and phenotypic drug susceptibility testing. Finally, the line probe assay was assessed for direct screening of smear-positive clinical specimens. Screening of 98 clinical specimens demonstrated that the test gave interpretable results for >95% of them. Antibiotic resistance mutations detected in the clinical samples were confirmed by DNA sequencing. We conclude that the AID TB Resistance line probe assay is an accurate tool for the rapid detection of resistance mutations in cultured isolates and in smear-positive clinical specimens.
- Published
- 2014
23. Moxifloxacin Population Pharmacokinetics and Model-Based Comparison of Efficacy between Moxifloxacin and Ofloxacin in African Patients
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Salome Charalambous, Paolo Denti, Emmanuel Chigutsa, Stanley Mungofa, Amina Jindani, Lubbe Wiesner, Thomas S. Harrison, Mark Hatherill, Ulrika S. H. Simonsson, Simbarashe P. Zvada, Helen McIlleron, and Frederick A. Sirgel
- Subjects
Adult ,Male ,Ofloxacin ,Tuberculosis ,Moxifloxacin ,Population ,Antitubercular Agents ,Microbial Sensitivity Tests ,Population pharmacokinetics ,Pharmacology ,Mycobacterium tuberculosis ,Young Adult ,Pharmacokinetics ,Tuberculosis, Multidrug-Resistant ,medicine ,Humans ,heterocyclic compounds ,Pharmacology (medical) ,Pharmaceutical sciences ,education ,education.field_of_study ,biology ,business.industry ,biochemical phenomena, metabolism, and nutrition ,Middle Aged ,bacterial infections and mycoses ,biology.organism_classification ,medicine.disease ,Infectious Diseases ,Female ,business ,Monte Carlo Method ,Fluoroquinolones ,medicine.drug - Abstract
Pharmacokinetic exposure and the MIC of fluoroquinolones are important determinants of their efficacy against Mycobacterium tuberculosis . Population modeling was used to describe the steady-state plasma pharmacokinetics of moxifloxacin in 241 tuberculosis (TB) patients in southern Africa. Monte Carlo simulations were applied to obtain the area under the unbound concentration-time curve from 0 to 24 h ( f AUC 0–24 ) after daily doses of 400 mg or 800 mg moxifloxacin and 800 mg ofloxacin. The MIC distributions of ofloxacin and moxifloxacin were determined for 197 drug-resistant clinical isolates of Mycobacterium tuberculosis . For a specific MIC, the probability of target attainment (PTA) was determined for target f AUC 0–24 /MIC ratios of ≥53 and ≥100. The PTAs were combined with the MIC distributions to calculate the cumulative fraction of response (CFR) for multidrug-resistant (MDR) Mycobacterium tuberculosis strains. Even with the less stringent target ratio of ≥53, moxifloxacin at 400 mg and ofloxacin at 800 mg achieved CFRs of only 84% and 58% for multidrug-resistant isolates with resistance to an injectable drug, while the 800-mg moxifloxacin dose achieved a CFR of 98%. Using a target ratio of ≥100 for multidrug-resistant strains (without resistance to injectable agents or fluoroquinolones), the CFR was 88% for moxifloxacin and only 43% for ofloxacin, and the higher dose of 800 mg moxifloxacin was needed to achieve a CFR target of >90%. Our results indicate that moxifloxacin is more efficacious than ofloxacin in the treatment of MDR-TB. Further studies should determine the optimal pharmacodynamic target for moxifloxacin in a multidrug regimen and clarify safety issues when it is administered at higher doses.
- Published
- 2014
24. Emergence and treatment of multidrug resistant (MDR) and extensively drug-resistant (XDR) tuberculosis in South Africa
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Kim G. P. Hoek, Paul D. van Helden, Frederick A. Sirgel, Thomas C. Victor, Manormoney Pillay, Andre Trollip, Marisa Tait, Elizabeth M. Streicher, Nicolaas C. Gey van Pittius, Robin M. Warren, Charmaine K. Mlambo, Borna Müller, and Violet N. Chihota
- Subjects
Microbiology (medical) ,Drug ,medicine.medical_specialty ,Delayed Diagnosis ,Tuberculosis ,Genotype ,Extensively Drug-Resistant Tuberculosis ,media_common.quotation_subject ,Antitubercular Agents ,Drug resistance ,Biology ,Microbiology ,South Africa ,Drug Resistance, Multiple, Bacterial ,Tuberculosis, Multidrug-Resistant ,Epidemiology ,Genetics ,medicine ,Culture conversion ,Humans ,Intensive care medicine ,Molecular Biology ,Ecology, Evolution, Behavior and Systematics ,media_common ,Molecular epidemiology ,business.industry ,Transmission (medicine) ,Mycobacterium tuberculosis ,medicine.disease ,Biotechnology ,Multiple drug resistance ,Phylogeography ,Infectious Diseases ,Practice Guidelines as Topic ,business - Abstract
Drug resistant tuberculosis (TB) has reached alarming proportions in South Africa, draining valuable resources that are needed to fight drug susceptible TB. It is currently estimated that 9.6% of all TB cases have multi-drug resistant (MDR)-TB, thereby ranking South Africa as one of the highest MDR-TB burden countries in the world. Molecular epidemiological studies have demonstrated the complexity of the epidemic and have clearly shown that the epidemic is driven by transmission as a consequence of low cases detection and diagnostic delay. The latter has in turn fueled the amplification of drug resistance, ultimately leading to the emergence of extensively drug resistant (XDR)-TB. Despite the introduction of new drugs to combat this scourge, culture conversion rates for XDR-TB remain below 20%. Failure to achieve cure may be explained from DNA sequencing results which have demonstrated mutations in 7 genes encoding resistance to at least 8 anti-TB drugs. This review shows how molecular epidemiology has provided novel insights into the MDR-TB epidemic in South Africa and thereby has highlighted the challenges that need to be addressed regarding the diagnosis and treatment of MDR-TB. An important step towards for curbing this epidemic will be collaboration between clinicians, laboratories and researchers to establish scientific knowledge and medical expertise to more efficiently guide public health policy.
- Published
- 2012
25. embB306 Mutations as Molecular Indicators to Predict Ethambutol Susceptibility in Mycobacterium tuberculosis
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Thomas C. Victor, Frederick A. Sirgel, Elizabeth M. Streicher, Robin M. Warren, Erik C. Böttger, and Paul D. van Helden
- Subjects
Pharmacology ,Susceptibility testing ,biology ,business.industry ,General Medicine ,Drug resistance ,bacterial infections and mycoses ,biology.organism_classification ,Mycobacterium tuberculosis ,Infectious Diseases ,Oncology ,Drug Discovery ,Immunology ,Mutation (genetic algorithm) ,Genotype ,medicine ,Pharmacology (medical) ,business ,Ethambutol ,medicine.drug - Abstract
Background: Discordant results in conventional susceptibility testing of ethambutol against Mycobacterium tuberculosis may lead to underreporting of drug resistance. Methods: A 240-bp region of the embB gene in 111 clinical isolates of M. tuberculosis was sequenced and examined for mutations linked to ethambutol resistance. The phenotypic susceptibility levels of the isolates were quantified by the BACTEC™ MGIT 960™ TB System and correlated with the genotypic test results. These data were analyzed to find information that could be used to clarify discordant ethambutol susceptibility test results. Results: Mutations M306I (n = 56), M306V (n = 18) and M306L (n = 3) in M. tuberculosis showed decreased susceptibility to ethambutol. The minimum inhibitory concentrations (MICs) in 73% (56/77) of embB306 mutants were at or just above the critical concentration (MICs, 5.0 to ≤12.5 µg/ml) of ethambutol reflecting borderline (or intermediate) resistance. Eight ethambutol-resistant isolates lacked embB mutations, probably due to mutational alterations elsewhere in the genome. Conclusion: Our findings suggest that clinical isolates containing embB306 mutations with MICs overlapping the critical concentration are associated with discordant ethambutol susceptibility test results. The clinical significance of borderline resistance in combination treatment of tuberculosis remains to be determined before alternative ethambutol breakpoints are considered.
- Published
- 2012
26. Pyrrolo[3,4-c]pyridine-1,3(2H)-diones: A Novel Antimycobacterial Class Targeting Mycobacterial Respiration
- Author
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Candice Soares de Melo, Renier van der Westhuyzen, Ujjini H. Manjunatha, Luca Arista, Atica Moosa, Grant A. Boyle, Leslie J. Street, Nina Lawrence, Christel Brunschwig, Frederick A. Sirgel, Richard K. Gessner, Paul W. Smith, Colin R. Wilson, Paul D. van Helden, Mathew Njoroge, Dale Taylor, Ronnett Seldon, Kelly Chibale, Srinivasa P. S. Rao, Carmen de Kock, Digby F. Warner, and Susan Winks
- Subjects
Cytochrome ,medicine.drug_class ,Stereochemistry ,Pyridones ,Antitubercular Agents ,Oxadiazole ,Antimycobacterial ,chemistry.chemical_compound ,Electron Transport Complex III ,Mice ,Oxidoreductase ,Drug Discovery ,medicine ,Animals ,Humans ,Tuberculosis ,Pyrroles ,Molecular Targeted Therapy ,chemistry.chemical_classification ,Oxidase test ,biology ,Chemistry ,Cytochrome c ,Mycobacterium tuberculosis ,Rats ,Coenzyme Q – cytochrome c reductase ,biology.protein ,Microsomes, Liver ,Molecular Medicine ,Bioisostere - Abstract
High-throughput screening of a library of small polar molecules against Mycobacterium tuberculosis led to the identification of a phthalimide-containing ester hit compound (1), which was optimized for metabolic stability by replacing the ester moiety with a methyl oxadiazole bioisostere. A route utilizing polymer-supported reagents was designed and executed to explore structure-activity relationships with respect to the N-benzyl substituent, leading to compounds with nanomolar activity. The frontrunner compound (5h) from these studies was well tolerated in mice. A M. tuberculosis cytochrome bd oxidase deletion mutant (ΔcydKO) was hyper-susceptible to compounds from this series, and a strain carrying a single point mutation in qcrB, the gene encoding a subunit of the menaquinol cytochrome c oxidoreductase, was resistant to compounds in this series. In combination, these observations indicate that this novel class of antimycobacterial compounds inhibits the cytochrome bc1 complex, a validated drug target in M. tuberculosis.
- Published
- 2015
27. The early bactericidal activity of a low-clearance liposomal amikacin in pulmonary tuberculosis
- Author
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Amour Venter, Bernard W. Van de Wal, Frederick A. Sirgel, D P Parkin, Peter R. Donald, Elizabeth Smit, and Denis A. Mitchison
- Subjects
Adult ,Male ,Microbiology (medical) ,Tuberculosis ,medicine.drug_class ,Antibiotics ,Pharmacology ,Minimum inhibitory concentration ,Confidence Intervals ,Humans ,Medicine ,Serum Bactericidal Test ,Pharmacology (medical) ,Amikacin ,Tuberculosis, Pulmonary ,Antibacterial agent ,Analysis of Variance ,Lung ,business.industry ,Aminoglycoside ,medicine.disease ,Anti-Bacterial Agents ,Infectious Diseases ,medicine.anatomical_structure ,Liposomes ,Immunology ,Regression Analysis ,Sputum ,medicine.symptom ,business ,medicine.drug - Abstract
The early bactericidal activity (EBA) of a liposomal preparation of amikacin (MiKasome) with a long plasma half-life of 120-200 h was examined in seven patients with newly diagnosed, smear-positive pulmonary tuberculosis. Liposomal amikacin was given in slow iv infusions of 30 mg total amikacin/kg body weight on three successive days. Cfu counts were set up on 16 h sputum collections preceding the first dose and following each dose and were used for calculating the EBA. Despite the high concentrations of total amikacin, >1000 mg/L, obtainable in plasma, no evidence of EBA was obtained. In view of the considerable activity of liposomal amikacin in experimental murine tuberculosis, this finding indicates that liberation of amikacin from the long-life liposomes occurs only in macrophages that are not usually present in the vicinity of the large extracellular clumps of bacilli in the cavity caseum.
- Published
- 2001
28. Emergence and spread of extensively and totally drug-resistant tuberculosis, South Africa
- Author
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Robin M. Warren, Cindy Hayes, Elizabeth M. Streicher, Andre Trollip, Nicolaas C. Gey van Pittius, Borna Müller, Paul D. van Helden, Mamisa Chabula-Nxiweni, Gerrit Coetzee, Frederick A. Sirgel, Marisa Klopper, Thomas C. Victor, and E Hoosain
- Subjects
Epidemiology ,Extensively Drug-Resistant Tuberculosis ,Antitubercular Agents ,lcsh:Medicine ,Totally drug-resistant tuberculosis ,Drug resistance ,Communicable Diseases, Emerging ,South Africa ,Genotype ,Cluster Analysis ,bacteria ,0303 health sciences ,multidrug-resistant tuberculosis ,Catalase ,3. Good health ,Infectious Diseases ,TB ,DNA profiling ,Microbiology (medical) ,totally drug-resistant tuberculosis ,Tuberculosis ,mycobacteria ,Mutation, Missense ,MDR-TB ,Microbial Sensitivity Tests ,Biology ,DNA sequencing ,Microbiology ,lcsh:Infectious and parasitic diseases ,Mycobacterium tuberculosis ,03 medical and health sciences ,Bacterial Proteins ,medicine ,Humans ,lcsh:RC109-216 ,XDR-TB ,Tuberculosis, Pulmonary ,030304 developmental biology ,totally drug resistant TB ,030306 microbiology ,Research ,lcsh:R ,Extensively drug-resistant tuberculosis ,medicine.disease ,biology.organism_classification ,Virology ,MDR TB - Abstract
Factors driving the increase in drug-resistant tuberculosis (TB) in the Eastern Cape Province, South Africa, are not understood. A convenience sample of 309 drug-susceptible and 342 multidrug-resistant (MDR) TB isolates, collected July 2008-July 2009, were characterized by spoligotyping, DNA fingerprinting, insertion site mapping, and targeted DNA sequencing. Analysis of molecular-based data showed diverse genetic backgrounds among drug-sensitive and MDR TB sensu stricto isolates in contrast to restricted genetic backgrounds among pre-extensively drug-resistant (pre-XDR) TB and XDR TB isolates. Second-line drug resistance was significantly associated with the atypical Beijing genotype. DNA fingerprinting and sequencing demonstrated that the pre-XDR and XDR atypical Beijing isolates evolved from a common progenitor; 85% and 92%, respectively, were clustered, indicating transmission. Ninety-three percent of atypical XDR Beijing isolates had mutations that confer resistance to 10 anti-TB drugs, and some isolates also were resistant to para-aminosalicylic acid. These findings suggest the emergence of totally drug-resistant TB.
- Published
- 2013
29. The Rationale for Using Rifabutin in the Treatment of MDR and XDR Tuberculosis Outbreaks
- Author
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Thomas C. Victor, Frederick A. Sirgel, Erik C. Böttger, Marisa Klopper, Paul D. van Helden, Robin M. Warren, and University of Zurich
- Subjects
Bacterial Diseases ,Rifabutin ,lcsh:Medicine ,Drug resistance ,South Africa ,Nucleic Acids ,Tuberculosis, Multidrug-Resistant ,Molecular Cell Biology ,lcsh:Science ,Multidisciplinary ,biology ,10179 Institute of Medical Microbiology ,Drug Information ,Bacterial Pathogens ,Infectious Diseases ,Medical Microbiology ,Medicine ,Public Health ,Rifampin ,medicine.drug ,Research Article ,Drugs and Devices ,Tuberculosis ,Drug Research and Development ,Mutation, Missense ,610 Medicine & health ,1100 General Agricultural and Biological Sciences ,Microbial Sensitivity Tests ,Microbiology ,Mycobacterium tuberculosis ,Species Specificity ,1300 General Biochemistry, Genetics and Molecular Biology ,Microbial Control ,Drug Resistance, Bacterial ,medicine ,Humans ,Biology ,business.industry ,lcsh:R ,Extensively drug-resistant tuberculosis ,Correction ,Drug Policy ,rpoB ,medicine.disease ,biology.organism_classification ,Virology ,Pharmacodynamics ,Pharmacogenetics ,570 Life sciences ,bacteria ,lcsh:Q ,business ,Rifampicin - Abstract
Genetically related Mycobacterium tuberculosis strains with alterations at codon 516 in the rpoB gene were observed amongst a substantial number of patients with drug resistant tuberculosis in the Eastern Cape Province (ECP) of South Africa. Mutations at codon 516 are usually associated with lower level rifampicin (RIF) resistance, while susceptibility to rifabutin (RFB) remains intact. This study was conducted to assess the rationale for using RFB as a substitution for RIF in the treatment of MDR and XDR tuberculosis outbreaks. Minimum inhibitory concentrations (MICs) of 34 drug resistant clinical isolates of M tuberculosis were determined by MGIT 960 and correlated with rpoB mutations. RFB MICs ranged from 0.125 to 0.25 µg/ml in the 34 test isolates thereby confirming phenotypic susceptibility as per critical concentration (CC) of 0.5 µg/ml. The corresponding RIF MICs ranged between 5 and 15 µg/ml, which is well above the CC of 1.0 µg/ml. Molecular-based drug susceptibility testing provides important pharmacogenetic insight by demonstrating a direct correlation between defined rpoB mutation and the level of RFB susceptibility. We suggest that isolates with marginally reduced susceptibility as compared to the epidemiological cut-off for wild-type strains (0.064 µg/ml), but lower than the current CC (≤0.5 µg/ml), are categorised as intermediate. Two breakpoints (0.064 µg/ml and 0.5 µg/ml) are recommended to distinguish between susceptible, intermediate and RFB resistant strains. This concept may assist clinicians and policy makers to make objective therapeutic decisions, especially in situations where therapeutic options are limited. The use of RFB in the ECP may improve therapeutic success and consequently minimise the risk of ongoing transmission of drug resistant M. tuberculosis strains.
- Published
- 2013
30. embB306 mutations as molecular indicators to predict ethambutol susceptibility in Mycobacterium tuberculosis
- Author
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Frederick A, Sirgel, Robin M, Warren, Elizabeth M, Streicher, Thomas C, Victor, Paul D, van Helden, and Erik C, Böttger
- Subjects
Genotype ,Drug Resistance, Bacterial ,Mutation ,Antitubercular Agents ,Humans ,Tuberculosis ,Microbial Sensitivity Tests ,Mycobacterium tuberculosis ,Ethambutol - Abstract
Discordant results in conventional susceptibility testing of ethambutol against Mycobacterium tuberculosis may lead to underreporting of drug resistance.A 240-bp region of the embB gene in 111 clinical isolates of M. tuberculosis was sequenced and examined for mutations linked to ethambutol resistance. The phenotypic susceptibility levels of the isolates were quantified by the BACTEC™ MGIT 960™ TB System and correlated with the genotypic test results. These data were analyzed to find information that could be used to clarify discordant ethambutol susceptibility test results.Mutations M306I (n = 56), M306V (n = 18) and M306L (n = 3) in M. tuberculosis showed decreased susceptibility to ethambutol. The minimum inhibitory concentrations (MICs) in 73% (56/77) of embB306 mutants were at or just above the critical concentration (MICs, 5.0 to ≤12.5 µg/ml) of ethambutol reflecting borderline (or intermediate) resistance. Eight ethambutol-resistant isolates lacked embB mutations, probably due to mutational alterations elsewhere in the genome.Our findings suggest that clinical isolates containing embB306 mutations with MICs overlapping the critical concentration are associated with discordant ethambutol susceptibility test results. The clinical significance of borderline resistance in combination treatment of tuberculosis remains to be determined before alternative ethambutol breakpoints are considered.
- Published
- 2012
31. gyrA mutations and phenotypic susceptibility levels to ofloxacin and moxifloxacin in clinical isolates of Mycobacterium tuberculosis
- Author
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Erik C. Böttger, Paul D. van Helden, Frederick A. Sirgel, Robin M. Warren, Thomas C. Victor, Elizabeth M. Streicher, University of Zurich, and Sirgel, Frederick A
- Subjects
Microbiology (medical) ,Ofloxacin ,Tuberculosis ,medicine.drug_class ,Moxifloxacin ,Antitubercular Agents ,Mutation, Missense ,610 Medicine & health ,Drug resistance ,Microbial Sensitivity Tests ,Gene mutation ,Polymorphism, Single Nucleotide ,2726 Microbiology (medical) ,Microbiology ,Mycobacterium tuberculosis ,Genotype ,Drug Resistance, Bacterial ,medicine ,2736 Pharmacology (medical) ,Humans ,Pharmacology (medical) ,Pharmacology ,Aza Compounds ,biology ,10179 Institute of Medical Microbiology ,2725 Infectious Diseases ,biochemical phenomena, metabolism, and nutrition ,bacterial infections and mycoses ,Quinolone ,biology.organism_classification ,medicine.disease ,3004 Pharmacology ,Infectious Diseases ,DNA Gyrase ,Quinolines ,570 Life sciences ,medicine.drug ,Fluoroquinolones - Abstract
Objectives To compare mutations in the quinolone resistance-determining region of the gyrA gene and flanking sequences with the MICs of ofloxacin and moxifloxacin for Mycobacterium tuberculosis. Methods The presence of mutations in 177 drug-resistant M. tuberculosis isolates was determined by DNA sequencing and the MICs quantified by MGIT 960. Results Single nucleotide polymorphisms were detected at codons 94 (n = 30), 90 (n = 12), 91 (n = 3), 89 (n = 1), 88 (n = 1) and 80 (n = 1). Four isolates with double mutations D94G plus A90V (n = 2) and D94G plus D94N (n = 2) reflect mixed populations. Agreement between genotypic and phenotypic susceptibility was high (≥97%) for both drugs. Mutant isolates had an MIC(50) of 8.0 mg/L and an MIC(90) of >10 mg/L for ofloxacin compared with an MIC(50) and MIC(90) of 2.0 mg/L for moxifloxacin. Codons 94 and 88 were linked to higher levels of fluoroquinolone resistance compared with codons 90, 91 and 89. The MIC distributions for the wild-type isolates ranged from ≤0.5 to 2.0 mg/L for ofloxacin and from ≤0.125 to 0.25 mg/L for moxifloxacin. However, 96% of the isolates with genetic alterations had MICs ≤2.0 mg/L for moxifloxacin, which is within its achievable serum levels. Conclusions This study provides quantitative evidence that the addition of moxifloxacin to extensively drug-resistant tuberculosis (XDR-TB) regimens based on a clinical breakpoint of 2.0 mg/L has merit. The use of moxifloxacin in the treatment of multidrug-resistant tuberculosis may prevent the acquisition of additional mutations and development of XDR-TB.
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- 2012
32. Mutations in the rrs A1401G gene and phenotypic resistance to amikacin and capreomycin in Mycobacterium tuberculosis
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Elizabeth M. Streicher, Erik C. Böttger, Marisa Tait, Frederick A. Sirgel, Paul D. van Helden, Robin M. Warren, Andre Trollip, Cindy Hayes, E Hoosain, Mamisa Chabula-Nxiweni, Nicolaas C. Gey van Pittius, Thomas C. Victor, and Gerrit Coetzee
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Microbiology (medical) ,Capreomycin ,Immunology ,Antitubercular Agents ,Drug resistance ,Microbial Sensitivity Tests ,Gene mutation ,Biology ,Microbiology ,Polymerase Chain Reaction ,Mycobacterium tuberculosis ,Minimum inhibitory concentration ,South Africa ,Bacterial Proteins ,Drug Resistance, Multiple, Bacterial ,RNA, Ribosomal, 16S ,Tuberculosis, Multidrug-Resistant ,medicine ,Amikacin ,Pharmacology ,Extensively drug-resistant tuberculosis ,Kanamycin ,Sequence Analysis, DNA ,medicine.disease ,biology.organism_classification ,Phenotype ,Mutation ,medicine.drug - Abstract
The aminoglycosides amikacin (AMK)/kanamycin (KAN) and the cyclic polypeptide capreomycin (CAP) are important injectable drugs in the treatment of multidrug-resistant tuberculosis. Cross-resistance among these drug classes occurs and information on the minimum inhibitory concentrations (MICs), above the normal wild-type distribution, may be useful in identifying isolates that are still accessible to drug treatment. Isolates from the Eastern Cape Province of South Africa were subjected to DNA sequencing of the rrs (1400-1500 region) and tlyA genes. Sequencing data were compared with (i) conventional susceptibility testing at standard critical concentrations (CCs) on Middlebrook 7H11 agar and (ii) MGIT 960-based MIC determinations to assess the presence of AMK- and CAP-resistant mutants. Isolates with an rrs A1401G mutation showed high-level resistance to AMK (20 mg/L) and decreased phenotypic susceptibility to CAP (MICs 10-15 mg/L). The MICs of CAP were below the bioavailability of the drug, which suggests that it may still be effective against multi- or extensively drug resistant tuberculosis [M(X)DR-TB]. Agar-based CC testing was found to be unreliable for resistance recognition of CAP in particular.
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- 2011
33. The early bactericidal activity of rifabutin in patients with pulmonary tuberculosis measured by sputum viable counts: a new method of drug assessment
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Frederik J. H. Botha, Bernard W. Van de Wal, Denis A. Mitchison, Peter K. Clark, D P Parkin, Frederick A. Sirgel, and Peter R. Donald
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Adult ,Male ,Microbiology (medical) ,medicine.medical_specialty ,Time Factors ,Rifabutin ,Adolescent ,medicine.medical_treatment ,Colony Count, Microbial ,Microbial Sensitivity Tests ,Gastroenterology ,Mycobacterium tuberculosis ,Internal medicine ,parasitic diseases ,Isoniazid ,medicine ,Humans ,Potency ,Pharmacology (medical) ,Tuberculosis, Pulmonary ,Antibacterial agent ,Pharmacology ,Chemotherapy ,biology ,business.industry ,Sputum ,biology.organism_classification ,Infectious Diseases ,Immunology ,Female ,Rifampin ,medicine.symptom ,business ,Rifampicin ,medicine.drug - Abstract
The activity of rifabutin and rifampicin against rapidly growing, extra-cellular Mycobacterium tuberculosis in cavity walls was measured by counting colony-forming units (cfu) in the sputum of 74 patients with newly diagnosed, severe pulmonary tuberculosis during the first 2 days of daily chemotherapy. The fall in counts, (log10 cfu/mL sputum/day), was termed the early bactericidal activity (EBA). The EBA, a highly reproducible measure within groups of 10-13 patients, was -0.015 for a low EBA reference group (who received no chemotherapy) and 0.495 for a high EBA reference group (who received 300 mg isoniazid daily). The EBAs in patients receiving 300 and 600 mg rifabutin were 0.014 and 0.075, and for those taking 150, 300 and 600 mg rifampicin 0.021, 0.150 and 0.204, respectively. Weight-for-weight, the ratio rifabutin to rifampicin producing the same EBA was estimated to be 2.73 (95% confidence limits 1.96-3.78). Determination of the EBA is a rapid and economical method of comparing the potency in human lesions of drugs of the same type before embarking on a conventional clinical trial.
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- 1993
34. Measuring minimum inhibitory concentrations in mycobacteria
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Frederick A, Sirgel, Ian J F, Wiid, and Paul D, van Helden
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Humans ,Tuberculosis ,Microbial Sensitivity Tests ,Mycobacterium tuberculosis ,Antibiotics, Antitubercular - Abstract
An agar dilution method for measuring minimum inhibitory concentrations (MICs) of Mycobacterium tuberculosis, based on the method of proportion, is described. Mycobacterium strains are grown on Middlebrook 7H10 (or 7H11) agar medium with twofold serially diluted drug concentrations in order to determine specific inhibitory values. The proportion of bacilli resistant to a given drug is determined by comparing the number of colony-forming units (CFU) on a drug-free control with those growing in the presence of drug within a specific concentration range. The MIC is defined as the lowest drug concentration that inhibits growth of more than 99% of a bacterial population of M. tuberculosis on solid Middlebrook medium within 21 days of incubation at 37 degrees C. The proportion method, the absolute concentration method, and the resistant ratio method have traditionally been used as standard procedures for antimycobacterial drug-susceptibility testing (DST), and reference data are mainly based on these methods. DST concepts and alternative procedures that have been adopted for DST are also briefly discussed.
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- 2010
35. Measuring Minimum Inhibitory Concentrations in Mycobacteria
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Frederick A. Sirgel, Paul D. van Helden, and Ian Wiid
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Bacilli ,Tuberculosis ,Chromatography ,biology ,medicine.drug_class ,Antibiotics ,medicine.disease ,Antimycobacterial ,biology.organism_classification ,Microbiology ,Mycobacterium tuberculosis ,Agar plate ,medicine ,Incubation ,Mycobacterium - Abstract
An agar dilution method for measuring minimum inhibitory concentrations (MICs) of Mycobacterium tuberculosis, based on the method of proportion, is described. Mycobacterium strains are grown on Middlebrook 7H10 (or 7H11) agar medium with twofold serially diluted drug concentrations in order to determine specific inhibitory values. The proportion of bacilli resistant to a given drug is determined by comparing the number of colony-forming units (CFU) on a drug-free control with those growing in the presence of drug within a specific concentration range. The MIC is defined as the lowest drug concentration that inhibits growth of more than 99% of a bacterial population of M. tuberculosis on solid Middlebrook medium within 21 days of incubation at 37 degrees C. The proportion method, the absolute concentration method, and the resistant ratio method have traditionally been used as standard procedures for antimycobacterial drug-susceptibility testing (DST), and reference data are mainly based on these methods. DST concepts and alternative procedures that have been adopted for DST are also briefly discussed.
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- 2009
36. Correction: The Rationale for Using Rifabutin in the Treatment of MDR and XDR Tuberculosis Outbreaks
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Robin M. Warren, Paul D. van Helden, Frederick A. Sirgel, Erik C. Böttger, Thomas C. Victor, and Marisa Klopper
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Multidisciplinary ,Rifabutin ,Tuberculosis ,business.industry ,lcsh:R ,lcsh:Medicine ,Outbreak ,medicine.disease ,Virology ,Relative resistance ,Mutation (genetic algorithm) ,medicine ,lcsh:Q ,lcsh:Science ,business ,Rifampicin ,medicine.drug - Abstract
There is an error in Table 1. An AspTyr mutation is wrongly abbreviated as D516T (1). It should be listed as D516Y (1). Please see the corrected Table 1 here. Table 1 MICs and relative resistance of rifampicin and rifabutin in M. tuberculosis.
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- 2015
37. Novel katG mutations causing isoniazid resistance in clinical M. tuberculosis isolates
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Antonino Catanzaro, Thomas C. Victor, Elizabeth M. Streicher, Victoria Zadorozhny, Afif Elghraoui, Camilla Rodrigues, Amy P Goodmanson, Frederick A. Sirgel, Ashu Chawla, Jessica N Torres, Anu Amallraja, Faramarz Valafar, Timothy C. Rodwell, Sarah M Ramirez-Busby, Valeru Crudu, Maria Tarcela Gler, Lynthia V. Paul, and Donald G. Catanzaro
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Silent mutation ,Sanger sequencing ,Epidemiology ,Immunology ,Antitubercular Agents ,MDR-TB ,Drug resistance ,Microbial Sensitivity Tests ,medicine.disease_cause ,Microbiology ,Mycobacterium tuberculosis ,03 medical and health sciences ,Bacterial Proteins ,Virology ,Drug Discovery ,Drug Resistance, Bacterial ,medicine ,Isoniazid ,isoniazid drug-resistance ,Humans ,Promoter Regions, Genetic ,030304 developmental biology ,Genetics ,0303 health sciences ,Mutation ,biology ,030306 microbiology ,INHA ,Point mutation ,Pyrosequencing ,General Medicine ,biology.organism_classification ,Molecular diagnostics ,bacterial infections and mycoses ,Catalase ,3. Good health ,Infectious Diseases ,tuberculosis ,whole-genome sequencing ,katG ,Parasitology ,Original Article ,novel mutation ,Oxidoreductases ,medicine.drug - Abstract
We report the discovery and confirmation of 23 novel mutations with previously undocumented role in isoniazid (INH) drug resistance, in catalase-peroxidase (katG) gene of Mycobacterium tuberculosis (Mtb) isolates. With these mutations, a synonymous mutation in fabG1 (g609a), and two canonical mutations, we were able to explain 98% of the phenotypic resistance observed in 366 clinical Mtb isolates collected from four high tuberculosis (TB)-burden countries: India, Moldova, Philippines, and South Africa. We conducted overlapping targeted and whole-genome sequencing for variant discovery in all clinical isolates with a variety of INH-resistant phenotypes. Our analysis showed that just two canonical mutations (katG 315AGC-ACC and inhA promoter-15C-T) identified 89.5% of resistance phenotypes in our collection. Inclusion of the 23 novel mutations reported here, and the previously documented point mutation in fabG1, increased the sensitivity of these mutations as markers of INH resistance to 98%. Only six (2%) of the 332 resistant isolates in our collection did not harbor one or more of these mutations. The third most prevalent substitution, at inhA promoter position -8, present in 39 resistant isolates, was of no diagnostic significance since it always co-occurred with katG 315. 79% of our isolates harboring novel mutations belong to genetic group 1 indicating a higher tendency for this group to go down an uncommon evolutionary path and evade molecular diagnostics. The results of this study contribute to our understanding of the mechanisms of INH resistance in Mtb isolates that lack the canonical mutations and could improve the sensitivity of next generation molecular diagnostics.
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- 2015
38. Front & Back Matter
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V. Mari, Tetsu Hayashida, J.G.M. Costa, A.A.F. Saraiva, Thomas C. Victor, Maiko Takahashi, Tomohisa Baba, Kate Burbury, Shinji Meda, H. Senellart, S.R. Tintino, Shigeru Komatsu, Cheng-Jen Ma, G.M.M. Guedes, Takeshi Shinohara, A.J. Carrillo-Muñoz, Jane Li, A.C. Mamede, Sachiko Matsuda, Shigemichi Hirose, A.C. Gonçalves, Hiromitsu Jinno, C.E. Sobral-Souza, J. Casalta-Lopes, A.R. Gomes, Takashi Ogura, F. Rojas, Brigitte Stöhr, Paul D. van Helden, Hannes Steiner, Deng-Chyang Wu, E. Francois, Amit Khot, C. Michel, Michael A. Savin, Noboru Nakata, Robin M. Warren, J.Y. Douillard, Isamu Matsunaga, K.K.A. Santos, A.M. Abrantes, I-Chen Wu, M.F. Botelho, A.B. Sarmento-Ribeiro, Tadashi Ikeda, E. Chamorey, Ming-Feng Hou, P. Follana, Satz Mengensatzproduktion, G. Giusiano, Yuko Kitagawa, Erik C. Böttger, Ryuichi Nishihira, M.C. Etienne-Grimaldi, M.F.B. Morais-Braga, H.D.M. Coutinho, A.F. Brito, C. Tur-Tur, Frederick A. Sirgel, J.G. Tralhão, D. Cárdenes, Chien-Yu Lu, N. Renée, Renate Pichler, Michael D. Green, Bing-Bing Yang, G. Milano, Elizabeth M. Streicher, Nagatoshi Fujiwara, Yung-Sung Yeh, Hsiang-Lin Tsai, C. Pinto-Costa, J. Bennouna, Jaw-Yuan Wang, Wolfgang Horninger, Eri Hagiwara, Nicolai Leonhartsberger, Druck Reinhardt Druck Basel, T.M. Souza, and J.C. Andrade
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Pharmacology ,Infectious Diseases ,Optics ,Oncology ,business.industry ,Drug Discovery ,Pharmacology (medical) ,General Medicine ,business ,Geology ,Front (military) - Published
- 2012
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