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O'Toole RF. Antibiotic resistance acquisition versus primary transmission in the presentation of extensively drug-resistant tuberculosis. Int J Mycobacteriol 2022; 11:343-348. [PMID: 36510916 DOI: 10.4103/ijmy.ijmy_187_22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Mycobacterium tuberculosis is the leading cause of mortality worldwide due to a single bacterial pathogen. Of concern is the negative impact that the COVID-19 pandemic has had on the control of tuberculosis (TB) including drug-resistant forms of the disease. Antimicrobial resistance increases the likelihood of worsened outcomes in TB patients including treatment failure and death. Multidrug-resistant (MDR) strains, resistant to first-line drugs isoniazid and rifampin, and extensively drug-resistant (XDR) strains with further resistance to second-line drugs (SLD), threaten control programs designed to lower TB incidence and end the disease as a public health challenge by 2030, in accordance with UN Sustainable Development Goals. Tackling TB requires an understanding of the pathways through which drug resistance emerges. Here, the roles of acquired resistance mutation, and primary transmission, are examined with regard to XDR-TB. It is apparent that XDR-TB can emerge from MDR-TB through a small number of additional resistance mutations that occur in patients undergoing drug treatment. Rapid detection of resistance, to first-line drugs and SLD, at the initiation of and during treatment, and prompt adjustment of regimens are required to ensure treatment success in these patients. Primary transmission is predicted to make an increasing contribution to the XDR-TB caseload in the future. Much work is required to improve the implementation of the World Health Organization-recommended infection control practices and block onward transmission of XDR-TB patients to contacts including health-care workers. Finally, limiting background resistance to fluoroquinolones in pre-XDR strains of M. tuberculosis will necessitate better antimicrobial stewardship in the broader use of this drug class.
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Affiliation(s)
- Ronan Francis O'Toole
- Department of Biomedicine and Medical Diagnostics, School of Science, Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand
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2
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The Neglected Contribution of Streptomycin to the Tuberculosis Drug Resistance Problem. Genes (Basel) 2021; 12:genes12122003. [PMID: 34946952 PMCID: PMC8701281 DOI: 10.3390/genes12122003] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2021] [Revised: 12/14/2021] [Accepted: 12/15/2021] [Indexed: 12/22/2022] Open
Abstract
The airborne pathogen Mycobacterium tuberculosis is responsible for a present major public health problem worsened by the emergence of drug resistance. M. tuberculosis has acquired and developed streptomycin (STR) resistance mechanisms that have been maintained and transmitted in the population over the last decades. Indeed, STR resistant mutations are frequently identified across the main M. tuberculosis lineages that cause tuberculosis outbreaks worldwide. The spread of STR resistance is likely related to the low impact of the most frequent underlying mutations on the fitness of the bacteria. The withdrawal of STR from the first-line treatment of tuberculosis potentially lowered the importance of studying STR resistance. However, the prevalence of STR resistance remains very high, could be underestimated by current genotypic methods, and was found in outbreaks of multi-drug (MDR) and extensively drug (XDR) strains in different geographic regions. Therefore, the contribution of STR resistance to the problem of tuberculosis drug resistance should not be neglected. Here, we review the impact of STR resistance and detail well-known and novel candidate STR resistance mechanisms, genes, and mutations. In addition, we aim to provide insights into the possible role of STR resistance in the development of multi-drug resistant tuberculosis.
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Rodríguez-Beltrán É, López GD, Anzola JM, Rodríguez-Castillo JG, Carazzone C, Murcia MI. Heterogeneous fitness landscape cues, pknG low expression, and phthiocerol dimycocerosate low production of Mycobacterium tuberculosis ATCC25618 rpoB S450L in enriched broth. Tuberculosis (Edinb) 2021; 132:102156. [PMID: 34891037 DOI: 10.1016/j.tube.2021.102156] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2021] [Revised: 11/23/2021] [Accepted: 11/26/2021] [Indexed: 10/19/2022]
Abstract
Multidrug-resistant tuberculosis (isoniazid/rifampin[RIF]-resistant TB) ravages developing countries. Fitness is critical in clinical outcomes. Previous studies on RIF-resistant TB (RR-TB) showed competitive fitness gains and losses, with rpoB-S450L as the most isolated/fit mutation. This study measured virulence/resistance genes, phthiocerol dimycocerosate (PDIM) levels and their relationship with rpoB S450L ATCC25618 RR-TB strain fitness. After obtaining 10 different RR-TB GenoType MTBDRplus 2.0-genotyped isolates (with nontyped, S441, H445 and S450 positions), only one S450L isolate (R9, rpoB-S450L ATCC 25618, RR 1 μg/mL) was observed, with H445Y being the most common. A competitive fitness in vitro assay with wild-type (wt) ATCC 25618: R9 1:1 in 50 mL Middlebrook 7H9/OADC was performed, and generation time (G) in vitro and relative fitness were obtained. mRNA and PDIM were extracted on log and stationary phases. Fitness decreased in rpoB S450L and H445Y strains, with heterogeneous fitness cues in three biological replicas of rpoB-S450L: one high and two low fitness replicas. S450L strain had significant pknG increase. Compared with S450L, wt-rpoB showed increased polyketide synthase ppsA expression and high PDIM peak measured by HPLC-MS in log phase compared to S450L. This contrasts with previously increased PDIM in other RR-TB isolates.
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Affiliation(s)
- Édgar Rodríguez-Beltrán
- MicobacUN Group, Microbiology Department, The National University of Colombia (NUC) School of Medicine, AV CR 30 45-03, Bogotá, D.C, 111321, Colombia
| | - Gerson-Dirceu López
- Laboratory of Advanced Analytical Techniques in Natural Products (LATNAP), Chemistry Department, Universidad de los Andes, CR 1 18A-12, Bogotá, D.C, 111711, Colombia
| | - Juan Manuel Anzola
- Corpogen, CR 4 20-41, Bogotá, D.C, 110311, Colombia; Universidad Central, CR 5 21-38, Bogotá, D.C, 110311, Colombia
| | - Juan Germán Rodríguez-Castillo
- MicobacUN Group, Microbiology Department, The National University of Colombia (NUC) School of Medicine, AV CR 30 45-03, Bogotá, D.C, 111321, Colombia
| | - Chiara Carazzone
- Laboratory of Advanced Analytical Techniques in Natural Products (LATNAP), Chemistry Department, Universidad de los Andes, CR 1 18A-12, Bogotá, D.C, 111711, Colombia
| | - Martha I Murcia
- MicobacUN Group, Microbiology Department, The National University of Colombia (NUC) School of Medicine, AV CR 30 45-03, Bogotá, D.C, 111321, Colombia.
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Quantifying transmission fitness costs of multi-drug resistant tuberculosis. Epidemics 2021; 36:100471. [PMID: 34256273 DOI: 10.1016/j.epidem.2021.100471] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2019] [Revised: 01/14/2020] [Accepted: 05/17/2021] [Indexed: 11/22/2022] Open
Abstract
As multi-drug resistant tuberculosis (MDR-TB) continues to spread, investigating the transmission potential of different drug-resistant strains becomes an ever more pressing topic in public health. While phylogenetic and transmission tree inferences provide valuable insight into possible transmission chains, phylodynamic inference combines evolutionary and epidemiological analyses to estimate the parameters of the underlying epidemiological processes, allowing us to describe the overall dynamics of disease spread in the population. In this study, we introduce an approach to Mycobacterium tuberculosis (M. tuberculosis) phylodynamic analysis employing an existing computationally efficient model to quantify the transmission fitness costs of drug resistance with respect to drug-sensitive strains. To determine the accuracy and precision of our approach, we first perform a simulation study, mimicking the simultaneous spread of drug-sensitive and drug-resistant tuberculosis (TB) strains. We analyse the simulated transmission trees using the phylodynamic multi-type birth-death model (MTBD, (Kühnert et al., 2016)) within the BEAST2 framework and show that this model can estimate the parameters of the epidemic well, despite the simplifying assumptions that MTBD makes compared to the complex TB transmission dynamics used for simulation. We then apply the MTBD model to an M. tuberculosis lineage 4 dataset that primarily consists of MDR sequences. Some of the MDR strains additionally exhibit resistance to pyrazinamide - an important first-line anti-tuberculosis drug. Our results support the previously proposed hypothesis that pyrazinamide resistance confers a transmission fitness cost to the bacterium, which we quantify for the given dataset. Importantly, our sensitivity analyses show that the estimates are robust to different prior distributions on the resistance acquisition rate, but are affected by the size of the dataset - i.e. we estimate a higher fitness cost when using fewer sequences for analysis. Overall, we propose that MTBD can be used to quantify the transmission fitness cost for a wide range of pathogens where the strains can be appropriately divided into two or more categories with distinct properties.
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Alame Emane AK, Guo X, Takiff HE, Liu S. Drug resistance, fitness and compensatory mutations in Mycobacterium tuberculosis. Tuberculosis (Edinb) 2021; 129:102091. [PMID: 34090078 DOI: 10.1016/j.tube.2021.102091] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 05/11/2021] [Accepted: 05/17/2021] [Indexed: 01/26/2023]
Abstract
For tuberculosis to be eradicated, the transmission of Multi-Drug-Resistant and eXtensively Drug Resistant strains of Mycobacterium tuberculosis (MDR and XDR-TB) must be considerably reduced. Drug resistant strains were initially thought to have reduced fitness, and the majority of resistant strains may actually have compromised fitness because they are found in only one or a few patients. In contrast, some MDR/XDR-TB strains are highly transmitted and cause large outbreaks. Most antibiotics target essential bacterial functions and the mutations that confer resistance to anti-TB drugs can incur fitness costs manifested as slower growth and reduced viability. The fitness costs vary with different resistance mutations and the bacilli can also accumulate secondary mutations that compensate for the compromised functions and partially or fully restore lost fitness. The compensatory mutations (CM) are different for each antibiotic, as they mitigate the deleterious effects of the specific functions compromised by the resistance mutations. CM are generally more common in strains with resistance mutations incurring the greatest fitness costs, but for RIF resistance, CM are most frequent in strains with the mutation carrying the least fitness cost, Ser450Leu. Here, we review what is known about fitness costs, CM and mechanisms of resistance to the drugs that define a strain as MDR or XDR-TB. The relative fitness costs of the resistance mutations and the mitigating effects of CM largely explain why certain mutations are frequently found in highly transmitted clusters while others are less frequently, rarely or never found in clinical isolates. The CM illustrate how drug resistance affects bacteria and how bacteria evolve to overcome the effects of the antibiotics, and thus a paradigm for how mycobacteria can evolve in response to stress.
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Affiliation(s)
- Amel Kevin Alame Emane
- Shenzhen Nanshan Center for Chronic Disease Control, Shenzhen, China. 7 Huaming Road, Nanshan, Shenzhen City, Guangdong Province, China
| | - Xujun Guo
- Shenzhen Nanshan Center for Chronic Disease Control, Shenzhen, China. 7 Huaming Road, Nanshan, Shenzhen City, Guangdong Province, China
| | - Howard E Takiff
- Shenzhen Nanshan Center for Chronic Disease Control, Shenzhen, China. 7 Huaming Road, Nanshan, Shenzhen City, Guangdong Province, China; Integrated Mycobacterial Pathogenomics Unit, Institut Pasteur, 28 Rue du Dr Roux, Paris, 75015, France; CMBC, Instituto Venezolano de Investigaciones Científicas, IVIC, Caracas, Venezuela.
| | - Shengyuan Liu
- Shenzhen Nanshan Center for Chronic Disease Control, Shenzhen, China. 7 Huaming Road, Nanshan, Shenzhen City, Guangdong Province, China.
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Becerra MC, Huang CC, Lecca L, Bayona J, Contreras C, Calderon R, Yataco R, Galea J, Zhang Z, Atwood S, Cohen T, Mitnick CD, Farmer P, Murray M. Transmissibility and potential for disease progression of drug resistant Mycobacterium tuberculosis: prospective cohort study. BMJ 2019; 367:l5894. [PMID: 31649017 PMCID: PMC6812583 DOI: 10.1136/bmj.l5894] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
OBJECTIVE To measure the association between phenotypic drug resistance and the risk of tuberculosis infection and disease among household contacts of patients with pulmonary tuberculosis. SETTING 106 district health centers in Lima, Peru between September 2009 and September 2012. DESIGN Prospective cohort study. PARTICIPANTS 10 160 household contacts of 3339 index patients with tuberculosis were classified on the basis of the drug resistance profile of the patient: 6189 were exposed to drug susceptible strains of Mycobacterium tuberculosis, 1659 to strains resistant to isoniazid or rifampicin, and 1541 to strains that were multidrug resistant (resistant to isoniazid and rifampicin). MAIN OUTCOME MEASURES Tuberculosis infection (positive tuberculin skin test) and the incidence of active disease (diagnosed by positive sputum smear or chest radiograph) after 12 months of follow-up. RESULTS Household contacts exposed to patients with multidrug resistant tuberculosis had an 8% (95% confidence interval 4% to 13%) higher risk of infection by the end of follow-up compared with household contacts of patients with drug sensitive tuberculosis. The relative hazard of incident tuberculosis disease did not differ among household contacts exposed to multidrug resistant tuberculosis and those exposed to drug sensitive tuberculosis (adjusted hazard ratio 1.28, 95% confidence interval 0.9 to 1.83). CONCLUSION Household contacts of patients with multidrug resistant tuberculosis were at higher risk of tuberculosis infection than contacts exposed to drug sensitive tuberculosis. The risk of developing tuberculosis disease did not differ among contacts in both groups. The evidence invites guideline producers to take action by targeting drug resistant and drug sensitive tuberculosis, such as early detection and effective treatment of infection and disease. TRIAL REGISTRATION ClinicalTrials.gov NCT00676754.
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Affiliation(s)
- Mercedes C Becerra
- Department of Global Health and Social Medicine, Harvard Medical School, 641 Huntington Avenue, Boston, MA 02115, USA
| | - Chuan-Chin Huang
- Division of Global Health Equity, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
| | | | | | | | | | | | - Jerome Galea
- School of Social Work, College of Behavioral and Community Sciences, University of South Florida, Tampa, FL, USA
| | - Zibiao Zhang
- Division of Global Health Equity, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
| | - Sidney Atwood
- Division of Global Health Equity, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
| | - Ted Cohen
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT, USA
| | - Carole D Mitnick
- Department of Global Health and Social Medicine, Harvard Medical School, 641 Huntington Avenue, Boston, MA 02115, USA
| | - Paul Farmer
- Department of Global Health and Social Medicine, Harvard Medical School, 641 Huntington Avenue, Boston, MA 02115, USA
- Division of Global Health Equity, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
| | - Megan Murray
- Department of Global Health and Social Medicine, Harvard Medical School, 641 Huntington Avenue, Boston, MA 02115, USA
- Division of Global Health Equity, Department of Medicine, Brigham and Women's Hospital, Boston, MA, USA
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Pienaar E. Multifidelity Analysis for Predicting Rare Events in Stochastic Computational Models of Complex Biological Systems. Biomed Eng Comput Biol 2018; 9:1179597218790253. [PMID: 30090024 PMCID: PMC6077899 DOI: 10.1177/1179597218790253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2018] [Accepted: 06/15/2018] [Indexed: 11/17/2022] Open
Abstract
Rare events such as genetic mutations or cell-cell interactions are important contributors to dynamics in complex biological systems, eg, in drug-resistant infections. Computational approaches can help analyze rare events that are difficult to study experimentally. However, analyzing the frequency and dynamics of rare events in computational models can also be challenging due to high computational resource demands, especially for high-fidelity stochastic computational models. To facilitate analysis of rare events in complex biological systems, we present a multifidelity analysis approach that uses medium-fidelity analysis (Monte Carlo simulations) and/or low-fidelity analysis (Markov chain models) to analyze high-fidelity stochastic model results. Medium-fidelity analysis can produce large numbers of possible rare event trajectories for a single high-fidelity model simulation. This allows prediction of both rare event dynamics and probability distributions at much lower frequencies than high-fidelity models. Low-fidelity analysis can calculate probability distributions for rare events over time for any frequency by updating the probabilities of the rare event state space after each discrete event of the high-fidelity model. To validate the approach, we apply multifidelity analysis to a high-fidelity model of tuberculosis disease. We validate the method against high-fidelity model results and illustrate the application of multifidelity analysis in predicting rare event trajectories, performing sensitivity analyses and extrapolating predictions to very low frequencies in complex systems. We believe that our approach will complement ongoing efforts to enable accurate prediction of rare event dynamics in high-fidelity computational models.
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Affiliation(s)
- Elsje Pienaar
- Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, USA
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Pienaar E, Linderman JJ, Kirschner DE. Emergence and selection of isoniazid and rifampin resistance in tuberculosis granulomas. PLoS One 2018; 13:e0196322. [PMID: 29746491 PMCID: PMC5944939 DOI: 10.1371/journal.pone.0196322] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2017] [Accepted: 04/11/2018] [Indexed: 12/15/2022] Open
Abstract
Drug resistant tuberculosis is increasing world-wide. Resistance against isoniazid (INH), rifampicin (RIF), or both (multi-drug resistant TB, MDR-TB) is of particular concern, since INH and RIF form part of the standard regimen for TB disease. While it is known that suboptimal treatment can lead to resistance, it remains unclear how host immune responses and antibiotic dynamics within granulomas (sites of infection) affect emergence and selection of drug-resistant bacteria. We take a systems pharmacology approach to explore resistance dynamics within granulomas. We integrate spatio-temporal host immunity, INH and RIF dynamics, and bacterial dynamics (including fitness costs and compensatory mutations) in a computational framework. We simulate resistance emergence in the absence of treatment, as well as resistance selection during INH and/or RIF treatment. There are four main findings. First, in the absence of treatment, the percentage of granulomas containing resistant bacteria mirrors the non-monotonic bacterial dynamics within granulomas. Second, drug-resistant bacteria are less frequently found in non-replicating states in caseum, compared to drug-sensitive bacteria. Third, due to a steeper dose response curve and faster plasma clearance of INH compared to RIF, INH-resistant bacteria have a stronger influence on treatment outcomes than RIF-resistant bacteria. Finally, under combination therapy with INH and RIF, few MDR bacteria are able to significantly affect treatment outcomes. Overall, our approach allows drug-specific prediction of drug resistance emergence and selection in the complex granuloma context. Since our predictions are based on pre-clinical data, our approach can be implemented relatively early in the treatment development process, thereby enabling pro-active rather than reactive responses to emerging drug resistance for new drugs. Furthermore, this quantitative and drug-specific approach can help identify drug-specific properties that influence resistance and use this information to design treatment regimens that minimize resistance selection and expand the useful life-span of new antibiotics.
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Affiliation(s)
- Elsje Pienaar
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Jennifer J. Linderman
- Department of Chemical Engineering, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Denise E. Kirschner
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, United States of America
- * E-mail:
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Al-Saeedi M, Al-Hajoj S. Diversity and evolution of drug resistance mechanisms in Mycobacterium tuberculosis. Infect Drug Resist 2017; 10:333-342. [PMID: 29075131 PMCID: PMC5648319 DOI: 10.2147/idr.s144446] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Despite the efficacy of antibiotics to protect humankind against many deadly pathogens, such as Mycobacterium tuberculosis, nothing can prevent the emergence of drug-resistant strains. Several mechanisms facilitate drug resistance in M. tuberculosis including compensatory evolution, epistasis, clonal interference, cell wall integrity, efflux pumps, and target mimicry. In this study, we present recent findings relevant to these mechanisms, which can enable the discovery of new drug targets and subsequent development of novel drugs for treatment of drug-resistant M. tuberculosis.
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Affiliation(s)
- Mashael Al-Saeedi
- Department of Infection and Immunity, Mycobacteriology Research Section, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
| | - Sahal Al-Hajoj
- Department of Infection and Immunity, Mycobacteriology Research Section, King Faisal Specialist Hospital and Research Center, Riyadh, Saudi Arabia
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Knight GM, Colijn C, Shrestha S, Fofana M, Cobelens F, White RG, Dowdy DW, Cohen T. The Distribution of Fitness Costs of Resistance-Conferring Mutations Is a Key Determinant for the Future Burden of Drug-Resistant Tuberculosis: A Model-Based Analysis. Clin Infect Dis 2016; 61Suppl 3:S147-54. [PMID: 26409276 DOI: 10.1093/cid/civ579] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
BACKGROUND Drug resistance poses a serious challenge for the control of tuberculosis in many settings. It is well established that the expected future trend in resistance depends on the reproductive fitness of drug-resistant Mycobacterium tuberculosis. However, the variability in fitness between strains with different resistance-conferring mutations has been largely ignored when making these predictions. METHODS We developed a novel approach for incorporating the variable fitness costs of drug resistance-conferring mutations and for tracking this distribution of fitness costs over time within a transmission model. We used this approach to describe the effects of realistic fitness cost distributions on the future prevalence of drug-resistant tuberculosis. RESULTS The shape of the distribution of fitness costs was a strong predictor of the long-term prevalence of resistance. While, as expected, lower average fitness costs of drug resistance-conferring mutations were associated with more severe epidemics of drug-resistant tuberculosis, fitness distributions with greater variance also led to higher levels of drug resistance. For example, compared to simulations in which the fitness cost of resistance was fixed, introducing a realistic amount of variance resulted in a 40% increase in prevalence of drug-resistant tuberculosis after 20 years. CONCLUSIONS The differences in the fitness costs associated with drug resistance-conferring mutations are a key determinant of the future burden of drug-resistant tuberculosis. Future studies that can better establish the range of fitness costs associated with drug resistance-conferring mutations will improve projections and thus facilitate better public health planning efforts.
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Affiliation(s)
- Gwenan M Knight
- Tuberculosis Modelling Group, Centre for the Mathematical Modelling of Infectious Diseases, Tuberculosis Centre, Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine
| | - Caroline Colijn
- Department of Mathematics, Imperial College London, United Kingdom
| | - Sourya Shrestha
- Department of Epidemiology, Johns Hopkins School of Public Health, Baltimore, Maryland
| | - Mariam Fofana
- Department of Epidemiology, Johns Hopkins School of Public Health, Baltimore, Maryland
| | - Frank Cobelens
- Amsterdam Institute for Global Health and Development, Academic Medical Center KNCV Tuberculosis Foundation, The Hague, The Netherlands
| | - Richard G White
- Tuberculosis Modelling Group, Centre for the Mathematical Modelling of Infectious Diseases, Tuberculosis Centre, Department of Infectious Disease Epidemiology, Faculty of Epidemiology and Public Health, London School of Hygiene and Tropical Medicine
| | - David W Dowdy
- Department of Epidemiology, Johns Hopkins School of Public Health, Baltimore, Maryland
| | - Ted Cohen
- Department of Epidemiology of Microbial Diseases, School of Public Health, Yale University, New Haven, Connecticut
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11
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Cadosch D, Abel zur Wiesch P, Kouyos R, Bonhoeffer S. The Role of Adherence and Retreatment in De Novo Emergence of MDR-TB. PLoS Comput Biol 2016; 12:e1004749. [PMID: 26967493 PMCID: PMC4788301 DOI: 10.1371/journal.pcbi.1004749] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Accepted: 01/12/2016] [Indexed: 11/19/2022] Open
Abstract
Treatment failure after therapy of pulmonary tuberculosis (TB) infections is an important challenge, especially when it coincides with de novo emergence of multi-drug-resistant TB (MDR-TB). We seek to explore possible causes why MDR-TB has been found to occur much more often in patients with a history of previous treatment. We develop a mathematical model of the replication of Mycobacterium tuberculosis within a patient reflecting the compartments of macrophages, granulomas, and open cavities as well as parameterizing the effects of drugs on the pathogen dynamics in these compartments. We use this model to study the influence of patient adherence to therapy and of common retreatment regimens on treatment outcome. As expected, the simulations show that treatment success increases with increasing adherence. However, treatment occasionally fails even under perfect adherence due to interpatient variability in pharmacological parameters. The risk of generating MDR de novo is highest between 40% and 80% adherence. Importantly, our simulations highlight the double-edged effect of retreatment: On the one hand, the recommended retreatment regimen increases the overall success rate compared to re-treating with the initial regimen. On the other hand, it increases the probability to accumulate more resistant genotypes. We conclude that treatment adherence is a key factor for a positive outcome, and that screening for resistant strains is advisable after treatment failure or relapse.
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Affiliation(s)
| | - Pia Abel zur Wiesch
- Division of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America
- Department of Pharmacy, Faculty of Health Sciences, Norwegian Arctic University (UiT), Tromsø, Norway
| | - Roger Kouyos
- Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Switzerland & Institute of Medical Virology, Swiss National Center for Retroviruses, University of Zurich, Zurich, Switzerland
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12
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Salvatore PP, Becerra MC, Abel zur Wiesch P, Hinkley T, Kaur D, Sloutsky A, Cohen T. Fitness Costs of Drug Resistance Mutations in Multidrug-Resistant Mycobacterium tuberculosis: A Household-Based Case-Control Study. J Infect Dis 2015; 213:149-55. [PMID: 26092854 DOI: 10.1093/infdis/jiv347] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 06/15/2015] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND The projected long-term prevalence of multidrug-resistant (MDR) tuberculosis depends upon the relative fitness of MDR Mycobacterium tuberculosis strains, compared with non-MDR strains. While many experimental models have tested the in vitro or in vivo fitness costs of various drug resistance mutations, fewer epidemiologic studies have attempted to validate these experimental findings. METHODS We performed a case-control study comparing drug resistance-associated mutations from MDR M. tuberculosis strains causing multiple cases in a household to matched MDR strains without evidence of secondary household cases. RESULTS Eighty-eight multiple-case and 88 single-case household MDR strains were analyzed for 10 specific drug resistance-associated polymorphisms previously associated with fitness effects. We found that the isoniazid-resistant katG Ser315Thr mutation occurred more than twice as frequently in multiple-case households than in single-case households (odds ratio [OR], 2.39; 95% confidence interval [CI], 1.21-4.70), corroborating previous experimental findings. However, strains carrying both the katG Ser315Thr mutation and the rpsL Lys43Arg mutation were less likely to be found in multiple-case households (OR, 0.09; 95% CI, .01-.73), suggesting a negative epistatic interaction which contrasts previous findings. CONCLUSIONS The case-control design presents a useful approach for assessing in vivo fitness effects of drug resistance mutations.
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Affiliation(s)
- Phillip P Salvatore
- Department of Epidemiology, Harvard School of Public Health Department of Molecular Microbiology and Immunology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland
| | | | - Pia Abel zur Wiesch
- Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut
| | - Trevor Hinkley
- Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut
| | - Devinder Kaur
- Massachusetts Supranational TB Reference Laboratory, University of Massachusetts Medical School, Boston
| | - Alexander Sloutsky
- Massachusetts Supranational TB Reference Laboratory, University of Massachusetts Medical School, Boston
| | - Ted Cohen
- Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut
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Grandjean L, Gilman RH, Martin L, Soto E, Castro B, Lopez S, Coronel J, Castillo E, Alarcon V, Lopez V, San Miguel A, Quispe N, Asencios L, Dye C, Moore DAJ. Transmission of Multidrug-Resistant and Drug-Susceptible Tuberculosis within Households: A Prospective Cohort Study. PLoS Med 2015; 12:e1001843; discussion e1001843. [PMID: 26103620 PMCID: PMC4477882 DOI: 10.1371/journal.pmed.1001843] [Citation(s) in RCA: 90] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/08/2014] [Accepted: 05/15/2015] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND The "fitness" of an infectious pathogen is defined as the ability of the pathogen to survive, reproduce, be transmitted, and cause disease. The fitness of multidrug-resistant tuberculosis (MDRTB) relative to drug-susceptible tuberculosis is cited as one of the most important determinants of MDRTB spread and epidemic size. To estimate the relative fitness of drug-resistant tuberculosis cases, we compared the incidence of tuberculosis disease among the household contacts of MDRTB index patients to that among the contacts of drug-susceptible index patients. METHODS AND FINDINGS This 3-y (2010-2013) prospective cohort household follow-up study in South Lima and Callao, Peru, measured the incidence of tuberculosis disease among 1,055 household contacts of 213 MDRTB index cases and 2,362 household contacts of 487 drug-susceptible index cases. A total of 35/1,055 (3.3%) household contacts of 213 MDRTB index cases developed tuberculosis disease, while 114/2,362 (4.8%) household contacts of 487 drug-susceptible index patients developed tuberculosis disease. The total follow-up time for drug-susceptible tuberculosis contacts was 2,620 person-years, while the total follow-up time for MDRTB contacts was 1,425 person-years. Using multivariate Cox regression to adjust for confounding variables including contact HIV status, contact age, socio-economic status, and index case sputum smear grade, the hazard ratio for tuberculosis disease among MDRTB household contacts was found to be half that for drug-susceptible contacts (hazard ratio 0.56, 95% CI 0.34-0.90, p = 0.017). The inference of transmission in this study was limited by the lack of genotyping data for household contacts. Capturing incident disease only among household contacts may also limit the extrapolation of these findings to the community setting. CONCLUSIONS The low relative fitness of MDRTB estimated by this study improves the chances of controlling drug-resistant tuberculosis. However, fitter multidrug-resistant strains that emerge over time may make this increasingly difficult.
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Affiliation(s)
- Louis Grandjean
- Wellcome Centre for Clinical Tropical Medicine, Imperial College London, London, United Kingdom
- Universidad Peruana Cayetano Heredia, Lima, Peru
- TB Centre, London School of Hygiene & Tropical Medicine, London, United Kingdom
- * E-mail:
| | - Robert H. Gilman
- Universidad Peruana Cayetano Heredia, Lima, Peru
- Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States of America
| | - Laura Martin
- Universidad Peruana Cayetano Heredia, Lima, Peru
| | - Esther Soto
- Universidad Peruana Cayetano Heredia, Lima, Peru
| | | | - Sonia Lopez
- Universidad Peruana Cayetano Heredia, Lima, Peru
| | | | - Edith Castillo
- Laboratorio de Mycobacteriologia, Dirección Regional de Salud–Región Callao, Lima, Peru
| | | | - Virginia Lopez
- Estrategia Sanitaria Nacional de Prevención y Control de la Tuberculosis and Laboratorio de Mycobacteriologia, Dirección de Salud II–Lima Sur, Lima, Peru
| | - Angela San Miguel
- Estrategia Sanitaria Nacional de Prevención y Control de la Tuberculosis and Laboratorio de Mycobacteriologia, Dirección de Salud II–Lima Sur, Lima, Peru
| | | | | | - Christopher Dye
- Office for HIV/AIDS, Malaria, Tuberculosis and Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland
| | - David A. J. Moore
- Universidad Peruana Cayetano Heredia, Lima, Peru
- TB Centre, London School of Hygiene & Tropical Medicine, London, United Kingdom
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14
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MacLean RC, Vogwill T. Limits to compensatory adaptation and the persistence of antibiotic resistance in pathogenic bacteria. EVOLUTION MEDICINE AND PUBLIC HEALTH 2014; 2015:4-12. [PMID: 25535278 PMCID: PMC4323496 DOI: 10.1093/emph/eou032] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Antibiotic resistance carries a fitness cost that could potentially limit the spread of resistance in bacterial pathogens. In spite of this cost, a large number of experimental evolution studies have found that resistance is stably maintained in the absence of antibiotics as a result of compensatory evolution. Clinical studies, on the other hand, have found that resistance in pathogen populations usually declines after antibiotic use is stopped, suggesting that compensatory adaptation is not effective in vivo. In this article, we argue that this disagreement arises because there are limits to compensatory adaptation in nature that are not captured by the design of current laboratory selection experiments. First, clinical treatment fails to eradicate antibiotic-sensitive strains, and competition between sensitive and resistant strains leads to the rapid loss of resistance following treatment. Second, laboratory studies overestimate the efficacy of compensatory adaptation in nature by failing to capture costs associated with compensatory mutations. Taken together, these ideas can potentially reconcile evolutionary theory with the clinical dynamics of antibiotic resistance and guide the development of strategies for containing resistance in clinical pathogens.
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Affiliation(s)
- R Craig MacLean
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
| | - Tom Vogwill
- Department of Zoology, University of Oxford, South Parks Road, Oxford, OX1 3PS, UK
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15
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Seddon JA, Shingadia D. Epidemiology and disease burden of tuberculosis in children: a global perspective. Infect Drug Resist 2014; 7:153-65. [PMID: 24971023 PMCID: PMC4069045 DOI: 10.2147/idr.s45090] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Our understanding of the tuberculosis (TB) epidemic in children is incomplete due to challenges in diagnosis and reporting. Children have also been largely excluded from research and advocacy. However, the tide appears to be turning and interest in pediatric TB is increasing. In this article, we explore the epidemiology of childhood TB by first reviewing the natural history of TB in children and the factors that impact on each of the stages from exposure to disease. We then discuss how these factors affect what we see at a country and regional level. Finally, we assess the burden of childhood TB globally.
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Affiliation(s)
- James A Seddon
- Department of Paediatric Infectious Diseases, Imperial College London, London, UK
| | - Delane Shingadia
- Department of Paediatric Infectious Diseases, Great Ormond Street Hospital, London, UK
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16
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Abstract
INTRODUCTION Drug-resistant tuberculosis (DR-TB) is associated with increased mortality and morbidity. This is at least partly due to late diagnosis and ineffective treatment of drug-resistant status. SOURCES OF DATA Selective search of the literature on DR-TB supplemented by recent guidelines from the World Health Organization. AREAS OF AGREEMENT Better and more rapid diagnosis of DR-TB by new techniques such as Xpert Mtb/RIF are likely to make a substantial impact on the disease. New therapeutics for DR-TB are entering, or about to enter the market for the first time in decades. AREAS OF CONTROVERSY It is not clear whether new treatments should be restricted for DR-TB or also used for drug-susceptible tuberculosis. GROWING POINTS With several new agents on the horizon, there is the real possibility of an entirely new regimen for tuberculosis. AREAS TIMELY FOR DEVELOPING RESEARCH An inexpensive 'near-patient' diagnostic test is still needed. Optimizing new drug combination regimens in a timely manner is urgently required.
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Affiliation(s)
- Melody Toosky
- Centre for Infectious Diseases Research, Tsinghua University School of Medicine, Beijing, China
| | - Babak Javid
- Centre for Infectious Diseases Research, Tsinghua University School of Medicine, Beijing, China Collaborative Innovation Center for Diagnosis and Treatment of Infectious Disease, Hangzhou, China Department of Medicine, University of Cambridge, Cambridge, UK
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17
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18
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19
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Koch A, Mizrahi V, Warner DF. The impact of drug resistance on Mycobacterium tuberculosis physiology: what can we learn from rifampicin? Emerg Microbes Infect 2014; 3:e17. [PMID: 26038512 PMCID: PMC3975073 DOI: 10.1038/emi.2014.17] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2013] [Revised: 12/12/2013] [Accepted: 12/30/2013] [Indexed: 01/08/2023]
Abstract
The emergence of drug-resistant pathogens poses a major threat to public health. Although influenced by multiple factors, high-level resistance is often associated with mutations in target-encoding or related genes. The fitness cost of these mutations is, in turn, a key determinant of the spread of drug-resistant strains. Rifampicin (RIF) is a frontline anti-tuberculosis agent that targets the rpoB-encoded β subunit of the DNA-dependent RNA polymerase (RNAP). In Mycobacterium tuberculosis (Mtb), RIF resistance (RIF(R)) maps to mutations in rpoB that are likely to impact RNAP function and, therefore, the ability of the organism to cause disease. However, while numerous studies have assessed the impact of RIF(R) on key Mtb fitness indicators in vitro, the consequences of rpoB mutations for pathogenesis remain poorly understood. Here, we examine evidence from diverse bacterial systems indicating very specific effects of rpoB polymorphisms on cellular physiology, and consider these observations in the context of Mtb. In addition, we discuss the implications of these findings for the propagation of clinically relevant RIF(R) mutations. While our focus is on RIF, we also highlight results which suggest that drug-independent effects might apply to a broad range of resistance-associated mutations, especially in an obligate pathogen increasingly linked with multidrug resistance.
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Affiliation(s)
- Anastasia Koch
- Medical Research Council/National Health Laboratory Service/University of Cape Town Molecular Mycobacteriology Research Unit, Department of Science and Technology/National Research Foundation Centre of Excellence for Biomedical Tuberculosis Research, Institute of Infectious Disease and Molecular Medicine and Department of Clinical Laboratory Sciences, University of Cape Town , Cape Town 7701, South Africa
| | - Valerie Mizrahi
- Medical Research Council/National Health Laboratory Service/University of Cape Town Molecular Mycobacteriology Research Unit, Department of Science and Technology/National Research Foundation Centre of Excellence for Biomedical Tuberculosis Research, Institute of Infectious Disease and Molecular Medicine and Department of Clinical Laboratory Sciences, University of Cape Town , Cape Town 7701, South Africa
| | - Digby F Warner
- Medical Research Council/National Health Laboratory Service/University of Cape Town Molecular Mycobacteriology Research Unit, Department of Science and Technology/National Research Foundation Centre of Excellence for Biomedical Tuberculosis Research, Institute of Infectious Disease and Molecular Medicine and Department of Clinical Laboratory Sciences, University of Cape Town , Cape Town 7701, South Africa
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20
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Müller B, Borrell S, Rose G, Gagneux S. The heterogeneous evolution of multidrug-resistant Mycobacterium tuberculosis. Trends Genet 2012; 29:160-9. [PMID: 23245857 DOI: 10.1016/j.tig.2012.11.005] [Citation(s) in RCA: 118] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Revised: 10/18/2012] [Accepted: 11/09/2012] [Indexed: 10/27/2022]
Abstract
Recent surveillance data of multidrug-resistant tuberculosis (MDR-TB) reported the highest rates of resistance ever documented. As further amplification of resistance in MDR strains of Mycobacterium tuberculosis occurs, extensively drug-resistant (XDR) and totally drug-resistant (TDR) TB are beginning to emerge. Although for the most part, the epidemiological factors involved in the spread of MDR-TB are understood, insights into the bacterial drivers of MDR-TB have been gained only recently, largely owing to novel technologies and research in other organisms. Herein, we review recent findings on how bacterial factors, such as persistence, hypermutation, the complex interrelation between drug resistance and fitness, compensatory evolution, and epistasis affect the evolution of multidrug resistance in M. tuberculosis. Improved knowledge of these factors will help better predict the future trajectory of MDR-TB, and contribute to the development of new tools and strategies to combat this growing public health threat.
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Affiliation(s)
- Borna Müller
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland
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21
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Cohen T, Dye C, Colijn C, Williams B, Murray M. Mathematical models of the epidemiology and control of drug-resistant TB. Expert Rev Respir Med 2012; 3:67-79. [PMID: 20477283 DOI: 10.1586/17476348.3.1.67] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Recent reports of extensively drug-resistant TB in South Africa have renewed concerns that antibiotic resistance may undermine progress in TB control. We review three major questions for which mathematical models elucidate the epidemiology and control of drug-resistant TB. How is multiple drug-resistant Mycobacterium tuberculosis selected for in individuals exposed to combination chemotherapy? What factors determine the prevalence of drug-resistant TB? Which interventions to prevent the spread of drug-resistant TB are effective and feasible? Models offer insight into the acquisition and amplification of drug resistance, reveal the importance of distinguishing the intrinsic and extrinsic determinants of the reproductive capacity of drug-resistant M. tuberculosis, and demonstrate the cost effectiveness of interventions for drug-resistant TB. These models also highlight knowledge gaps for which new research will improve our ability to project trends of drug resistance and develop more effective policies for its control.
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Affiliation(s)
- Ted Cohen
- Division of Global Health Equity, Brigham and Women's Hospital, Boston, MA, USA and Department of Epidemiology, Harvard School of Public Health, 677 Huntington Avenue, Boston, MA 02115, USA.
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22
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Bostanabad SZ, Shekarabei M, Nojoumi SA, Jabbarzadeh E, Ghalami M, Kazemi VM, Beigdeli MG, Karim Rahimi M, Bossak M, Sagalchyk ER, Konstantina Surkova L, Mikhaelovna Zalutska A, Slizen V, Petrovich Titov L. Study of Genetic Evolution in Mycobacterium tuberculosis Isolates from Patients with Active Pulmonary Tuberculosis in the Iran and Belarus. Open Microbiol J 2011; 5:32-42. [PMID: 21760866 PMCID: PMC3134958 DOI: 10.2174/1874285801105010032] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2011] [Revised: 04/14/2011] [Accepted: 04/16/2011] [Indexed: 11/24/2022] Open
Abstract
Objective: This is the new comparative geogenetic molecular evolution research of M. tuberculosis in Iran and Belarus. Thus, we researched the genetic patterns of samples collected in the first survey of anti-tuberculosis drug-resistance by gene coding of RNA polymerase as part of the international project of on tuberculosis. Method: DNA extraction and amplification of rpoB gene was performed. All PCR products of gene were sequenced using the Amersham auto sequencer. For analysing phenogram has been demonstrated by method UPGMA and Neighbour-Joining. Clinical isolates (70/473) were analyzed by using sequencing gene rpoB and genotyped by program DNAMAN and MEGA. Results: The all data were compared with the international database of national center for biotechnology information website. Multi drug resistant of tuberculosis patient (MDR-TB) was 92% in never treated and 8% in previously treated. Mutations in rpoB gene and katG genes were showed in 95% and 84% of the MDR isolates, respectively. Two clusters were found to be identical by the four different analysis methods, presumably representing cases of recent transmission of MDR tuberculosis. The other isolates are divided in Iran into 2 groups: group A – similar to the Eastern strains (China, Taiwan) and group B – strains of another genotype. And 3 groups in Belarus: group A - Strains of the first group are more similar to the standard European and Eastern ones China and Taiwan) which diverged in the last 10 years (Genetic evolution rate), i.e. they are relatively new ones, and that is confirmed by the mutations, group B - Strains of the second group diverged earlier; they are older than the strains of the first group (16 years old- time and rate of evolution) and group C - Strains of the third group are similar to European strains and only circulate in Brest region. They are grouped separately on the phenogram and became prevalent in Iran (they are called Iranian residential strains and also is genetic analogy between group A from Iran and Belarusian isolates. Conclusion: This research gives a first result on genetic evolution of the M. tuberculosis strains distributing in the Iran and Belarus during the first survey of anti-tuberculosis drug-resistance and is homologies between groups A from Iran with group A from Belarus. It may aid in the creation of a national database that will be a valuable support for further studies.
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23
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O'Sullivan DM, McHugh TD, Gillespie SH. Mapping the fitness of Mycobacterium tuberculosis strains: a complex picture. J Med Microbiol 2010; 59:1533-1535. [PMID: 20724506 DOI: 10.1099/jmm.0.019091-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- D M O'Sullivan
- Department of Infection, Royal Free Campus, University College London, Rowland Hill Street, Hampstead, London NW3 2PF, UK
| | - T D McHugh
- Department of Infection, Royal Free Campus, University College London, Rowland Hill Street, Hampstead, London NW3 2PF, UK
| | - S H Gillespie
- Health Protection Agency, Regional Microbiology Network, Holborn Gate, London WC1V 7PP, UK.,Department of Infection, Royal Free Campus, University College London, Rowland Hill Street, Hampstead, London NW3 2PF, UK
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24
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Low Occurrence of Tuberculosis Drug Resistance among Pulmonary Tuberculosis Patients from an Urban Setting, with a Long-Running DOTS Program in Zambia. Tuberc Res Treat 2010; 2010:938178. [PMID: 22567261 PMCID: PMC3335559 DOI: 10.1155/2010/938178] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Revised: 04/27/2010] [Accepted: 05/18/2010] [Indexed: 11/17/2022] Open
Abstract
We set out to determine the levels of Mycobacterium tuberculosis resistance to first- and second-line TB drugs in an urban population in Zambia. Sputum samples were collected consecutively from all smear-positive, new and previously treated patients, from four diagnostic centres in Ndola between January and July 2006. Drug susceptibility testing was performed using the proportion method against four first- and two second-line TB drugs. Results. Among 156 new cases, any resistance was observed to be 7.7%, monoresistance to isoniazid and rifampicin was 4.5% and 1.3%, respectively. Of 31 retreatment cases, any resistance was observed to be 16.1%, monoresistance to isoniazid and rifampicin was 3.3% for each drug, and one case of resistance to both isoniazid and rifampicin (multidrug resistance) was detected. No resistance to kanamycin or ofloxacin was detected. Conclusion. Although not representative of the country, these results show low levels of drug resistance in a community with a long-standing DOTS experience. Resource constrained countries may reduce TB drug resistance by implementing community-based strategies that enhance treatment completion.
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25
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Andersson DI, Hughes D. Antibiotic resistance and its cost: is it possible to reverse resistance? Nat Rev Microbiol 2010; 8:260-71. [PMID: 20208551 DOI: 10.1038/nrmicro2319] [Citation(s) in RCA: 1427] [Impact Index Per Article: 101.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Most antibiotic resistance mechanisms are associated with a fitness cost that is typically observed as a reduced bacterial growth rate. The magnitude of this cost is the main biological parameter that influences the rate of development of resistance, the stability of the resistance and the rate at which the resistance might decrease if antibiotic use were reduced. These findings suggest that the fitness costs of resistance will allow susceptible bacteria to outcompete resistant bacteria if the selective pressure from antibiotics is reduced. Unfortunately, the available data suggest that the rate of reversibility will be slow at the community level. Here, we review the factors that influence the fitness costs of antibiotic resistance, the ways by which bacteria can reduce these costs and the possibility of exploiting them.
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Affiliation(s)
- Dan I Andersson
- Department of Medical Biochemistry and Microbiology, Uppsala University, BOX 582, SE-751 23, Uppsala, Sweden.
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26
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Bacon J, Hatch KA, Allnutt J. Application of continuous culture for measuring the effect of environmental stress on mutation frequency in Mycobacterium tuberculosis. Methods Mol Biol 2010; 642:123-140. [PMID: 20401591 DOI: 10.1007/978-1-60327-279-7_10] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/29/2023]
Abstract
The ability of all pathogens to survive within the host is key to their success in establishing disease. Environmental conditions that affect the growth of a pathogen in the host include nutrient status, environmental pH, oxygen availability, and host defences. Studying the response of Mycobacterium tuberculosis (M. tuberculosis) exposed to these relevant host conditions in vitro will further increase our understanding of how these environments have an impact on the molecular mechanisms M. tuberculosis adopts to combat the effects of external influences such as antimycobacterials. The methods presented here are used to investigate the effect of environmental factors on the development of drug-resistant M. tuberculosis. Cultures grown under controlled conditions in continuous culture are sampled and the frequency with which resistant mutants develop are determined. These studies provide data that aid our understanding of the complex interaction between the host environment and invading bacterium that allow resistant strains to develop and continue to cause disease.
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Affiliation(s)
- Joanna Bacon
- TB Research Group, Health Protection Agency, Centre for Emergency Preparedness and Response, Salisbury, Wiltshire, UK
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27
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Abstract
Acquisition of antibiotic resistance may be associated with a physiological cost for the bacterium. Determination of growth rate and generation time is often used to measure fitness costs associated with antibiotic resistance. However, fitness costs may be small and difficult to quantify and multiple models are required. Available in vitro models that can be used to measure fitness include quantification of biofilm growth, survival in water, resistance to drying, and measurement of planktonic growth rates. The use of growth curve techniques to determine generation time is laborious, time-consuming, and can introduce sampling error. We have described the use of a semi-automated liquid culture system to estimate generation time in Burkholderia cepacia complex bacteria. We have also used the BacT/ALERT system to determine generation time and enumerate bacterial numbers in Mycobacterium tuberculosis. We describe methods for measuring biofilm growth and environmental survival in Burkholderia cepacia complex bacteria. These methods can be adapted for use with other organisms.
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28
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Singer RS, Mayer AE, Hanson TE, Isaacson RE. Do microbial interactions and cultivation media decrease the accuracy of Salmonella surveillance systems and outbreak investigations? J Food Prot 2009; 72:707-13. [PMID: 19435216 DOI: 10.4315/0362-028x-72.4.707] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Cultivation methods are commonly used in Salmonella surveillance systems and outbreak investigations, and consequently, conclusions about Salmonella evolution and transmission are highly dependent on the performance characteristics of these methods. Past studies have shown that Salmonella serotypes can exhibit different growth characteristics in the same enrichment and selective media. This could lead not only to biased conclusions about the dominant strain present in a sample with mixed Salmonella populations, but also to a low sensitivity for detecting a Salmonella strain in a sample with only a single strain present. The objective of this study was to determine whether cultivation media select preferentially for specific strains of Salmonella in heterogeneous cultures. In this study, four different Salmonella strains (one Salmonella Newport, two Salmonella Typhimurium, and one Salmonella Enteritidis) were competed in a broth-based experiment and a bovine fecal experiment with varied combinations and concentrations of each strain. In all experiments, the strain of Salmonella Newport was the most competitive, regardless of the starting concentration and cultivation protocol. One strain of Salmonella Typhimurium was rarely detected in competition, even when it was the only strain present in bovine feces. Overall, the probability of detecting a specific Salmonella strain had little to do with its starting concentration in the sample. The bias introduced by culture could be dramatically biasing Salmonella surveillance systems and hindering traceback investigations during Salmonella outbreaks. Future studies should focus on the microbiological explanations for this Salmonella interstrain variability, approaches for minimizing the bias, and estimations of the public health significance of this bias.
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Affiliation(s)
- Randall S Singer
- Department of Veterinary and Biomedical Sciences, College of Veterinary Medicine, 300A VSB, 1971 Commonwealth Avenue, University of Minnesota, St. Paul, Minnesota 55108, USA.
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29
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Colijn C, Cohen T, Murray M. Latent coinfection and the maintenance of strain diversity. Bull Math Biol 2008; 71:247-63. [PMID: 19082663 DOI: 10.1007/s11538-008-9361-y] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Accepted: 07/10/2008] [Indexed: 11/26/2022]
Abstract
Technologies for strain differentiation and typing have made it possible to detect genetic diversity of pathogens, both within individual hosts and within communities. Coinfection of a host by more than one pathogen strain may affect the relative frequency of these strains at the population level through complex within- and between-host interactions; in infectious diseases that have a long latent period, interstrain competition during latency is likely to play an important role in disease dynamics. We show that SEIR models that include a class of latently coinfected individuals can have markedly different long-term dynamics than models without coinfection, and that coinfection can greatly facilitate the stable coexistence of strains. We demonstrate these dynamics using a model relevant to tuberculosis in which people may experience latent coinfection with both drug sensitive and drug resistant strains. Using this model, we show that the existence of a latent coinfected state allows the possibility that disease control interventions that target latency may facilitate the emergence of drug resistance.
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Affiliation(s)
- Caroline Colijn
- Department of Engineering Mathematics, University of Bristol, Bristol, UK.
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30
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Jones KDJ, Hesketh T, Yudkin J. Extensively drug-resistant tuberculosis in sub-Saharan Africa: an emerging public-health concern. Trans R Soc Trop Med Hyg 2008; 102:219-24. [PMID: 18243260 DOI: 10.1016/j.trstmh.2007.11.014] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2007] [Revised: 11/27/2007] [Accepted: 11/27/2007] [Indexed: 11/19/2022] Open
Abstract
The extensively drug-resistant tuberculosis (XDR-TB) categorisation has been developed as a phenotypic description of those TB strains that are resistant to most conventional anti-TB drugs. While widely accepted to have significant incidence in those areas, such as Eastern Europe, that have high levels of multidrug resistance, recent reports have described a cluster of XDR-TB cases in the KwaZulu-Natal province of South Africa. With very high case-fatality rates in this setting and a paucity of potential treatment options, concerns have grown about the possibility of an outbreak of highly lethal TB occurring in areas where TB prevalence, generally, is at its highest. In this article, we review previously documented case series of XDR-TB, and examine questions around the likelihood of rapid XDR-TB expansion in sub-Saharan Africa. We analyse how current TB control measures in the area might cope with such a challenge, and identify new areas for focus within the research and development community.
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Affiliation(s)
- Kelsey D J Jones
- UCL Centre for International Health and Development, The Institute of Child Health, London, UK.
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31
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32
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Abstract
Multidrug-resistant tuberculosis (MDR-TB) with bacillary resistance to at least isoniazid and rifampicin in vitro is a worldwide phenomenon. Hot spots of the disease are found scattered in different continents. Prevention of its development through good tuberculosis control programmes operating under the directly observed therapy, short-course (DOTS) strategy is of paramount importance. However, with established MDR-TB, treatment with alternative and specific chemotherapy is necessary to achieve a beneficial outcome. Such an approach on a programme basis is currently known as the 'DOTS-Plus' strategy. Second-line (reserve) drugs utilized in the treatment of MDR-TB are generally less potent and more toxic, perhaps with the notable exceptions of some fluoroquinolones and injectable agents. Surgery has a distinct adjunctive role for the management of MDR-TB in selected patients. The emergence of extensively drug-resistant tuberculosis (XDR-TB), that is, MDR-TB with additional bacillary resistance to the fluoroquinolones and injectables, has provided a very alarming challenge to global health, as the disease currently has a low cure rate and high mortality. In order to combat XDR-TB, strengthening of DOTS and DOTS-Plus programmes is mandatory, especially in the face of surging HIV infection. Furthermore, more attention needs to be focused on developing new drugs with potent bactericidal and sterilizing activities and low side-effects, and above all, drugs that are affordable for communities worldwide.
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Affiliation(s)
- Wing Wai Yew
- Tuberculosis and Chest Unit, Grantham Hospital, Hong Kong, China.
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33
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Warner DF, Mizrahi V. Tuberculosis chemotherapy: the influence of bacillary stress and damage response pathways on drug efficacy. Clin Microbiol Rev 2006; 19:558-70. [PMID: 16847086 PMCID: PMC1539104 DOI: 10.1128/cmr.00060-05] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The global tuberculosis (TB) control effort is focused on interrupting transmission of the causative agent, Mycobacterium tuberculosis, through chemotherapeutic intervention in active infectious disease. The insufficiency of this approach is manifest in the inexorable annual increase in TB infection and mortality rates and the emergence of multidrug-resistant isolates. Critically, the limited efficacy of the current frontline anti-TB drug combination suggests that heterogeneity of host and bacillary physiologies might impair drug activity. This review explores the possibility that strategies enabling adaptation of M. tuberculosis to hostile in vivo conditions might contribute to the subversion of anti-TB chemotherapy. In particular, evidence that infecting bacilli are exposed to environmental and host immune-mediated DNA-damaging insults suggests a role for error-prone DNA repair synthesis in the generation of chromosomally encoded antibiotic resistance mutations. The failure of frontline anti-TB drugs to sterilize a population of susceptible bacilli is independent of genetic resistance, however, and instead implies the operation of alternative tolerance mechanisms. Specifically, it is proposed that the emergence of persister subpopulations might depend on the switch to an altered metabolic state mediated by the stringent response alarmone, (p)ppGpp, possibly involving some or all of the many toxin-antitoxin modules identified in the M. tuberculosis genome.
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Affiliation(s)
- Digby F Warner
- Molecular Mycobacteriology Research Unit, Centre of Excellence for Biomedical TB Research, School of Pathology, University of the Witwatersrand and NHLS, P.O. Box 1038, Johannesburg 2000, South Africa.
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Toro JC, Hoffner S, Linde C, Andersson M, Andersson J, Grundström S. Enhanced susceptibility of multidrug resistant strains of Mycobacterium tuberculosis to granulysin peptides correlates with a reduced fitness phenotype. Microbes Infect 2006; 8:1985-93. [PMID: 16793311 DOI: 10.1016/j.micinf.2006.02.030] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2005] [Revised: 01/31/2006] [Accepted: 02/24/2006] [Indexed: 11/18/2022]
Abstract
Previously it was shown that the antimicrobial protein granulysin possesses potent membranolytic activity against Mycobacterium tuberculosis. Here we demonstrate that granF2 and G13, which are two short synthetic peptides derived from granulysin, inhibited the in vitro growth of clinical isolates of both multidrug resistant and drug susceptible strains of M. tuberculosis. Importantly, a particularly high activity against multidrug resistant M. tuberculosis correlated with a reduced growth rate compared to drug susceptible strains. A synergistic antibacterial effect of granF2 was further observed in combination with ethambutol, a compound with a documented effect on cell wall permeability. This finding suggests that granF2 and ethambutol exert their functions at different levels of the mycobacterial surface. Upon infection of macrophages in vitro, granF2 but not G13 efficiently reduced the intracellular growth of multidrug resistant M. tuberculosis in the presence of the pore-forming protein streptolysin O. The apoptotic function of granF2 apparently promoted destruction of host cells whereby the peptide gained access to and killed intracellular bacteria. Thus, a cost of resistance and a subsequent reduced fitness, measured as decreased growth among multidrug resistant strains of M. tuberculosis, could be associated with increased susceptibility to natural immune defense mechanisms, such as antimicrobial peptides of granulysin. However, a robust cell wall and the membrane of cells still provide physical shelter for the bacteria that may spare sensitive M. tuberculosis stains from being killed.
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Affiliation(s)
- Juan Carlos Toro
- Swedish Institute for Infectious Disease Control, Department of Bacteriology, 171 82 Solna, Sweden
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Russell AD. Biocide use and antibiotic resistance: the relevance of laboratory findings to clinical and environmental situations. THE LANCET. INFECTIOUS DISEASES 2003; 3:794-803. [PMID: 14652205 DOI: 10.1016/s1473-3099(03)00833-8] [Citation(s) in RCA: 238] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Antibiotics are used as chemotherapeutic drugs, and biocides are used as antiseptics, disinfectants, and preservatives. Several factors affect biocidal activity, notably concentration, period of contact, pH, temperature, the presence of interfering material, and the types, numbers, location, and condition of microorganisms. Bacterial cells as part of natural or artificial (laboratory) biofilm communities are much less susceptible than planktonic cells to antibiotics and biocides. Assessment of biocidal activity by bactericidal testing is more relevant than by determination of minimum inhibitory concentrations. Biocides and antibiotics may show some similarities in their mechanisms of action and common mechanisms of bacterial insusceptibility may apply, but there are also major differences. In the laboratory, bacteria can become less susceptible to some biocides. Decreased resistance may be stable or unstable and may be accompanied by a low-level increase in antibiotic resistance. Laboratory studies are useful for examining stress responses and basic mechanisms of action and of bacterial insusceptibility to antibacterial agents. Translation of such findings to the clinical and environmental situations to provide evidence of a possible relation between biocide use and clinical antibiotic resistance is difficult and should be viewed with caution.
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Affiliation(s)
- A D Russell
- Welsh School of Pharmacy, Cardiff University, Cardiff, UK.
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Abstract
Bacterial adaptation to antibiotics has been very successful and over the past decade the increase in antibiotic resistance has generated considerable medical problems. Even though many drug resistances confer a fitness cost, suggesting that they might disappear by reducing the volume of antibiotic use, increasing evidence obtained from laboratory and epidemiological studies indicate that several processes will act to cause long-term persistence of resistant bacteria. Compensatory evolution that ameliorates the costs of resistance, the occurrence of cost-free resistances and genetic linkage between non-selected and selected resistances will confer a stabilization of the resistant bacteria. Thus, it is of importance that we forcefully implement strategies to reduce the rate of appearance and spread of resistant bacteria to allow new drug discovery to catch up with bacterial resistance development.
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Affiliation(s)
- Dan I Andersson
- Swedish Institute for Infectious Disease Control, Dept. of Bacteriology, Nobels väg 18, S-171 82, Stockholm, Sweden.
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Gillespie SH, Billington OJ, Breathnach A, McHugh TD. Multiple drug-resistant Mycobacterium tuberculosis: evidence for changing fitness following passage through human hosts. Microb Drug Resist 2003; 8:273-9. [PMID: 12523624 DOI: 10.1089/10766290260469534] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Recent studies have shown a difference in the genotype of resistant bacteria following passage in animals compared to those passaged in vitro. This suggests that organisms rapidly adapt to their environment of growth. We sought to investigate whether this phenomenon occurred in human infection and whether changes could be detected in the fitness (growth velocity) of isolates transmitted between human hosts. Isogenic strains of Mycobacterium tuberculosis were obtained from a well-documented hospital outbreak. The subjects included those who were HIV seropositive and immunocompromised. The relative fitness of each sample was measured using growth competition in vitro. The results confirmed that our method of measuring fitness was not influenced by the storage conditions of the isolates, and demonstrated that the fitness of genetically similar isolates obtained from different patients in the outbreak differed significantly, as reflected in the growth velocity of the strains. This study provides the first evidence that multiple drug resistant M. tuberculosis strains adapt to the environment of their human host.
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Affiliation(s)
- Stephen H Gillespie
- Department of Medical Microbiology, Royal Free and University College Medical School, London NW3 2PF, UK.
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Cohen T, Sommers B, Murray M. The effect of drug resistance on the fitness of Mycobacterium tuberculosis. THE LANCET. INFECTIOUS DISEASES 2003; 3:13-21. [PMID: 12505028 DOI: 10.1016/s1473-3099(03)00483-3] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Mycobacterium tuberculosis remains a leading infectious cause of morbidity and mortality. While antibiotic resistance is cited as a potential threat to efforts aimed at controlling the spread of this pathogen, it is not clear how drug resistance affects disease dynamics. The effect of mutational events that lead to antibiotic-resistant phenotypes may or may not have a predictable effect on the fitness of drug-resistant tuberculosis strains. Here, we review the literature on laboratory studies of the fitness of drug-resistant tuberculosis, we examine the evidence from cluster studies, and we consider the effect of drug resistance on disease dynamics in mathematical models. On the basis of these diverse lines of evidence, we conclude that the fitness estimates of drug-resistant M tuberculosis are quite heterogeneous and that this variation may preclude our ability to predict future trends of this pathogen.
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Affiliation(s)
- Ted Cohen
- Department of Epidemiology, Harvard School of Public Health, Boston, MA 02115, USA
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Wichelhaus TA, Böddinghaus B, Besier S, Schäfer V, Brade V, Ludwig A. Biological cost of rifampin resistance from the perspective of Staphylococcus aureus. Antimicrob Agents Chemother 2002; 46:3381-5. [PMID: 12384339 PMCID: PMC128759 DOI: 10.1128/aac.46.11.3381-3385.2002] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Resistance determinants that interfere with normal physiological processes in the bacterial cell usually cause a reduction in biological fitness. Fitness assays revealed that 17 of 18 in vitro-selected chromosomal mutations within the rpoB gene accounting for rifampin resistance in Staphylococcus aureus were associated with a reduction in the level of fitness. There was no obvious correlation between the level of resistance to rifampin and the level of fitness loss caused by rpoB mutations. Among 23 clinical rifampin-resistant S. aureus isolates from six countries, only seven different rpoB genotypes could be identified, whereby the mutation 481His-->Asn was present in 21 (91%) of these 23 isolates. The mutation 481His-->Asn, in turn, which confers low-level rifampin resistance on its own, was not shown to be associated with a cost of resistance in vitro. The restriction to distinct mutations that confer rifampin resistance in vivo, as demonstrated here, appears to be determined by the Darwinian fitness of the organisms.
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Affiliation(s)
- Thomas A Wichelhaus
- Institut für Medizinische Mikrobiologie, Klinikum der Johann Wolfgang Goethe-Universität, Frankfurt am Main, Germany.
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Gillespie SH. Evolution of drug resistance in Mycobacterium tuberculosis: clinical and molecular perspective. Antimicrob Agents Chemother 2002; 46:267-74. [PMID: 11796329 PMCID: PMC127054 DOI: 10.1128/aac.46.2.267-274.2002] [Citation(s) in RCA: 288] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Affiliation(s)
- Stephen H Gillespie
- Royal Free and University College Medical School, University College London, London NW3 2PF, United Kingdom.
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Campbell JW, Cronan JE. Bacterial fatty acid biosynthesis: targets for antibacterial drug discovery. Annu Rev Microbiol 2002; 55:305-32. [PMID: 11544358 DOI: 10.1146/annurev.micro.55.1.305] [Citation(s) in RCA: 366] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The increase in drug-resistant pathogenic bacteria has created an urgent demand for new antibiotics. Among the more attractive targets for the development of new antibacterial compounds are the enzymes of fatty acid biosynthesis. Although a number of potent inhibitors of microbial fatty acid biosynthesis have been discovered, few of these are clinically useful drugs. Several of these fatty acid biosynthesis inhibitors have potential as lead compounds in the development of new antibacterials. This review encompasses the known inhibitors and prospective targets for new antibacterials.
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Affiliation(s)
- J W Campbell
- Department of Microbiology University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
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Abstract
Antibiotic resistance poses a serious threat to modern medical practice making treatment more difficult and is associated with increased mortality among patients infected with resistant organisms. There is clear evidence that acquisition of resistance is associated with a decrease in the fitness of the organisms at least in the short term. Evidence from in vitro experiments indicates that bacteria have the ability to adapt to this deficit and recover fitness on serial passage. More recent results show that identical organisms isolated from patients in outbreaks have an initial deficit but that adaptation occurs in vivo. Strategies directed towards controlling resistance must move beyond wishful thinking that supposes that these organisms will disappear merely with control of prescribing. In some cases, resistance will not disappear because there is no evolutionary disadvantage in being resistant once adaptation has taken place. It is important, therefore, that we direct our efforts towards preventing primary resistance emerging and in limiting the spread of resistant strains. Ultimately, we must look again to new drug discovery to improve our therapeutic armoury.
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Affiliation(s)
- S H Gillespie
- Royal Free and University College Medical School, Royal Free Campus, Rowland Hill Street, London NW3 2PF, UK.
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