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Xiong XS, Zhang XD, Yan JW, Huang TT, Liu ZZ, Li ZK, Wang L, Li F. Identification of Mycobacterium tuberculosis Resistance to Common Antibiotics: An Overview of Current Methods and Techniques. Infect Drug Resist 2024; 17:1491-1506. [PMID: 38628245 PMCID: PMC11020249 DOI: 10.2147/idr.s457308] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2024] [Accepted: 03/26/2024] [Indexed: 04/19/2024] Open
Abstract
Multidrug-resistant tuberculosis (MDR-TB) is an essential cause of tuberculosis treatment failure and death of tuberculosis patients. The rapid and reliable profiling of Mycobacterium tuberculosis (MTB) drug resistance in the early stage is a critical research area for public health. Then, most traditional approaches for detecting MTB are time-consuming and costly, leading to the inappropriate therapeutic schedule resting on the ambiguous information of MTB drug resistance, increasing patient economic burden, morbidity, and mortality. Therefore, novel diagnosis methods are frequently required to meet the emerging challenges of MTB drug resistance distinguish. Considering the difficulty in treating MDR-TB, it is urgently required for the development of rapid and accurate methods in the identification of drug resistance profiles of MTB in clinical diagnosis. This review discussed recent advances in MTB drug resistance detection, focusing on developing emerging approaches and their applications in tangled clinical situations. In particular, a brief overview of antibiotic resistance to MTB was present, referred to as intrinsic bacterial resistance, consisting of cell wall barriers and efflux pumping action and acquired resistance caused by genetic mutations. Then, different drug susceptibility test (DST) methods were described, including phenotype DST, genotype DST and novel DST methods. The phenotype DST includes nitrate reductase assay, RocheTM solid ratio method, and liquid culture method and genotype DST includes fluorescent PCR, GeneXpert, PCR reverse dot hybridization, ddPCR, next-generation sequencing and gene chips. Then, novel DST methods were described, including metabolism testing, cell-free DNA probe, CRISPR assay, and spectral analysis technique. The limitations, challenges, and perspectives of different techniques for drug resistance are also discussed. These methods significantly improve the detection sensitivity and accuracy of multidrug-resistant tuberculosis (MRT) and can effectively curb the incidence of drug-resistant tuberculosis and accelerate the process of tuberculosis eradication.
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Affiliation(s)
- Xue-Song Xiong
- Department of Laboratory Medicine, The Affiliated Huai’an Hospital of Yangzhou University, Huai’an, Jiangsu Province, People’s Republic of China
- Department of Laboratory Medicine, The Fifth People’s Hospital of Huai’an, Huai’an, Jiangsu Province, People’s Republic of China
| | - Xue-Di Zhang
- Department of Laboratory Medicine, Xuzhou Infectious Diseases Hospital, Xuzhou, Jiangsu Province, People’s Republic of China
| | - Jia-Wei Yan
- Department of Laboratory Medicine, Xuzhou Infectious Diseases Hospital, Xuzhou, Jiangsu Province, People’s Republic of China
| | - Ting-Ting Huang
- Department of Laboratory Medicine, The Affiliated Huai’an Hospital of Yangzhou University, Huai’an, Jiangsu Province, People’s Republic of China
- Department of Laboratory Medicine, The Fifth People’s Hospital of Huai’an, Huai’an, Jiangsu Province, People’s Republic of China
| | - Zhan-Zhong Liu
- Department of Pharmacy, Xuzhou Infectious Diseases Hospital, Xuzhou, Jiangsu Province, People’s Republic of China
| | - Zheng-Kang Li
- Department of Laboratory Medicine, Guangdong Provincial People’s Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, Guangzhou, Guangdong Province, People’s Republic of China
| | - Liang Wang
- Department of Laboratory Medicine, Guangdong Provincial People’s Hospital (Guangdong Academy of Medical Sciences), Southern Medical University, Guangzhou, Guangdong Province, People’s Republic of China
| | - Fen Li
- Department of Laboratory Medicine, The Affiliated Huai’an Hospital of Yangzhou University, Huai’an, Jiangsu Province, People’s Republic of China
- Department of Laboratory Medicine, The Fifth People’s Hospital of Huai’an, Huai’an, Jiangsu Province, People’s Republic of China
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Wang M, Xie Z, Li L, Chen Y, Li Y, Wang Y, Lu B, Zhang S, Ma F, Ma C, Lin L, Liao Q. Supplementation with compound polysaccharides contributes to the development and metabolic activity of young rat intestinal microbiota. Food Funct 2019; 10:2658-2675. [DOI: 10.1039/c8fo02565g] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Compound polysaccharides may be used as a functional food to modulate the composition and metabolism of gut microbiota, and to help maintain the health of the intestinal microecosystem.
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Affiliation(s)
- Mengxia Wang
- School of Pharmaceutical Sciences
- Guangzhou University of Chinese Medicine
- Guangzhou
- P. R. China
| | - Zhiyong Xie
- School of Pharmaceutical Sciences (Shenzhen)
- Sun Yat-sen University
- Guangzhou
- P. R. China
- Guangdong Provincial Key Laboratory of New Drug Design and Evaluation
| | - Lin Li
- School of Pharmaceutical Sciences
- Guangzhou University of Chinese Medicine
- Guangzhou
- P. R. China
| | - Yongxiong Chen
- School of Pharmaceutical Sciences
- Guangzhou University of Chinese Medicine
- Guangzhou
- P. R. China
| | - Yuan Li
- School of Pharmaceutical Sciences
- Guangzhou University of Chinese Medicine
- Guangzhou
- P. R. China
| | | | - Biyu Lu
- School of Pharmaceutical Sciences
- Guangzhou University of Chinese Medicine
- Guangzhou
- P. R. China
| | - Shaobao Zhang
- School of Pharmaceutical Sciences (Shenzhen)
- Sun Yat-sen University
- Guangzhou
- P. R. China
| | - Fangli Ma
- Infinitus (China) Company Ltd
- Guangzhou
- China
| | | | - Lei Lin
- School of Pharmaceutical Sciences (Shenzhen)
- Sun Yat-sen University
- Guangzhou
- P. R. China
| | - Qiongfeng Liao
- School of Pharmaceutical Sciences
- Guangzhou University of Chinese Medicine
- Guangzhou
- P. R. China
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García-Heredia A, Pohane AA, Melzer ES, Carr CR, Fiolek TJ, Rundell SR, Lim HC, Wagner JC, Morita YS, Swarts BM, Siegrist MS. Peptidoglycan precursor synthesis along the sidewall of pole-growing mycobacteria. eLife 2018; 7:37243. [PMID: 30198841 PMCID: PMC6191288 DOI: 10.7554/elife.37243] [Citation(s) in RCA: 75] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2018] [Accepted: 09/09/2018] [Indexed: 12/25/2022] Open
Abstract
Rod-shaped mycobacteria expand from their poles, yet d-amino acid probes label cell wall peptidoglycan in this genus at both the poles and sidewall. We sought to clarify the metabolic fates of these probes. Monopeptide incorporation was decreased by antibiotics that block peptidoglycan synthesis or l,d-transpeptidation and in an l,d-transpeptidase mutant. Dipeptides complemented defects in d-alanine synthesis or ligation and were present in lipid-linked peptidoglycan precursors. Characterizing probe uptake pathways allowed us to localize peptidoglycan metabolism with precision: monopeptide-marked l,d-transpeptidase remodeling and dipeptide-marked synthesis were coincident with mycomembrane metabolism at the poles, septum and sidewall. Fluorescent pencillin-marked d,d-transpeptidation around the cell perimeter further suggested that the mycobacterial sidewall is a site of cell wall assembly. While polar peptidoglycan synthesis was associated with cell elongation, sidewall synthesis responded to cell wall damage. Peptidoglycan editing along the sidewall may support cell wall robustness in pole-growing mycobacteria.
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Affiliation(s)
- Alam García-Heredia
- Molecular and Cellular Biology Graduate Program, University of Massachusetts, Amherst, United States
| | - Amol Arunrao Pohane
- Department of Microbiology, University of Massachusetts, Amherst, United States
| | - Emily S Melzer
- Department of Microbiology, University of Massachusetts, Amherst, United States
| | - Caleb R Carr
- Department of Microbiology, University of Massachusetts, Amherst, United States
| | - Taylor J Fiolek
- Department of Chemistry and Biochemistry, Central Michigan University, Mount Pleasant, United States
| | - Sarah R Rundell
- Department of Chemistry and Biochemistry, Central Michigan University, Mount Pleasant, United States
| | - Hoong Chuin Lim
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, United States
| | - Jeffrey C Wagner
- Department of Immunology and Infectious Disease, Harvard T.H. Chan School of Public Health, Boston, United States
| | - Yasu S Morita
- Molecular and Cellular Biology Graduate Program, University of Massachusetts, Amherst, United States.,Department of Microbiology, University of Massachusetts, Amherst, United States
| | - Benjamin M Swarts
- Department of Chemistry and Biochemistry, Central Michigan University, Mount Pleasant, United States
| | - M Sloan Siegrist
- Molecular and Cellular Biology Graduate Program, University of Massachusetts, Amherst, United States.,Department of Microbiology, University of Massachusetts, Amherst, United States
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Marshall DD, Halouska S, Zinniel DK, Fenton RJ, Kenealy K, Chahal HK, Rathnaiah G, Barletta RG, Powers R. Assessment of Metabolic Changes in Mycobacterium smegmatis Wild-Type and alr Mutant Strains: Evidence of a New Pathway of d-Alanine Biosynthesis. J Proteome Res 2017; 16:1270-1279. [PMID: 28121156 DOI: 10.1021/acs.jproteome.6b00871] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
In mycobacteria, d-alanine is an essential precursor for peptidoglycan biosynthesis. The only confirmed enzymatic pathway to form d-alanine is through the racemization of l-alanine by alanine racemase (Alr, EC 5.1.1.1). Nevertheless, the essentiality of Alr in Mycobacterium tuberculosis and Mycobacterium smegmatis for cell survivability in the absence of d-alanine has been a point of controversy with contradictory results reported in the literature. To address this issue, we examined the effects of alr inactivation on the cellular metabolism of M. smegmatis. The M. smegmatis alr insertion mutant TAM23 exhibited essentially identical growth to wild-type mc2155 in the absence of d-alanine. NMR metabolomics revealed drastically distinct phenotypes between mc2155 and TAM23. A metabolic switch was observed for TAM23 as a function of supplemented d-alanine. In the absence of d-alanine, the metabolic response directed carbon through an unidentified transaminase to provide the essential d-alanine required for survival. The process is reversed when d-alanine is available, in which the d-alanine is directed to peptidoglycan biosynthesis. Our results provide further support for the hypothesis that Alr is not an essential function of M. smegmatis and that specific Alr inhibitors will have no bactericidal action.
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Affiliation(s)
- Darrell D Marshall
- Department of Chemistry, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0304, United States
| | - Steven Halouska
- Department of Chemistry, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0304, United States
| | - Denise K Zinniel
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68583-0905, United States
| | - Robert J Fenton
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68583-0905, United States
| | - Katie Kenealy
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68583-0905, United States
| | - Harpreet K Chahal
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68583-0905, United States
| | - Govardhan Rathnaiah
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68583-0905, United States
| | - Raúl G Barletta
- School of Veterinary Medicine and Biomedical Sciences, University of Nebraska-Lincoln , Lincoln, Nebraska 68583-0905, United States.,Center for Redox Biology, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0662, United States
| | - Robert Powers
- Department of Chemistry, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0304, United States.,Center for Redox Biology, University of Nebraska-Lincoln , Lincoln, Nebraska 68588-0662, United States
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Whalen KL, Chau AC, Spies MA. In silico optimization of a fragment-based hit yields biologically active, high-efficiency inhibitors for glutamate racemase. ChemMedChem 2013; 8:1681-9. [PMID: 23929705 PMCID: PMC4040332 DOI: 10.1002/cmdc.201300271] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2013] [Indexed: 11/06/2022]
Abstract
A novel lead compound for inhibition of the antibacterial drug target, glutamate racemase (GR), was optimized for both ligand efficiency and lipophilic efficiency. A previously developed hybrid molecular dynamics-docking and scoring scheme, FERM-SMD, was used to predict relative potencies of potential derivatives prior to chemical synthesis. This scheme was successful in distinguishing between high- and low-affinity binders with minimal experimental structural information, saving time and resources in the process. In vitro potency was increased approximately fourfold against GR from the model organism, B. subtilis. Lead derivatives show two- to fourfold increased antimicrobial potency over the parent scaffold. In addition, specificity toward B. subtilis over E. coli and S. aureus depends on the substituent added to the parent scaffold. Finally, insight was gained into the capacity for these compounds to reach the target enzyme in vivo using a bacterial cell wall lysis assay. The outcome of this study is a novel small-molecule inhibitor of GR with the following characteristics: Ki=2.5 μM, LE=0.45 kcal mol(-1) atom(-1), LiPE=6.0, MIC50=260 μg mL(-1) against B. subtilis, EC50, lysis=520 μg mL(-1) against B. subtilis.
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Affiliation(s)
- Katie L. Whalen
- Dr. M. A. Spies Ms. K. L. Whalen Div. of Medicinal and Natural Products Chemistry, Dept. of Biochemistry University of Iowa 115 S. Grand Avenue, Iowa City, IA 52242
- Ms. K. L. Whalen Mr. A. Chau Department of Biochemistry University of Illinois at Urbana-Champaign 600 S. Mathews Avenue, Urbana, IL 61801
| | - Anthony C. Chau
- Ms. K. L. Whalen Mr. A. Chau Department of Biochemistry University of Illinois at Urbana-Champaign 600 S. Mathews Avenue, Urbana, IL 61801
| | - M. Ashley Spies
- Dr. M. A. Spies Ms. K. L. Whalen Div. of Medicinal and Natural Products Chemistry, Dept. of Biochemistry University of Iowa 115 S. Grand Avenue, Iowa City, IA 52242
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Chen JM, Uplekar S, Gordon SV, Cole ST. A point mutation in cycA partially contributes to the D-cycloserine resistance trait of Mycobacterium bovis BCG vaccine strains. PLoS One 2012; 7:e43467. [PMID: 22912881 PMCID: PMC3422274 DOI: 10.1371/journal.pone.0043467] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2012] [Accepted: 07/20/2012] [Indexed: 11/18/2022] Open
Abstract
In mycobacteria, CycA a D-serine, L- and D-alanine, and glycine transporter also functions in the uptake of D-cycloserine, an important second-line anti-tubercular drug. A single nucleotide polymorphism identified in the cycA gene of BCG was hypothesized to contribute to the increased resistance of Mycobacterium bovis bacillus Calmette-Guérin (BCG) to D-cycloserine compared to wild-type Mycobacterium tuberculosis or Mycobacterium bovis. Working along these lines, a merodiploid strain of BCG expressing Mycobacterium tuberculosis CycA was generated and found to exhibit increased susceptibility to D-cycloserine albeit not to the same extent as wild-type Mycobacterium tuberculosis or Mycobacterium bovis. In addition, recombinant Mycobacterium smegmatis strains expressing either Mycobacterium tuberculosis or Mycobacterium bovis CycA but not BCG CycA were rendered more susceptible to D-cycloserine. These findings support the notion that CycA-mediated uptake in BCG is impaired as a result of a single nucleotide polymorphism; however, the partial contribution of this impairment to D-cycloserine resistance suggests the involvement of additional genetic lesions in this phenotype.
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Affiliation(s)
- Jeffrey M Chen
- École Polytechnique Fédérale de Lausanne, Global Health Institute, Lausanne, Switzerland.
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7
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Structure of the Mycobacterium tuberculosis D-alanine:D-alanine ligase, a target of the antituberculosis drug D-cycloserine. Antimicrob Agents Chemother 2010; 55:291-301. [PMID: 20956591 DOI: 10.1128/aac.00558-10] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
D-alanine:D-alanine ligase (EC 6.3.2.4; Ddl) catalyzes the ATP-driven ligation of two D-alanine (D-Ala) molecules to form the D-alanyl:D-alanine dipeptide. This molecule is a key building block in peptidoglycan biosynthesis, making Ddl an attractive target for drug development. D-Cycloserine (DCS), an analog of D-Ala and a prototype Ddl inhibitor, has shown promise for the treatment of tuberculosis. Here, we report the crystal structure of Mycobacterium tuberculosis Ddl at a resolution of 2.1 Å. This structure indicates that Ddl is a dimer and consists of three discrete domains; the ligand binding cavity is at the intersection of all three domains and conjoined by several loop regions. The M. tuberculosis apo Ddl structure shows a novel conformation that has not yet been observed in Ddl enzymes from other species. The nucleotide and D-alanine binding pockets are flexible, requiring significant structural rearrangement of the bordering regions for entry and binding of both ATP and D-Ala molecules. Solution affinity and kinetic studies showed that DCS interacts with Ddl in a manner similar to that observed for D-Ala. Each ligand binds to two binding sites that have significant differences in affinity, with the first binding site exhibiting high affinity. DCS inhibits the enzyme, with a 50% inhibitory concentration (IC(50)) of 0.37 mM under standard assay conditions, implicating a preferential and weak inhibition at the second, lower-affinity binding site. Moreover, DCS binding is tighter at higher ATP concentrations. The crystal structure illustrates potential drugable sites that may result in the development of more-effective Ddl inhibitors.
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Abstract
Modern chemotherapy has played a major role in our control of tuberculosis. Yet tuberculosis still remains a leading infectious disease worldwide, largely owing to persistence of tubercle bacillus and inadequacy of the current chemotherapy. The increasing emergence of drug-resistant tuberculosis along with the HIV pandemic threatens disease control and highlights both the need to understand how our current drugs work and the need to develop new and more effective drugs. This review provides a brief historical account of tuberculosis drugs, examines the problem of current chemotherapy, discusses the targets of current tuberculosis drugs, focuses on some promising new drug candidates, and proposes a range of novel drug targets for intervention. Finally, this review addresses the problem of conventional drug screens based on inhibition of replicating bacilli and the challenge to develop drugs that target nonreplicating persistent bacilli. A new generation of drugs that target persistent bacilli is needed for more effective treatment of tuberculosis.
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Affiliation(s)
- Ying Zhang
- Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, Maryland 21205, USA.
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Mahapatra S, Scherman H, Brennan PJ, Crick DC. N Glycolylation of the nucleotide precursors of peptidoglycan biosynthesis of Mycobacterium spp. is altered by drug treatment. J Bacteriol 2005; 187:2341-7. [PMID: 15774877 PMCID: PMC1065221 DOI: 10.1128/jb.187.7.2341-2347.2005] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The peptidoglycan of Mycobacterium spp. reportedly has some unique features, including the occurrence of N-glycolylmuramic rather than N-acetylmuramic acid. However, very little is known of the actual biosynthesis of mycobacterial peptidoglycan, including the extent and origin of N glycolylation. In the present work, we have isolated and analyzed muramic acid residues located in peptidoglycan and UDP-linked precursors of peptidoglycan from Mycobacterium tuberculosis and Mycobacterium smegmatis. The muramic acid residues isolated from the mature peptidoglycan of both species were shown to be a mixture of the N-acetyl and N-glycolyl derivatives, not solely the N-glycolylated product as generally reported. The isolated UDP-linked N-acylmuramyl-pentapeptide precursor molecules also contain a mixture of N-acetyl and N-glycolyl muramyl residues in apparent contrast to previous observations in which the precursors isolated after treatment with d-cycloserine consisted entirely of N-glycolyl muropeptides. However, nucleotide-linked peptidoglycan precursors isolated from M. tuberculosis treated with d-cycloserine contained only N-glycolylmuramyl-tripeptide precursors, whereas those from similarly treated M. smegmatis consisted of a mixture of N-glycolylated and N-acetylated residues. The full pentapeptide intermediate, isolated following vancomycin treatment of M. smegmatis, consisted of the N-glycolyl derivative only, whereas the corresponding M. tuberculosis intermediate was a mixture of both the N-glycolyl and N-acetyl products. Thus, treatment with vancomycin and d-cylcoserine not only caused an accumulation of nucleotide-linked intermediate compounds but also altered their glycolylation status, possibly by altering the normal equilibrium maintained by de novo biosynthesis and peptidoglycan recycling.
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Affiliation(s)
- Sebabrata Mahapatra
- Mycobacteria Research Laboratories, Department of Microbiology, Immunology and Pathology, Colorado State University, Fort Collins, CO 80523, USA
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Feng Z, Barletta RG. Roles of Mycobacterium smegmatis D-alanine:D-alanine ligase and D-alanine racemase in the mechanisms of action of and resistance to the peptidoglycan inhibitor D-cycloserine. Antimicrob Agents Chemother 2003; 47:283-91. [PMID: 12499203 PMCID: PMC149019 DOI: 10.1128/aac.47.1.283-291.2003] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
D-Cycloserine (DCS) targets the peptidoglycan biosynthetic enzymes D-alanine racemase (Alr) and D-alanine:D-alanine ligase (Ddl). Previously, we demonstrated that the overproduction of Alr in Mycobacterium smegmatis determines a DCS resistance phenotype. In this study, we investigated the roles of both Alr and Ddl in the mechanisms of action of and resistance to DCS in M. smegmatis. We found that the overexpression of either the M. smegmatis or the Mycobacterium tuberculosis ddl gene in M. smegmatis confers resistance to DCS, but at lower levels than the overexpression of the alr gene. Furthermore, a strain overexpressing both the alr and ddl genes displayed an eightfold-higher level of resistance. To test the hypothesis that inhibition of Alr by DCS decreases the intracellular pool of D-alanine, we determined the alanine pools in M. smegmatis wild-type and recombinant strains with or without DCS treatment. Alr-overproducing strain GPM14 cells not exposed to DCS displayed almost equimolar amounts of L- and D-alanine in the steady state. The wild-type strain and Ddl-overproducing strains contained a twofold excess of L- over D-alanine. In all strains, DCS treatment led to a significant accumulation of L-alanine and a concomitant decease of D-alanine, with approximately a 20-fold excess of L-alanine in the Ddl-overproducing strains. These data suggest that Ddl is not significantly inhibited by DCS at concentrations that inhibit Alr. This study is of significance for the identification of the lethal target(s) of DCS and the development of novel drugs targeting the D-alanine branch of mycobacterial peptidoglycan biosynthesis.
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Affiliation(s)
- Zhengyu Feng
- Department of Veterinary and Biomedical Sciences, University of Nebraska, Lincoln, Nebraska 68583-0905, USA
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Chacon O, Feng Z, Harris NB, Cáceres NE, Adams LG, Barletta RG. Mycobacterium smegmatis D-Alanine Racemase Mutants Are Not Dependent on D-Alanine for Growth. Antimicrob Agents Chemother 2002; 46:47-54. [PMID: 11751110 PMCID: PMC126997 DOI: 10.1128/aac.46.2.47-54.2002] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Mycobacterium smegmatis is a fast-growing nonpathogenic species particularly useful in studying basic cellular processes of relevance to pathogenic mycobacteria. This study focused on the D-alanine racemase gene (alrA), which is involved in the synthesis of D-alanine, a basic component of peptidoglycan that forms the backbone of the cell wall. M. smegmatis alrA null mutants were generated by homologous recombination using a kanamycin resistance marker for insertional inactivation. Mutants were selected on Middlebrook medium supplemented with 50 mM D-alanine and 20 microg of kanamycin per ml. These mutants were also able to grow in standard and minimal media without D-alanine, giving rise to colonies with a drier appearance and more-raised borders than the wild-type strain. The viability of the mutants and independence of D-alanine for growth indicate that inactivation of alrA does not impose an auxotrophic requirement for D-alanine, suggesting the existence of a new pathway of D-alanine biosynthesis in M. smegmatis. Biochemical analysis demonstrated the absence of any detectable D-alanine racemase activity in the mutant strains. In addition, the alrA mutants displayed hypersusceptibility to the antimycobacterial agent D-cycloserine. The MIC of D-cycloserine for the mutant strain was 2.56 microg/ml, 30-fold less than that for the wild-type strain. Furthermore, this hypersusceptibility was confirmed by the bactericidal action of D-cycloserine on broth cultures. The kinetic of killing for the mutant strain followed the same pattern as that for the wild-type strain, but at a 30-fold-lower drug concentration. This effect does not involve a change in the permeability of the cell wall by this drug and is consistent with the identification of D-alanine racemase as a target of D-cycloserine. This outcome is of importance for the design of novel antituberculosis drugs targeting peptidoglycan biosynthesis in mycobacteria.
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Affiliation(s)
- Ofelia Chacon
- Department of Veterinary and Biomedical Sciences, University of Nebraska, Lincoln, Nebraska 68583-0905, USA
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