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Lovering AL, Gretes MC, Safadi SS, Danel F, de Castro L, Page MGP, Strynadka NCJ. Structural insights into the anti-methicillin-resistant Staphylococcus aureus (MRSA) activity of ceftobiprole. J Biol Chem 2012; 287:32096-102. [PMID: 22815485 DOI: 10.1074/jbc.m112.355644] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is an antibiotic-resistant strain of S. aureus afflicting hospitals and communities worldwide. Of greatest concern is its development of resistance to current last-line-of-defense antibiotics; new therapeutics are urgently needed to combat this pathogen. Ceftobiprole is a recently developed, latest generation cephalosporin and has been the first to show activity against MRSA by inhibiting essential peptidoglycan transpeptidases, including the β-lactam resistance determinant PBP2a, from MRSA. Here we present the structure of the complex of ceftobiprole bound to PBP2a. This structure provides the first look at the molecular details of an effective β-lactam-resistant PBP interaction, leading to new insights into the mechanism of ceftobiprole efficacy against MRSA.
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Affiliation(s)
- Andrew L Lovering
- Department of Biochemistry and Molecular Biology and the Center for Blood Research, University of British Columbia, Vancouver, British Columbia, Canada
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102
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Qamar A, Golemi-Kotra D. Dual roles of FmtA in Staphylococcus aureus cell wall biosynthesis and autolysis. Antimicrob Agents Chemother 2012; 56:3797-805. [PMID: 22564846 PMCID: PMC3393393 DOI: 10.1128/aac.00187-12] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2012] [Accepted: 04/29/2012] [Indexed: 11/20/2022] Open
Abstract
The fmtA gene is a member of the Staphylococcus aureus core cell wall stimulon. The FmtA protein interacts with β-lactams through formation of covalent species. Here, we show that FmtA has weak D-Ala-D-Ala-carboxypeptidase activity and is capable of covalently incorporating C14-Gly into cell walls. The fluorescence microscopy study showed that the protein is localized to the cell division septum. Furthermore, we show that wall teichoic acids interact specifically with FmtA and mediate recruitment of FmtA to the S. aureus cell wall. Subjection of S. aureus to FmtA concentrations of 0.1 μM or less induces autolysis and biofilm production. This effect requires the presence of wall teichoic acids. At FmtA concentrations greater than 0.2 μM, autolysis and biofilm formation in S. aureus are repressed and growth is enhanced. Our findings indicate dual roles of FmtA in S. aureus growth, whereby at low concentrations, FmtA may modulate the activity of the major autolysin (AtlA) of S. aureus and, at high concentrations, may participate in synthesis of cell wall peptidoglycan. These two roles of FmtA may reflect dual functions of FmtA in the absence and presence of cell wall stress, respectively.
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103
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Broadening the spectrum of β-lactam antibiotics through inhibition of signal peptidase type I. Antimicrob Agents Chemother 2012; 56:4662-70. [PMID: 22710113 DOI: 10.1128/aac.00726-12] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The resistance of methicillin-resistant Staphylococcus aureus (MRSA) to all β-lactam classes limits treatment options for serious infections involving this organism. Our goal is to discover new agents that restore the activity of β-lactams against MRSA, an approach that has led to the discovery of two classes of natural product antibiotics, a cyclic depsipeptide (krisynomycin) and a lipoglycopeptide (actinocarbasin), which potentiate the activity of imipenem against MRSA strain COL. We report here that these imipenem synergists are inhibitors of the bacterial type I signal peptidase SpsB, a serine protease that is required for the secretion of proteins that are exported through the Sec and Tat systems. A synthetic derivative of actinocarbasin, M131, synergized with imipenem both in vitro and in vivo with potent efficacy. The in vitro activity of M131 extends to clinical isolates of MRSA but not to a methicillin-sensitive strain. Synergy is restricted to β-lactam antibiotics and is not observed with other antibiotic classes. We propose that the SpsB inhibitors synergize with β-lactams by preventing the signal peptidase-mediated secretion of proteins required for β-lactam resistance. Combinations of SpsB inhibitors and β-lactams may expand the utility of these widely prescribed antibiotics to treat MRSA infections, analogous to β-lactamase inhibitors which restored the utility of this antibiotic class for the treatment of resistant Gram-negative infections.
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104
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Lama A, Pané-Farré J, Chon T, Wiersma AM, Sit CS, Vederas JC, Hecker M, Nakano MM. Response of methicillin-resistant Staphylococcus aureus to amicoumacin A. PLoS One 2012; 7:e34037. [PMID: 22479511 PMCID: PMC3316591 DOI: 10.1371/journal.pone.0034037] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2011] [Accepted: 02/21/2012] [Indexed: 11/18/2022] Open
Abstract
Amicoumacin A exhibits strong antimicrobial activity against methicillin-resistant Staphylococcus aureus (MRSA), hence we sought to uncover its mechanism of action. Genome-wide transcriptome analysis of S. aureus COL in response to amicoumacin A showed alteration in transcription of genes specifying several cellular processes including cell envelope turnover, cross-membrane transport, virulence, metabolism, and general stress response. The most highly induced gene was lrgA, encoding an antiholin-like product, which is induced in cells undergoing a collapse of Δψ. Consistent with the notion that LrgA modulates murein hydrolase activity, COL grown in the presence of amicoumacin A showed reduced autolysis, which was primarily caused by lower hydrolase activity. To gain further insight into the mechanism of action of amicoumacin A, a whole genome comparison of wild-type COL and amicoumacin A-resistant mutants isolated by a serial passage method was carried out. Single point mutations generating codon substitutions were uncovered in ksgA (encoding RNA dimethyltransferase), fusA (elongation factor G), dnaG (primase), lacD (tagatose 1,6-bisphosphate aldolase), and SACOL0611 (a putative glycosyl transferase). The codon substitutions in EF-G that cause amicoumacin A resistance and fusidic acid resistance reside in separate domains and do not bring about cross resistance. Taken together, these results suggest that amicoumacin A might cause perturbation of the cell membrane and lead to energy dissipation. Decreased rates of cellular metabolism including protein synthesis and DNA replication in resistant strains might allow cells to compensate for membrane dysfunction and thus increase cell survivability.
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Affiliation(s)
- Amrita Lama
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Beaverton, Oregon, United States of America
| | - Jan Pané-Farré
- Institute for Microbiology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany
| | - Tai Chon
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Beaverton, Oregon, United States of America
| | - Anna M. Wiersma
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Clarissa S. Sit
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - John C. Vederas
- Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada
| | - Michael Hecker
- Institute for Microbiology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany
| | - Michiko M. Nakano
- Division of Environmental and Biomolecular Systems, Institute of Environmental Health, Oregon Health & Science University, Beaverton, Oregon, United States of America
- * E-mail:
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105
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Dzhekieva L, Kumar I, Pratt RF. Inhibition of Bacterial DD-Peptidases (Penicillin-Binding Proteins) in Membranes and in Vivo by Peptidoglycan-Mimetic Boronic Acids. Biochemistry 2012; 51:2804-11. [DOI: 10.1021/bi300148v] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Liudmila Dzhekieva
- Department of Chemistry, Wesleyan University, Lawn Avenue, Middletown, Connecticut 06459,
United
States
| | - Ish Kumar
- School of Natural
Sciences, Fairleigh Dickinson University, Teaneck, New Jersey 07666, United States
| | - R. F. Pratt
- Department of Chemistry, Wesleyan University, Lawn Avenue, Middletown, Connecticut 06459,
United
States
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106
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Hwang J, Tseitin V, Ramnarayan K, Shenderovich MD, Inouye M. Structure-based design and screening of inhibitors for an essential bacterial GTPase, Der. J Antibiot (Tokyo) 2012; 65:237-43. [PMID: 22377538 DOI: 10.1038/ja.2012.9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Der is an essential and widely conserved GTPase that assists assembly of a large ribosomal subunit in bacteria. Der associates specifically with the 50S subunit in a GTP-dependent manner and the cells depleted of Der accumulate the structurally unstable 50S subunit, which dissociates into an aberrant subunit at a lower Mg(2+) concentration. As Der is an essential and ubiquitous protein in bacteria, it may prove to be an ideal cellular target against which new antibiotics can be developed. In the present study, we describe our attempts to identify novel antibiotics specifically targeting Der GTPase. We performed the structure-based design of Der inhibitors using the X-ray crystal structure of Thermotoga maritima Der (TmDer). Virtual screening of commercially available chemical library retrieved 257 small molecules that potentially inhibit Der GTPase activity. These 257 chemicals were tested for their in vitro effects on TmDer GTPase and in vivo antibacterial activities. We identified three structurally diverse compounds, SBI-34462, -34566 and -34612, that are both biologically active against bacterial cells and putative enzymatic inhibitors of Der GTPase homologs. We also presented the possible interactions of each compound with the Der GTP-binding site to understand the mechanism of inhibition. Therefore, our lead compounds inhibiting Der GTPase provide scaffolds for the development of novel antibiotics against antibiotic-resistant pathogenic bacteria.
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Affiliation(s)
- Jihwan Hwang
- Department of Biochemistry, Center for Advanced Biotechnology and Medicine, University of Medicine and Dentistry of New Jersey, Piscataway, NJ 08854, USA
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107
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My NH, Hirao H, Van DU, Morokuma K. Computational Studies of Bacterial Resistance to β-Lactam Antibiotics: Mechanism of Covalent Inhibition of the Penicillin-Binding Protein 2a (PBP2a). J Chem Inf Model 2011; 51:3226-34. [DOI: 10.1021/ci2004175] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Nguyen Hoa My
- Faculty of Chemistry, Hanoi University of Natural Science, VNU, 19 Le Thanh Tong, Hanoi, Vietnam
| | - Hajime Hirao
- Fukui Institute for Fundamental Chemistry, Kyoto University, 34-4 Takano Nishihiraki-cho, Sakyo, Kyoto 606-8103, Japan
- Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371
| | - Dang Ung Van
- Faculty of Chemistry, Hanoi University of Natural Science, VNU, 19 Le Thanh Tong, Hanoi, Vietnam
- Hoa Binh University, CC2, My Dinh II, Tu Liem, Hanoi, Vietnam
| | - Keiji Morokuma
- Fukui Institute for Fundamental Chemistry, Kyoto University, 34-4 Takano Nishihiraki-cho, Sakyo, Kyoto 606-8103, Japan
- Cherry L. Emerson Center for Scientific Computation and Department of Chemistry, Emory University, Atlanta, Georgia 30322, United States
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108
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Nemmara VV, Dzhekieva L, Sarkar KS, Adediran SA, Duez C, Nicholas RA, Pratt RF. Substrate specificity of low-molecular mass bacterial DD-peptidases. Biochemistry 2011; 50:10091-101. [PMID: 22029692 DOI: 10.1021/bi201326a] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The bacterial DD-peptidases or penicillin-binding proteins (PBPs) catalyze the formation and regulation of cross-links in peptidoglycan biosynthesis. They are classified into two groups, the high-molecular mass (HMM) and low-molecular mass (LMM) enzymes. The latter group, which is subdivided into classes A-C (LMMA, -B, and -C, respectively), is believed to catalyze DD-carboxypeptidase and endopeptidase reactions in vivo. To date, the specificity of their reactions with particular elements of peptidoglycan structure has not, in general, been defined. This paper describes the steady-state kinetics of hydrolysis of a series of specific peptidoglycan-mimetic peptides, representing various elements of stem peptide structure, catalyzed by a range of LMM PBPs (the LMMA enzymes, Escherichia coli PBP5, Neisseria gonorrhoeae PBP4, and Streptococcus pneumoniae PBP3, and the LMMC enzymes, the Actinomadura R39 dd-peptidase, Bacillus subtilis PBP4a, and N. gonorrhoeae PBP3). The R39 enzyme (LMMC), like the previously studied Streptomyces R61 DD-peptidase (LMMB), specifically and rapidly hydrolyzes stem peptide fragments with a free N-terminus. In accord with this result, the crystal structures of the R61 and R39 enzymes display a binding site specific to the stem peptide N-terminus. These are water-soluble enzymes, however, with no known specific function in vivo. On the other hand, soluble versions of the remaining enzymes of those noted above, all of which are likely to be membrane-bound and/or associated in vivo and have been assigned particular roles in cell wall biosynthesis and maintenance, show little or no specificity for peptides containing elements of peptidoglycan structure. Peptidoglycan-mimetic boronate transition-state analogues do inhibit these enzymes but display notable specificity only for the LMMC enzymes, where, unlike peptide substrates, they may be able to effectively induce a specific active site structure. The manner in which LMMA (and HMM) DD-peptidases achieve substrate specificity, both in vitro and in vivo, remains unknown.
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Affiliation(s)
- Venkatesh V Nemmara
- Department of Chemistry, Wesleyan University, Lawn Avenue, Middletown, Connecticut 06459, USA
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109
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Wang Z, Jing ZW, Zhou CX, Zhang L, Cheng J, Zhang ZJ, Liu J, Xu CS, Li PT, Wang YY. Fusion of core pathways reveals a horizontal synergistic mechanism underlying combination therapy. Eur J Pharmacol 2011; 667:278-86. [DOI: 10.1016/j.ejphar.2011.05.046] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2010] [Revised: 05/01/2011] [Accepted: 05/17/2011] [Indexed: 01/04/2023]
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110
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Galletti P, Cocuzza CEA, Pori M, Quintavalla A, Musumeci R, Giacomini D. Antibacterial Agents and Cystic Fibrosis: Synthesis and Antimicrobial Evaluation of a Series of N-Thiomethylazetidinones. ChemMedChem 2011; 6:1919-27. [DOI: 10.1002/cmdc.201100282] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 07/07/2011] [Indexed: 01/29/2023]
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111
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Kotsakis SD, Tzouvelekis LS, Zerva L, Liakopoulos A, Petinaki E. Staphylococcus lugdunensis strain with a modified PBP1A/1B expressing resistance to β-lactams. Eur J Clin Microbiol Infect Dis 2011; 31:169-72. [PMID: 21594555 DOI: 10.1007/s10096-011-1289-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2011] [Accepted: 04/26/2011] [Indexed: 11/24/2022]
Abstract
We describe for the first time the emergence of an mecA-negative Staphylococcus lugdunensis strain with a modified PBP1A/1B that expresses resistance to all β-lactams. A duplication of the tetrapeptide S(569)AYG, which is part of the transpeptidase domain of PBP1A/1B and closely located to the K(583)TG catalytic motif, was associated with this unusual phenotype.
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Affiliation(s)
- S D Kotsakis
- Department of Microbiology, University Hospital of Larissa, Larissa, Greece
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112
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Kaushik D, Rathi S, Jain A. Ceftaroline: a comprehensive update. Int J Antimicrob Agents 2011; 37:389-95. [PMID: 21420284 DOI: 10.1016/j.ijantimicag.2011.01.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2010] [Revised: 12/14/2010] [Accepted: 01/19/2011] [Indexed: 10/18/2022]
Abstract
Ceftaroline is a novel broad-spectrum cephalosporin antibiotic currently under US Food and Drug Administration (FDA) review for a new drug application (NDA), filed by Cerexa, Inc. (a wholly owned subsidiary of Forest Laboratories), for the treatment of complicated skin and skin-structure infections (cSSSIs) and community-associated pneumonia (CAP). The antibiotic acts by binding to penicillin-binding proteins in bacteria, consistent with other β-lactams. The antimicrobial spectrum of ceftaroline ranges from aerobic and anaerobic Gram-positive bacteria, including drug-resistant isolates of staphylococci, i.e. heterogeneous vancomycin-intermediate Staphylococcus aureus (hVISA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA), to anaerobic Gram-negative pathogens such as Moraxella catarrhalis and Haemophilus influenzae (including β-lactamase-positive strains), as well as bacteria with multiple resistance phenotypes. Ceftaroline fosamil is the prodrug that is rapidly dephosphorylated by in vivo plasma phosphatases to the active drug ceftaroline, which follows a two-compartmental pharmacokinetic model and is eliminated primarily by renal excretion, with a plasma half-life of ca. 2.5 h. Ceftaroline is well tolerated, which is consistent with its good safety profile similar to other cephalosporins in clinical trials. Thus, it would be a promising drug to fight multidrug-resistant superbugs such as S. aureus and Streptococcus pneumoniae for the treatment of cSSSIs and CAP.
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Affiliation(s)
- Darpan Kaushik
- Department of Pharmaceutical Chemistry, Rajendra Institute of Technology & Sciences, 4th Mile Stone, Hisar Road, Sirsa 125055, Haryana, India.
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113
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Microtiter plate-based assay for inhibitors of penicillin-binding protein 2a from methicillin-resistant Staphylococcus aureus. Antimicrob Agents Chemother 2011; 55:2783-7. [PMID: 21402836 DOI: 10.1128/aac.01327-10] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Penicillin-binding protein 2a (PBP2a), the molecular determinant for high-level β-lactam resistance in methicillin-resistant Staphylococcus aureus (MRSA), is intrinsically resistant to most β-lactam antibiotics. The development and characterization of new inhibitors targeting PBP2a would benefit from an effective and convenient assay for inhibitor binding. This study was directed toward the development of a fluorescently detected β-lactam binding assay for PBP2a from MRSA. Biotinylated ampicillin and biotinylated cephalexin were tested as tagging reagents for fluorescence detection by using a streptavidin-horseradish peroxidase conjugate. Both bound surprisingly well to PBP2a, with binding constants of 1.6 ± 0.4 μM and 13.6 ± 0.8 μM, respectively. Two forms of the assay were developed, a one-step direct competition form of the assay and a two-step indirect competition form of the assay, and both forms of the assay gave comparable results. This assay was then used to characterize PBP2a binding to ceftobiprole, which gave results consistent with previous studies of ceftobiprole-PBP2a binding. This assay was also demonstrated for screening for PBP2a inhibitors by screening a set of 13 randomly selected β-lactams for PBP2a inhibition at 750 μM. Meropenem was observed to give substantial inhibition in this screen, and a follow-up titration experiment determined its apparent K(i) to be 480 ± 70 μM. The availability of convenient and sensitive microtiter-plate based assays for the screening and characterization of PBP2a inhibitors is expected to facilitate the discovery and development of new PBP2a inhibitors for use in combating the serious public health problem posed by MRSA.
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114
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Wang Z, Liu J, Cheng Y, Wang Y. Fangjiomics: in search of effective and safe combination therapies. J Clin Pharmacol 2011; 51:1132-51. [PMID: 21209238 DOI: 10.1177/0091270010382913] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Millennia-old Chinese medicine treats disease with many combination therapies involving ingredients used in clinic practice. Fangjiomics is the science of identifying and designing effective mixtures of bioactive agents and elucidating their modes of action beyond those of Chinese patent medicines. Omics profiling and quantitative optimal modeling have been used to associate the various responses with biological pathways related to disease phenotype. Fangjiomics seeks to study myriad compatible combinations that may act through multiple targets, modes of action, and biological pathways balancing on off-target and on-target effects. This approach may lead to the discovery of controllable array-designed therapies to combine less potent elements that are more effective collectively but have fewer adverse side effects than does any element singly.
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Affiliation(s)
- Zhong Wang
- Institute of Basic Research in Clinical Medicine, China Academy of Chinese Medical Sciences, Beijing, China.
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115
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Hardej D, Ashby CR, Khadtare NS, Kulkarni SS, Singh S, Talele TT. The synthesis of phenylalanine-derived C5-substituted rhodanines and their activity against selected methicillin-resistant Staphylococcus aureus (MRSA) strains. Eur J Med Chem 2010; 45:5827-32. [DOI: 10.1016/j.ejmech.2010.09.045] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2010] [Revised: 09/14/2010] [Accepted: 09/20/2010] [Indexed: 11/25/2022]
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116
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Biek D, Critchley IA, Riccobene TA, Thye DA. Ceftaroline fosamil: a novel broad-spectrum cephalosporin with expanded anti-Gram-positive activity. J Antimicrob Chemother 2010; 65 Suppl 4:iv9-16. [PMID: 21115457 DOI: 10.1093/jac/dkq251] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023] Open
Abstract
Ceftaroline fosamil is a novel cephalosporin with broad-spectrum activity against Gram-positive pathogens, including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant Streptococcus pneumoniae, and common Gram-negative organisms. The activity of ceftaroline against MRSA is attributed to its ability to bind to penicillin-binding protein (PBP) 2a with high affinity and inhibit the biochemical activity of PBP 2a more efficiently than other presently available β-lactams. The activity of ceftaroline against MRSA and the β-haemolytic streptococci makes it an attractive monotherapy agent for the treatment of complicated skin and skin structure infections (cSSSIs). Recent profiling and surveillance studies have shown that ceftaroline is active against contemporary skin pathogens collected from US and European medical centres in 2008. The mean free drug %T > MIC (percentage of time the drug concentration remains above the MIC) needed for stasis ranged from 26% for S. aureus to 39% for S. pneumoniae in the murine thigh infection model. Pharmacokinetic and pharmacodynamic target attainment predictions for 600 mg of ceftaroline fosamil every 12 h showed that the mean %T > MICs for which plasma free-drug concentrations exceeded an MIC of 1 and 2 mg/L were 71% and 51% of the dosing interval, respectively. For a 40% T > MIC target, the predicted attainments for infections due to pathogens for which ceftaroline MICs were 1 or 2 mg/L were 100% and 90%, respectively. Clinical and microbiological successes of ceftaroline fosamil in treating cSSSIs were demonstrated in two Phase III clinical studies, in which 96.8% of all baseline cSSSI isolates from the microbiologically evaluable population were inhibited by ceftaroline at ≤ 2 mg/L. Ceftaroline fosamil is a promising broad-spectrum agent for the treatment of cSSSIs.
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117
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β-Lactam and glycopeptide antibiotics: first and last line of defense? Trends Biotechnol 2010; 28:596-604. [PMID: 20970210 DOI: 10.1016/j.tibtech.2010.09.004] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2010] [Revised: 09/06/2010] [Accepted: 09/20/2010] [Indexed: 01/21/2023]
Abstract
Most infections are caused by bacteria, many of which are ever-evolving and resistant to nearly all available antibiotics. β-Lactams and glycopeptides are used to combat these infections by inhibiting bacterial cell-wall synthesis. This mechanism remains an interesting target in the search for new antibiotics in light of failed genomic approaches and the limited input of major pharmaceutical companies. Several strategies have enriched the pipeline of bacterial cell-wall inhibitors; examples include combining screening strategies with lesser-explored microbial diversity, or reinventing known scaffolds based on structure-function relationships. Drugs developed using novel strategies will contribute to the arsenal in fight against the continued emergence of bacterial resistance.
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118
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Rossolini GM, Mantengoli E, Montagnani F, Pollini S. Epidemiology and clinical relevance of microbial resistance determinants versus anti-Gram-positive agents. Curr Opin Microbiol 2010; 13:582-8. [DOI: 10.1016/j.mib.2010.08.006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2010] [Revised: 08/19/2010] [Accepted: 08/23/2010] [Indexed: 10/19/2022]
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119
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Pohlmann J, Vasilevich NI, Glushkov AI, Kellenberger L, Shapiro S, Caspers P, Page MGP, Danel F. Propenylamide and propenylsulfonamide cephalosporins as a novel class of anti-MRSA beta-lactams. Bioorg Med Chem Lett 2010; 20:4635-8. [PMID: 20576430 DOI: 10.1016/j.bmcl.2010.05.110] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Revised: 05/27/2010] [Accepted: 05/29/2010] [Indexed: 11/15/2022]
Abstract
Novel C(3) propenylamide and propenylsulfonamide cephalosporins have been synthesized and tested for their ability to inhibit the penicillin-binding protein 2' (PBP2') from Staphylococcus epidermidis and the growth of a panel of clinically relevant bacterial species, including methicillin-resistant Staphylococcus aureus (MRSA). The most potent compounds inhibited the growth of MRSA strains with minimum inhibitory concentrations (MIC) as low as 1 microg/mL. The structure-activity relationship revealed the potential for further optimization of this new cephalosporin class.
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Affiliation(s)
- Jens Pohlmann
- Basilea Pharmaceutica International Ltd, CH-4005 Basel, Switzerland.
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120
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Bernal P, Lemaire S, Pinho MG, Mobashery S, Hinds J, Taylor PW. Insertion of epicatechin gallate into the cytoplasmic membrane of methicillin-resistant Staphylococcus aureus disrupts penicillin-binding protein (PBP) 2a-mediated beta-lactam resistance by delocalizing PBP2. J Biol Chem 2010; 285:24055-65. [PMID: 20516078 PMCID: PMC2911331 DOI: 10.1074/jbc.m110.114793] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Epicatechin gallate (ECg) sensitizes methicillin-resistant Staphylococcus aureus (MRSA) to oxacillin and other beta-lactam agents; it also reduces the secretion of virulence-associated proteins, prevents biofilm formation, and induces gross morphological changes in MRSA cells without compromising the growth rate. MRSA is resistant to oxacillin because of the presence of penicillin-binding protein 2a (PBP2a), which allows peptidoglycan synthesis to continue after oxacillin-mediated acylation of native PBPs. We show that ECg binds predominantly to the cytoplasmic membrane (CM), initially decreasing the fluidity of the bilayer, and induces changes in gene expression indicative of an attempt to preserve and repair a compromised cell wall. On further incubation, the CM is reorganized; the amount of lysylphosphatidylglycerol is markedly reduced, with a concomitant increase in phosphatidylglycerol, and the proportion of branched chain fatty acids increases, resulting in a more fluid structure. We found no evidence that ECg modulates the enzymatic activity of PBP2a through direct binding to the protein but determined that PBP2 is delocalized from the FtsZ-anchored cell wall biosynthetic machinery at the septal division site following intercalation into the CM. We argue that many features of the ECg-induced phenotype can be explained by changes in the fluid dynamics of the CM.
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Affiliation(s)
- Patricia Bernal
- School of Pharmacy, University of London, London WC1N 1AX, United Kingdom
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121
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Abstract
AbstractStaphylococcus aureus is the third most dreaded pathogen posing a severe threat due to its refractory behavior against the current armamentarium of antimicrobial drugs. This is attributed to the evolution of an array of resistance mechanisms responsible for morbidity and mortality globally. Local and international travel has resulted in the movement of drug resistant S. aureus clones from hospitals into communities and further into different geographical areas where they have been responsible for epidemic outbreaks. Thus, there is a dire necessity to refrain further cross movement of these multidrug resistant clones across the globe. The plausible alternative to prevent this situation is by thorough implementation of regulatory aspects of sanitation, formulary usage and development of new therapeutic interventions. Various strategies like exploring novel antibacterial targets, high throughput screening of microbes, combinatorial and synthetic chemistry, combinatorial biosynthesis and vaccine development are being extensively sought to overcome multidrug resistant chronic Staphylococcal infections. The majority of the antibacterial drugs are of microbial origin and are prone to being resisted. Anti-staphylococcal plant natural products that may provide a new alternative to overcome the refractory S.aureus under clinical settings have grossly been unnoticed. The present communication highlights the new chemical entities and therapeutic modalities that are entering the pharmaceutical market or are in the late stages of clinical evaluation to overcome multidrug resistant Staphylococcal infections. The review also explores the possibility of immunity and enzyme-based interventions as new therapeutic modalities and highlights the regulatory concerns on the prescription, usage and formulary development in the developed and developing world to keep the new chemical entities and therapeutic modalities viable to overcome antimicrobial resistance in S. aureus.
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122
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Staub I, Sieber SA. Beta-lactam probes as selective chemical-proteomic tools for the identification and functional characterization of resistance associated enzymes in MRSA. J Am Chem Soc 2009; 131:6271-6. [PMID: 19354235 DOI: 10.1021/ja901304n] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
With the development of antibiotic resistant bacterial strains, infectious diseases have become again a life threatening problem. One of the reasons for this dilemma is the limited number and breadth of current therapeutic targets for which several resistance strategies have evolved over time. To identify resistance associated targets and to understand their function, activity, and regulation, we utilized a novel strategy based on small synthetic beta-lactam molecules that were applied in activity based protein profiling experiments (ABPP) to comparatively profile in situ enzyme activities in antibiotic sensitive and resistant S. aureus strains (MRSA). Several enzyme activities which are unique to the MRSA strain including known resistant associated targets, involved in cell wall biosynthesis and antibiotic sensing, could be identified. In addition, we also identified uncharacterized enzymes which turned out to be capable of hydrolyzing beta-lactam antibiotics. This technology could therefore represent a valuable tool to monitor the activity and function of other yet unexplored resistance associated enzymes in pathogenic bacteria and help to discover new drug targets for customized therapeutic interventions.
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Affiliation(s)
- Isabell Staub
- Center for Integrated Protein Science Munich CIPSM, Department of Chemistry and Biochemistry, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, 81377 Munich, Germany
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123
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Molecular basis and phenotype of methicillin resistance in Staphylococcus aureus and insights into new beta-lactams that meet the challenge. Antimicrob Agents Chemother 2009; 53:4051-63. [PMID: 19470504 DOI: 10.1128/aac.00084-09] [Citation(s) in RCA: 93] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
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124
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Novel anion liposome-encapsulated antisense oligonucleotide restores susceptibility of methicillin-resistant Staphylococcus aureus and rescues mice from lethal sepsis by targeting mecA. Antimicrob Agents Chemother 2009; 53:2871-8. [PMID: 19433567 DOI: 10.1128/aac.01542-08] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Beta-lactam resistance in methicillin (meticillin)-resistant Staphylococcus aureus (MRSA) is caused by the production of an additional low-affinity penicillin-binding protein 2a, which is encoded by the mecA gene. The disruption of mecA may inhibit mecA expression and thereafter lead to the restoration of MRSA susceptibility to beta-lactams. In this study, we developed a novel anionic liposome for encapsulating and delivering the complexes of a specific anti-mecA phosphorothioate oligodeoxynucleotide (PS-ODN833) and polycation polyethylenimine (PEI). The efficiencies of liposome encapsulation of the complexes were around 79.7% +/- 2.7%. The liposomes showed sustained release of PS-ODN833 at 37 degrees C but very low levels of release at 4 degrees C and room temperature. The addition of the encapsulated anti-mecA PS-ODN833-PEI complex to cultures of MRSA strains caused 45, 76, 82, and 93% reductions in mecA expression, accompanied by the inhibition of MRSA growth on Mueller-Hinton agar containing oxacillin (6 microg/ml) in a concentration-dependent manner. The encapsulated-PS-ODN833 treatment also reduced the MICs of five of the most commonly used antibiotics for MRSA clinical isolates to values within the sensitivity range and rescued mice from MRSA-caused septic death by downregulating mecA. The survival rates of septic mice increased from 0% for the control group to 53% for the PS-ODN833-treated group. The results were associated with reductions of bacterial titers in the blood of surviving mice. The findings of the present study indicate that an antisense oligodeoxynucleotide targeted to mecA can significantly restore the susceptibility of MRSA to existing beta-lactam antibiotics, providing an apparently novel strategy for treating MRSA infections.
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125
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Abstract
Understanding the molecular mechanisms underlying synergistic, potentiative and antagonistic effects of drug combinations could facilitate the discovery of novel efficacious combinations and multi-targeted agents. In this article, we describe an extensive investigation of the published literature on drug combinations for which the combination effect has been evaluated by rigorous analysis methods and for which relevant molecular interaction profiles of the drugs involved are available. Analysis of the 117 drug combinations identified reveals general and specific modes of action, and highlights the potential value of molecular interaction profiles in the discovery of novel multicomponent therapies.
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126
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Perez LRR, Dias C, d'Azevedo PA. Agar dilution and agar screen with cefoxitin and oxacillin: what is known and what is unknown in detection of meticillin-resistant Staphylococcus aureus. J Med Microbiol 2008; 57:954-956. [PMID: 18628494 DOI: 10.1099/jmm.0.46992-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In this study we evaluated the performance of the oxacillin agar screen test, and agar dilution tests using cefoxitin and oxacillin antimicrobials, to detect meticillin resistance in Staphylococcus aureus isolates. The presence of the mecA gene, detected by PCR, was used as the standard to which agar screen and agar dilution tests were compared. The best performance was obtained using the agar dilution test (99.4 % accuracy) with breakpoints of 4 mug ml(-1) for oxacillin and 8 mug ml(-1) for cefoxitin, and using the oxacillin agar screen test. Also, a strong correlation between MIC values of cefoxitin and oxacillin permits the use of either drug for detection of meticillin resistance.
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Affiliation(s)
- Leandro Reus Rodrigues Perez
- Laboratory of Microbiology, Hospital Mãe de Deus, Porto Alegre, RS, Brazil.,Post-Graduate Program in Medical Sciences, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, RS, Brazil
| | - Cícero Dias
- Microbiology Department, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, Porto Alegre, RS, Brazil.,Laboratory of Microbiology, Hospital Mãe de Deus, Porto Alegre, RS, Brazil
| | - Pedro Alves d'Azevedo
- Microbiology Department, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, Porto Alegre, RS, Brazil.,Post-Graduate Program in Medical Sciences, Fundação Faculdade Federal de Ciências Médicas de Porto Alegre, RS, Brazil
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127
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Villegas-Estrada A, Lee M, Hesek D, Vakulenko SB, Mobashery S. Co-opting the cell wall in fighting methicillin-resistant Staphylococcus aureus: potent inhibition of PBP 2a by two anti-MRSA beta-lactam antibiotics. J Am Chem Soc 2008; 130:9212-3. [PMID: 18582062 PMCID: PMC2747592 DOI: 10.1021/ja8029448] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is a global bacterial scourge that has become resistant to many classes of antibiotics, and treatment options for MRSA infections are limited. The cause of MRSA resistance to all commercially available beta-lactam antibiotics is the acquisition of the gene mecA, which encodes penicillin-binding protein 2a (PBP 2a). PBP 2a is a transpeptidase, which in contrast to the other transpeptidases of S. aureus does not experience inhibition by beta-lactam antibiotics. The lack of inhibition is due to a closed conformation for the active site for PBP 2a, which opens up only in the course of the catalytic function of the protein. Here we show that two new anti-MRSA antibiotics now undergoing clinical trials, ceftaroline and ME1036, are able to inhibit PBP 2a effectively, a process that is enhanced in the presence of a cell wall structural surrogate. It is likely that in the course of bacterial growth the occupancy of the allosteric site for the cell wall is co-opted by these antibiotics, and under these conditions the second-order rate constant for the encounter of the antibiotic and PBP 2a approaches the clinically useful value of 10(4)-10(5) M-1 s-1. These compounds are potent inhibitors of PBP 2a as well as PBPs from other species, and have potential as therapeutic agents for treatment of serious infections by MRSA and other resistant bacterial pathogens.
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Affiliation(s)
- Adriel Villegas-Estrada
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
| | - Mijoon Lee
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
| | - Dusan Hesek
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
| | - Sergei B. Vakulenko
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
| | - Shahriar Mobashery
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556
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128
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Murphy JT, Walshe R, Devocelle M. A computational model of antibiotic-resistance mechanisms in methicillin-resistant Staphylococcus aureus (MRSA). J Theor Biol 2008; 254:284-93. [PMID: 18577389 DOI: 10.1016/j.jtbi.2008.05.037] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2007] [Revised: 05/30/2008] [Accepted: 05/30/2008] [Indexed: 11/29/2022]
Abstract
An agent-based model of bacteria-antibiotic interactions has been developed that incorporates the antibiotic-resistance mechanisms of Methicillin-Resistant Staphylococcus aureus (MRSA). The model, called the Micro-Gen Bacterial Simulator, uses information about the cell biology of bacteria to produce global information about population growth in different environmental conditions. It facilitates a detailed systems-level investigation of the dynamics involved in bacteria-antibiotic interactions and a means to relate this information to traditional high-level properties such as the Minimum Inhibitory Concentration (MIC) of an antibiotic. The two main resistance strategies against beta-lactam antibiotics employed by MRSA were incorporated into the model: beta-lactamase enzymes, which hydrolytically cleave antibiotic molecules, and penicillin-binding proteins (PBP2a) with reduced binding affinities for antibiotics. Initial tests with three common antibiotics (penicillin, ampicillin and cephalothin) indicate that the model can be used to generate quantitatively accurate predictions of MICs for antibiotics against different strains of MRSA from basic cellular and biochemical information. Furthermore, by varying key parameters in the model, the relative impact of different kinetic parameters associated with the two resistance mechanisms to beta-lactam antibiotics on cell survival in the presence of antibiotics was investigated.
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Affiliation(s)
- James T Murphy
- Modelling and Scientific Computing Group, School of Computing, Faculty of Engineering and Computing, Dublin City University, Glasnevin, Dublin 9, Ireland.
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129
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Comparative study of the susceptibilities of major epidemic clones of methicillin-resistant Staphylococcus aureus to oxacillin and to the new broad-spectrum cephalosporin ceftobiprole. Antimicrob Agents Chemother 2008; 52:2709-17. [PMID: 18505853 DOI: 10.1128/aac.00266-08] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Multidrug-resistant strains of Staphylococcus aureus continue to increase in frequency worldwide, both in hospitals and in the community, raising serious problems for the chemotherapy of staphylococcal disease. Ceftobiprole (BPR; BAL9141), the active constituent of the prodrug ceftobiprole medocaril (BAL5788), is a new cephalosporin which was already shown to have powerful activity against a number of bacterial pathogens, including S. aureus. In an effort to test possible limits to the antibacterial spectrum and efficacy of BPR, we examined the susceptibilities of the relatively few pandemic methicillin-resistant S. aureus (MRSA) clones that are responsible for the great majority of cases of staphylococcal disease worldwide. We also included in the tests the highly oxacillin-resistant subpopulations that are present with low frequencies in the cultures of these clones. Such subpopulations may represent a natural reservoir from which MRSA strains with decreased susceptibility to BPR may emerge in the future. We also tested the efficacy of BPR against MRSA strains with reduced susceptibility to vancomycin and against MRSA strains carrying the enterococcal vancomycin resistance gene complex. BPR was shown to be uniformly effective against all these resistant MRSA strains, and the mechanism of superb antimicrobial activity correlated with the strikingly increased affinity of the cephalosporin against penicillin-binding protein 2A, the protein product of the antibiotic resistance determinant mecA.
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130
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Lemaire S, Fuda C, Van Bambeke F, Tulkens PM, Mobashery S. Restoration of susceptibility of methicillin-resistant Staphylococcus aureus to beta-lactam antibiotics by acidic pH: role of penicillin-binding protein PBP 2a. J Biol Chem 2008; 283:12769-76. [PMID: 18337244 DOI: 10.1074/jbc.m800079200] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) is a global scourge, and treatment options are becoming limited. The MRSA phenotype reverts to that of beta-lactam-sensitive S. aureus when bacteria are grown at pH 5.0 in broth and, more importantly from a medical perspective (protracted, relapsing infections), after phagocytosis by macrophages, where the bacteria thrive in the acidic environment of phagolysosomes. The central factor for the MRSA phenotype is the function of the penicillin-binding protein (PBP) 2a, which maintains transpeptidase activity while being poorly inhibited by beta-lactams because of a closed conformation of its active site. We document herein by binding, acylation/deacylation kinetics, and circular dichroism spectroscopy with purified PBP 2a that at acidic pH (i) beta-lactams interact with PBP 2a more avidly; (ii) the non-covalent pre-acylation complex exhibits a lower dissociation constant and an increased rate of acyl-enzyme formation (first-order rate constant) without change in hydrolytic deacylation rate; and (iii) PBP 2a undergoes a conformational change in the presence of the antibiotic consistent with the opening of the active site from the closed conformation. These observations argue that PBP 2a most likely evolved for its physiological function at pH 7 or higher by adopting a closed conformation, which is not maintained at acidic pH. Although at the organism level the effect of acidic pH on other biological processes in MRSA could not be discounted, our report should provide the impetus for closer examination of the properties of PBP 2a at low pH and thereby identifying novel points of intervention in combating this problematic organism.
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Affiliation(s)
- Sandrine Lemaire
- Unité de Pharmacologie Cellulaire et Moléculaire, Université Catholique de Louvain, B-1200 Brussels, Belgium.
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131
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Abstract
The purpose of this review is to assess the relative strengths and weaknesses of individual members of the carbapenem class of antibiotics. Clinical trials and review articles were identified from a Medline search (1979 - July 2006), in addition to, reference citations from identified publications, abstracts from the Interscience Conferences on Antimicrobial Agents and Chemotherapy and the 12th International Congress on Infectious Disease, and package inserts. Articles in English were reviewed, with emphasis on those containing efficacy or safety data. Carbapenems bind to critical penicillin-binding proteins, disrupting the growth and structural integrity of bacterial cell walls. They provide enhanced anaerobic and Gram-negative coverage as compared with other beta-lactams and their stability against extended-spectrum beta-lactamases (ESBLs) makes them an effective treatment option. The most common adverse effects are infusion-site complications and gastrointestinal distress. Ertapenem has limited efficacy against non-fermenting, Gram-negative bacteria, restricting its use to community-acquired infections. Imipenem is slightly more effective against Gram-positive organisms and meropenem slightly more effective against Gram-negative organisms. However, both have broad-spectrum activity, including non-fermenting, Gram-negative bacteria. Among non-fermenting, Gram-negatives, resistance to imipenem in particular is increasing. Doripenem is in late-stage clinical development and combines the broad-spectrum coverage of imipenem and meropenem, and more potent activity against Pseudomonas aeruginosa. Due to the increasing challenges represented by ESBLs and multi-drug resistant organisms, the carbapenems are assuming a greater role in the treatment of serious infections. Imipenem and meropenem are presently available and have been shown to be effective against nosocomial infections. Doripenem is an investigational carbapenem that has completed Phase III clinical trials and that has the potential to improve on this efficacy and minimize the emergence of resistance to the carbapenem class.
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Affiliation(s)
- David P Nicolau
- Hartford Hospital, Center for Anti-Infective Research and Development, 80 Seymour Street, Hartford, Connecticut 06102-5037, USA.
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132
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Zapun A, Contreras-Martel C, Vernet T. Penicillin-binding proteins and beta-lactam resistance. FEMS Microbiol Rev 2008; 32:361-85. [PMID: 18248419 DOI: 10.1111/j.1574-6976.2007.00095.x] [Citation(s) in RCA: 386] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
A number of ways and means have evolved to provide resistance to eubacteria challenged by beta-lactams. This review is focused on pathogens that resist by expressing low-affinity targets for these antibiotics, the penicillin-binding proteins (PBPs). Even within this narrow focus, a great variety of strategies have been uncovered such as the acquisition of an additional low-affinity PBP, the overexpression of an endogenous low-affinity PBP, the alteration of endogenous PBPs by point mutations or homologous recombination or a combination of the above.
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Affiliation(s)
- André Zapun
- Laboratoire d'Ingénierie des Macromolécules, Institut de Biologie Structurale Jean-Pierre Ebel, UMR 5075-CNRS, CEA, Université Joseph Fourier, Grenoble, France
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133
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Fan X, Liu Y, Smith D, Konermann L, Siu KWM, Golemi-Kotra D. Diversity of penicillin-binding proteins. Resistance factor FmtA of Staphylococcus aureus. J Biol Chem 2007; 282:35143-52. [PMID: 17925392 DOI: 10.1074/jbc.m706296200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Antibiotic-resistant Staphylococcus aureus is a major concern to public health. Methicillin-resistant S. aureus strains are completely resistant to all beta-lactams antibiotics. One of the main factors involved in methicillin resistance in S. aureus is the penicillin-binding protein, PBP2a. This protein is insensitive to inactivation by beta-lactam antibiotics such as methicillin. Although other proteins are implicated in high and homogeneous levels of methicillin resistance, the functions of these other proteins remain elusive. Herein, we report for the first time on the putative function of one of these proteins, FmtA. This protein specifically interacts with beta-lactam antibiotics forming covalently bound complexes. The serine residue present in the sequence motif Ser-X-X-Lys (which is conserved among penicillin-binding proteins and beta-lactamases) is the active-site nucleophile during the formation of acyl-enzyme species. FmtA has a low binding affinity for beta-lactams, and it experiences a slow acylation rate, suggesting that this protein is intrinsically resistant to beta-lactam inactivation. We found that FmtA undergoes conformational changes in presence of beta-lactams that may be essential to the beta-lactam resistance mechanism. FmtA binds to peptidoglycan in vitro. Our findings suggest that FmtA is a penicillin-binding protein, and as such, it may compensate for suppressed peptidoglycan biosynthesis under beta-lactam induced cell wall stress conditions.
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Affiliation(s)
- Xin Fan
- Department of Chemistry, York University, Toronto, Ontario M3J 1P3, Canada
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134
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Green IR, Tocoli FE, Lee SH, Nihei KI, Kubo I. Molecular design of anti-MRSA agents based on the anacardic acid scaffold. Bioorg Med Chem 2007; 15:6236-41. [PMID: 17601740 DOI: 10.1016/j.bmc.2007.06.022] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Revised: 05/31/2007] [Accepted: 06/12/2007] [Indexed: 10/23/2022]
Abstract
A series of anacardic acid analogues possessing different side chains viz. phenolic, branched, and alicyclic were synthesized and their antibacterial activity tested against methicillin-resistant Staphylococcus aureus (MRSA). The maximum activity against this bacterium occurred with the branched side-chain analogue, 6-(4',8'-dimethylnonyl)salicylic acid, and the alicyclic side-chain analogue, 6-cyclododecylmethyl salicylic acid, with the minimum inhibitory concentration (MIC) of 0.39 microg/mL, respectively. This activity was superior to that of the most potent antibacterial anacardic acid isolated from the cashew Anacardium occidentale (Anacardiaceae), apple and nut, that is, the 6-[8'(Z),11'(Z),14'-pentadecatrienyl]salicylic acid.
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Affiliation(s)
- Ivan R Green
- Department of Chemistry, University of the Western Cape, Bellville 7530, South Africa.
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135
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Cha J, Vakulenko SB, Mobashery S. Characterization of the β-Lactam Antibiotic Sensor Domain of the MecR1 Signal Sensor/Transducer Protein from Methicillin-Resistant Staphylococcus aureus. Biochemistry 2007; 46:7822-31. [PMID: 17550272 DOI: 10.1021/bi7005459] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) has evolved two mechanisms for resistance to beta-lactam antibiotics. One is production of a beta-lactamase, and the other is that of penicillin-binding protein 2a (PBP 2a). The expression of these two proteins is regulated by the bla and mec operons, respectively. BlaR1 and MecR1 are beta-lactam sensor/signal transducer proteins, which experience acylation by beta-lactam antibiotics on the cell surface and transduce the signal into the cytoplasm. The C-terminal surface domain of MecR1 (MecRS) has been cloned, expressed, and purified to homogeneity. This protein has been characterized by documenting that it has a critical and unusual Nzeta-carboxylated lysine at position 394. Furthermore, the kinetics of interactions with beta-lactam antibiotics were evaluated, a process that entails conformational changes for the protein that might be critical for the signal transduction event. Kinetics of acylation of MecRS are suggestive that signal sensing may be the step where the two systems are substantially different from one another.
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Affiliation(s)
- Jooyoung Cha
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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136
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Abstract
Biogenic polyamines (e.g., spermidine and spermine) are a group of essential polycationic compounds found in all living cells. The effects of spermine and spermidine on antibiotic susceptibility were examined with gram-negative Escherichia coli and Salmonella enterica serovar Typhimurium bacteria and clinical isolates of Pseudomonas aeruginosa and with gram-positive Staphylococcus aureus bacteria, including methicillin-resistant S. aureus (MRSA). Exogenous spermine exerted a dose-dependent inhibition effect on the growth of E. coli, S. enterica serovar Typhimurium, and S. aureus but not P. aeruginosa, as depicted by MIC and growth curve measurements. While the MICs of polymyxin and ciprofloxacin were in general increased by exogenous spermine and spermidine in P. aeruginosa, this adverse effect was not observed in enteric bacteria and S. aureus. It was found that spermine and spermidine can decrease the MICs of beta-lactam antibiotics in all strains as well as other types of antibiotics in a strain-dependent manner. Significantly, the MICs of oxacillin for MRSA Mu50 and N315 were decreased more than 200-fold in the presence of spermine, and this effect of spermine was retained when assessed in the presence of divalent ions (magnesium or calcium; 3 mM) or sodium chloride (150 mM). The effect of spermine on the sensitization of P. aeruginosa and MRSA to antibiotics was further demonstrated by population analysis and time-killing assays. The results of checkerboard assays with E. coli and S. aureus indicated a strong synergistic effect of spermine in combination with beta-lactams and chloramphenicol. The decreased MICs of beta-lactams implied that the possible blockage of outer membrane porins by exogenous spermine or spermidine did not play a crucial role in most cases. In contrast, only the MIC of imipenem against P. aeruginosa was increased by exogenous spermine and spermidine, and this resistance effect was abolished in a mutant strain devoid of the outer membrane porin OprD. In E. coli, the MICs of carbenicillin, chloramphenicol, and tetracycline were decreased in two acrA mutants devoid of a major efflux pump, AcrAB. However, retention of the spermine effect on antibiotic susceptibility in two acrA mutants of E. coli suggested that the AcrAB efflux pump was not the target for a synergistic effect by spermine and antibiotics and ruled out the hypothesis of spermine serving as an efflux pump inhibitor in this organism. In summary, this interesting finding of the effect of spermine on antibiotic susceptibility provides the basis for a new potential approach against drug-resistant pathogens by use of existing beta-lactam antibiotics.
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Affiliation(s)
- Dong-Hyeon Kwon
- Department of Biology, Georgia State University, 24 Peachtree Center Avenue, Atlanta, GA 30303, USA
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137
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Lemaire S, Van Bambeke F, Mingeot-Leclercq MP, Glupczynski Y, Tulkens PM. Role of acidic pH in the susceptibility of intraphagocytic methicillin-resistant Staphylococcus aureus strains to meropenem and cloxacillin. Antimicrob Agents Chemother 2007; 51:1627-32. [PMID: 17307986 PMCID: PMC1855560 DOI: 10.1128/aac.01192-06] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Early studies showed that methicillin-resistant Staphylococcus aureus (MRSA) strains are susceptible to beta-lactams when they are exposed to pH < or = 5.5 in broth. Because S. aureus survives in the phagolysosomes of macrophages, where the pH may be acidic, we have examined the susceptibility of MRSA ATCC 33591 phagocytized by human THP-1 macrophages to meropenem (MEM) and cloxacillin (CLX). Using a pharmacodynamic model assessing key pharmacological (50% effective concentration and maximal efficacy) and microbiological (static concentration) descriptors of antibiotic activity, we show that intraphagocytic MRSA strains are as sensitive to MEM and CLX as methicillin-susceptible S. aureus (MSSA; ATCC 25923). This observation was replicated in broth if the pH was brought to 5.5 and was confirmed with clinical strains. Electron microscopy showed that both the MRSA and the MSSA strains localized and multiplied in membrane-bounded structures (phagolysosomes) in the absence of beta-lactams. Incubation of the infected macrophages with ammonium chloride (to raise the phagolysosomal pH) made MRSA insensitive to MEM and CLX. No difference was seen in mec, mecA, mecI, mecR1, femA, and femB expression (reversed transcription-PCR) or in PBP 2a content (immunodetection) in MRSA grown in broth at pH 5.5 compared with that in MRSA grown in broth at 7.4. The level of [(14)C]benzylpenicillin binding to cell walls prepared from a non-beta-lactamase-producing MRSA clinical isolate was two times lower than that to cell walls prepared from MSSA ATCC 25923 at pH 7.4, but the levels increased to similar values for both strains at pH 5.5. These data suggest that the restoration of susceptibility of intraphagocytic of MRSA to MEM and CLX is due to the acidic pH prevailing in phagolysosomes and is mediated by an enhanced binding to penicillin-binding proteins.
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Affiliation(s)
- Sandrine Lemaire
- Unité de Pharmacologie Cellulaire et Moléculaire, Université Catholique de Louvain, UCL 73.70 Avenue E. Mounier 73, B-1200 Brussels, Belgium
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138
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Abstract
Antibacterial discovery research has been driven, medically, commercially and intellectually, by the need for new therapeutics that are not subject to the resistance mechanisms that have evolved to combat previous generations of antibacterial agents. This need has often been equated with the identification and exploitation of novel targets. But efforts towards discovery and development of inhibitors of novel targets have proved frustrating. It might be that the 'good old targets' are qualitatively different from the crop of all possible novel targets. What has been learned from existing targets that can be applied to the quest for new antibacterials?
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Affiliation(s)
- Lynn L Silver
- LL Silver Consulting, Springfield, New Jersey 07081, USA.
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139
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140
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Crisóstomo MI, Vollmer W, Kharat AS, Inhülsen S, Gehre F, Buckenmaier S, Tomasz A. Attenuation of penicillin resistance in a peptidoglycan O-acetyl transferase mutant of Streptococcus pneumoniae. Mol Microbiol 2006; 61:1497-509. [PMID: 16968223 DOI: 10.1111/j.1365-2958.2006.05340.x] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The level of penicillin resistance in clinical isolates of Streptococcus pneumoniae depends not only on the reduced affinity of penicillin binding proteins (PBPs) but also on the functioning of enzymes that modify the stem peptide structure of cell wall precursors. We used mariner mutagenesis in search of additional genetic determinants that may further attenuate the level of penicillin resistance in the bacteria. A mariner mutant of the highly penicillin-resistant S. pneumoniae strain Pen6 showed reduction of the penicillin minimum inhibitory concentration (MIC) from 6 to 0.75 microg ml(-1). Decrease in penicillin MIC was also observed upon introduction of the mutation (named provisionally adr, for attenuator of drug resistance) into representatives of major epidemic clones of penicillin-resistant pneumococci. Attenuation of resistance levels was specific for beta-lactams. The adr mutant has retained unchanged (low affinity) PBPs, unaltered murM gene and unchanged cell wall stem peptide composition, but the mutant became hypersensitive to exogenous lysozyme and complementation experiments showed that both phenotypes--reduced resistance and lysozyme sensitivity--were linked to the defective adr gene. DNA sequence comparison and chemical analysis of the cell wall identified adr as the structural gene of the pneumococcal peptidoglycan O-acetylase.
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Affiliation(s)
- M Inês Crisóstomo
- Laboratory of Microbiology, The Rockefeller University, New York, NY, USA
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141
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Fuda C, Hesek D, Lee M, Heilmayer W, Novak R, Vakulenko SB, Mobashery S. Mechanistic Basis for the Action of New Cephalosporin Antibiotics Effective against Methicillin- and Vancomycin-resistant Staphylococcus aureus. J Biol Chem 2006; 281:10035-41. [PMID: 16459335 DOI: 10.1074/jbc.m508846200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Emergence of methicillin-resistant Staphylococcus aureus (MRSA) has created challenges in treatment of nosocomial infections. The recent clinical emergence of vancomycin-resistant MRSA is a new disconcerting chapter in the evolution of these strains. S. aureus normally produces four PBPs, which are susceptible to modification by beta-lactam antibiotics, an event that leads to bacterial death. The gene product of mecA from MRSA is a penicillin-binding protein (PBP) designated PBP 2a. PBP 2a is refractory to the action of all commercially available beta-lactam antibiotics. Furthermore, PBP 2a is capable of taking over the functions of the other PBPs of S. aureus in the face of the challenge by beta-lactam antibiotics. Three cephalosporins (compounds 1-3) have been studied herein, which show antibacterial activities against MRSA, including the clinically important vancomycin-resistant strains. These cephalosporins exhibit substantially smaller dissociation constants for the preacylation complex compared with the case of typical cephalosporins, but their pseudo-second-order rate constants for encounter with PBP 2a (k(2)/K(s)) are not very large (< or =200 m(-1) s(-1)). It is documented herein that these cephalosporins facilitate a conformational change in PBP 2a, a process that is enhanced in the presence of a synthetic surrogate for cell wall, resulting in increases in the k(2)/K(s) parameter and in more facile enzyme inhibition. These findings argue that the novel cephalosporins are able to co-opt interactions between PBP 2a and the cell wall in gaining access to the active site in the inhibition process, a set of events that leads to effective inhibition of PBP 2a and the attendant killing of the MRSA strains.
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Affiliation(s)
- Cosimo Fuda
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, IN 46556, USA
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142
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Arciola CR, Campoccia D, Gamberini S, Donati ME, Pirini V, Visai L, Speziale P, Montanaro L. Antibiotic resistance in exopolysaccharide-forming Staphylococcus epidermidis clinical isolates from orthopaedic implant infections. Biomaterials 2005; 26:6530-5. [PMID: 15949842 DOI: 10.1016/j.biomaterials.2005.04.031] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2005] [Accepted: 04/12/2005] [Indexed: 11/17/2022]
Abstract
The opportunistic pathogen Staphylococcus epidermidis is able to produce biofilm and to frequently cause implant infections. In recent years, it has also exhibited an increasing antimicrobial drug resistance. Here, the resistance to a panel of 16 different antibiotics in 342 clinical strains of S. epidermidis from orthopaedic implant infections has been investigated. The isolates were pheno- and genotyped for extracellular polysaccharide production, relevant to staphylococcal biofilm formation, in order to ascertain possible associations with antibiotic resistance. Approximately 10% of the isolates were found to be sensitive to all screened antibiotics. In all, 37-38% were resistant to beta-lactams such as oxacillin and imipenem, while the resistance to penicillin, ampicillin, cefazolin, cefamandole, was consistently observed in over 80% of the strains. Erythromycin- and clindamycin- resistant strains were approximately 41% and 16%, respectively. Of the isolates, 10% was resistant to chloramphenicol, 23% to sulfamethoxazole and 26% to ciprofloxacin. Resistance to vancomycin was never observed. Interestingly, exopolysaccharide-producing strains exhibited a significantly higher prevalence in the resistance to the four aminoglycosides (gentamicin, amikacin, netilmicin, tobramycin), to sulfamethoxazole and to ciprofloxacin with respect to non-producing isolates. Moreover, multiple resistance to antibiotics was more frequent among exopolysaccharide-forming strains.
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Affiliation(s)
- Carla Renata Arciola
- Research Unit on Implant Infections, Rizzoli Orthopaedic Institute, Via di Barbiano 1/10, 40136 Bologna, Italy.
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143
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Frère JM, Marchot P. Inactivators in competition. How to deal with them ... and not! Biochem Pharmacol 2005; 70:1417-23. [PMID: 16139804 DOI: 10.1016/j.bcp.2005.07.008] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2005] [Revised: 07/05/2005] [Accepted: 07/08/2005] [Indexed: 11/24/2022]
Abstract
A method is described to determine the values of the equilibrium (K) and rate (k(2)) constants for enzyme inactivations which occur according to two-step pathways involving a first non-covalent complex and a covalent, irreversibly inactivated adduct. The method rests on a competition between a reference compound [R] for which the k(2) and K values are already known and another inactivator [C]. During the experiments, the disappearance of the reference compound or the appearance of the ER(*) adduct is monitored. The analysis shows that under conditions where the k(2) and K values for the competing substrate can be determined, the measured apparent first-order rate constant for the disappearance of the reference compound is not the sum of the rate constants obtained for each inactivator in the absence of the other. The method can be used to determine the K and k(2) constants when an adequate reference compound is available, in particular, for the interactions between beta-lactam antibiotics and penicillin-binding proteins. The precautions which must be taken to avoid large errors on the estimation of the parameters of the competing inactivator are discussed. Examples found in the literature are discussed where an erroneous simplified equation has been utilised, thus yielding incorrect values for k(2) and K. Interestingly, the correct values can be calculated on the basis of the published results which do not contain the raw experimental data. But some of the values should be considered with a lot of caution since the experiments have not been performed under optimal conditions.
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Affiliation(s)
- Jean-Marie Frère
- CIP, Université de Liège, Institut de Chimie B6, Sart-Tilman, B-4000 Liège, Belgium.
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144
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Fisher JF, Meroueh SO, Mobashery S. Bacterial resistance to beta-lactam antibiotics: compelling opportunism, compelling opportunity. Chem Rev 2005; 105:395-424. [PMID: 15700950 DOI: 10.1021/cr030102i] [Citation(s) in RCA: 676] [Impact Index Per Article: 35.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Jed F Fisher
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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145
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Deresinski S. Methicillin-Resistant Staphylococcus aureus: An Evolutionary, Epidemiologic, and Therapeutic Odyssey. Clin Infect Dis 2005; 40:562-73. [PMID: 15712079 DOI: 10.1086/427701] [Citation(s) in RCA: 272] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2004] [Accepted: 11/10/2004] [Indexed: 11/03/2022] Open
Abstract
Methicillin-resistant Staphylococcus aureus, first identified just over 4 decades ago, has undergone rapid evolutionary changes and epidemiologic expansion. It has spread beyond the confines of health care facilities, emerging anew in the community, where it is rapidly becoming a dominant pathogen. This has led to an important change in the choice of antibiotics in the management of community-acquired infections and has also led to the development of novel antimicrobials.
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Affiliation(s)
- Stan Deresinski
- Division of Infectious Disease and Geographic Medicine, Department of Medicine, Stanford University, Stanford, CA, USA.
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146
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Fuda C, Hesek D, Lee M, Morio KI, Nowak T, Mobashery S. Activation for Catalysis of Penicillin-Binding Protein 2a from Methicillin-Resistant Staphylococcus aureus by Bacterial Cell Wall. J Am Chem Soc 2005; 127:2056-7. [PMID: 15713078 DOI: 10.1021/ja0434376] [Citation(s) in RCA: 73] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Methicillin-resistant Staphylococcus aureus (MRSA) has acquired a unique penicillin-binding protein (PBP), PBP 2a, which has rendered the organism resistant to the action of all available beta-lactam antibiotics. The X-ray structure of PBP 2a shows the active site in a closed conformation, consistent with resistance to inhibition by beta-lactam antibiotics. However, it is known that PBP 2a avidly cross-links the S. aureus cell wall, which is its physiological function. It is shown herein that synthetic fragments of the bacterial cell wall bind in a saturable manner to PBP 2a and cause a conformational change in the protein that makes the active site more accessible to binding to a beta-lactam antibiotic. These observations and measurements point to a novel strategy by nature to keep the active site of PBP 2a sheltered from the inhibitory activity of the antibiotics, yet it becomes available to the polymeric cell wall by a requisite conformational change for the critical cell wall cross-linking reaction.
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Affiliation(s)
- Cosimo Fuda
- Department of Chemistry and Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, USA
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147
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Birck C, Cha JY, Cross J, Schulze-Briese C, Meroueh SO, Schlegel HB, Mobashery S, Samama JP. X-ray Crystal Structure of the Acylated β-Lactam Sensor Domain of BlaR1 from Staphylococcus aureus and the Mechanism of Receptor Activation for Signal Transduction. J Am Chem Soc 2004; 126:13945-7. [PMID: 15506754 DOI: 10.1021/ja044742u] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Methicillin-resistant strains of Staphylococcus aureus (MRSA) are the major cause of infections worldwide. Transcription of the beta-lactamase and PBP2a resistance genes is mediated by two closely related signal-transducing integral membrane proteins, BlaR1 and MecR1, upon binding of the beta-lactam inducer to the sensor domain. Herein we report the crystal structure at 1.75 A resolution of the sensor domain of BlaR1 in complex with a cephalosporin antibiotic. Activation of the signal transducer involves acylation of serine 389 by the beta-lactam antibiotic, a process promoted by the N-carboxylated side chain of Lys392. We present evidence that, on acylation, the lysine side chain experiences a spontaneous decarboxylation that entraps the sensor in its activated state. Kinetic determinations and quantum mechanical/molecular mechanical calculations and the interaction networks in the crystal structure shed light on how this unprecedented process for activation of a receptor may be achieved and provide insights into the mechanistic features that differentiate the signal-transducing receptor from the structurally related class D beta-lactamases, enzymes of antibiotic resistance.
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Affiliation(s)
- Catherine Birck
- Département de Génomique et Biologie Structurales, IGBMC CNRS/INSERM/ULP, 1 rue Laurent Fries, BP 10142, 67404 - Illkirch CU Strasbourg, France
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