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Patrice Courvalin - One of the best experts on this subject based on the ideXlab platform.
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Evolution of glycopeptide resistance.
Evolutionary Biology of Bacterial and Fungal Pathogens, 2008Co-Authors: Patrice CourvalinAbstract:This chapter briefly reviews the mode of action and the mechanism of bacterial resistance to glycopeptides, as exemplified by the VanB type, and discusses its diversity, regulation, evolution, origin, and recent dissemination to methicillin-resistant Staphylococcus aureus. Classification of glycopeptide resistance is based on the primary sequence of the structural genes for the resistance ligases. Although the six types of resistance involve related enzymic functions, they can be distinguished by the location of the corresponding genes and by the mode of regulation of gene expression. An interesting phenomenon that has developed in some VanB- and VanA-type enterococci is vancomycin dependence. These glycopeptide-dependent strains are also able to grow in the absence of glycopeptides if supplied with the dipeptide D-Ala-D-Ala, confirming that they are unable to produce the ligase encoded by the chromosomal ddl gene. The vanF operon is composed of five genes (vanYF, vanZF, vanHF, vanF, and vanXF) encoding homologues of VanY, VanZ, VanH, VanA, and VanX, and the genes essential for resistance (vanHF, vanF, and vanXF) are organized and oriented as in VanA-type strains. The evolutionary lineage of these groups of homologous genes is not clear, but they may have a common ancestor, or Paenibacillus could be a progenitor of the resistance operons acquired by enterococci. Conjugal transfer of plasmids that have acquired Tn1546-like elements by transposition appears to be responsible for the spread of glycopeptide resistance in enterococci.
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Vane a new type of acquired glycopeptide resistance in enterococcus faecalis bm4405
Antimicrobial Agents and Chemotherapy, 1999Co-Authors: Marguerite Fines, Bruno Perichon, Peter E Reynolds, Daniel F Sahm, Patrice CourvalinAbstract:Enterococcus faecalis BM4405 was resistant to low levels of vancomycin (MIC, 16 μg/ml) and was susceptible to teicoplanin (MIC, 0.5 μg/ml). No PCR product was obtained when the total DNA of this clinical isolate was used as a template with primers specific for glycopeptide resistance genes vanA, vanB, vanC, and vanD. However, a 604-bp PCR fragment was obtained when V1 and V2 degenerate primers were used and total DNA was digested with HindIII as a template. The product was cloned and sequenced. The deduced amino acid sequence had greater identity (55%) with VanC than with VanA (45%), VanB (43%), or VanD (44%). This was consistent with the fact that BM4405 synthesized peptidoglycan precursors that terminated in d-serine residues. After induction with vancomycin, weak d,d-dipeptidase and penicillin-insensitive d,d-carboxypeptidase activities were detected in cytoplasmic extracts of BM4405, whereas a serine racemase activity was found in the membrane preparation. This new type of acquired glycopeptide resistance was named Vane.
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regulation of vanb type vancomycin resistance gene expression by the vans b vanr b two component regulatory system in enterococcus faecalis v583
Journal of Bacteriology, 1996Co-Authors: Stefan Evers, Patrice CourvalinAbstract:Acquired VanA- and VanB-type glycopeptide resistance in enterococci is due to synthesis of modified peptidoglycan precursors terminating in D-lactate. As opposed to VanA-type strains which are resistant to both vancomycin and teicoplanin, VanB-type strains remain teicoplanin susceptible. We have determined the sequence of a 7,160-bp DNA fragment associated with VanB-type resistance in Enterococcus faecalis V583 that contains seven open reading frames. The distal part encoded the VanH (B), VanB, and VanX (B) proteins that are highly similar to the putative VanH, VanA, and VanX proteins responsible for VanA-type resistance. Upstream from the structural genes for these proteins were the vanY(B) gene encoding a D,D-carboxypeptidase and an open reading frame vanW with an unknown function. The proximal part of the gene cluster coded for the apparent VanS(B)-VanR (B) two-component regulatory system. VanR (B) was related to response regulators of the OmpR subclass, and VanS (B) was related to membrane-associated histidine protein kinases. Analysis of transcriptional fusions with a reporter gene and promoter mapping indicated that the VanR B-VanS B two-component regulatory system activates a promoter located immediately downstream from the vanS B gene. Vancomycin, but not teicoplanin, was an inducer, which explains teicoplanin susceptibility of VanB-type enterococci.
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Purification and characterization of the VanB ligase associated with type B vancomycin resistance in Enterococcus faecalis V583
FEBS Letters, 1994Co-Authors: Djalal Meziane-cherif, Patrice Courvalin, Marie-ange Badet-denisot, Stefan Evers, Bernard BadetaAbstract:Acquired resistance to glycopeptides in enterococci is associated with the production of D‐Alanine: D‐Alanine ligase‐related proteins. The VanA protein associated with high‐level vancomycin and teicoplanin resistance (VanA phenotype) synthesizes a new peptidoglycan precursor, D‐alanine‐D‐lactate, that has reduced glycopeptide affinity. Production of a similar protein, VanB, is induced in strains that display variable levels of vancomycin resistance but remain susceptible to teicoplanin (VanB phenotype). This paper describes the over‐production, purification and characterization of VanB. Comparison of kinetic parameters of the two Van enzymes suggests that differences in catalytic efficiency could account, at least in part, for the various levels of vancomycin resistance.
Emre Arabaci - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of a novel hinged Vane rotary turbine – part I: The effect of different Vane thickness and Vane weight on turbine performance
International Journal of Refrigeration, 2015Co-Authors: Melih Okur, Emre ArabaciAbstract:Abstract The structure of newly designed turbo rotary Pars turbine shows similarities with the structure of commercially available Vane compressors. The Vane is embedded within the turbine mainframe whereas the other end is hinged to the rotor liner. Friction loads and pressure leaks occur in the Vane side surface during the operation of the turbine. Therefore, design studies that reduce the friction losses and pressure leaks of the Vane which improves turbine performance. In this study, the effects of friction and pressure leakages on the performance of the turbine have been investigated. Vane thickness size has been changed. Three different sizes (thick, standard and thin Vanes) have been experimentally investigated. The experiments are also repeated by reducing the Vane weights without making any changes on the outer geometry of the thick and standard Vane. As a result of the experiments, 75% more power of the turbine has been obtained for the thin Vane.
Melih Okur - One of the best experts on this subject based on the ideXlab platform.
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Experimental study of a novel hinged Vane rotary turbine – part I: The effect of different Vane thickness and Vane weight on turbine performance
International Journal of Refrigeration, 2015Co-Authors: Melih Okur, Emre ArabaciAbstract:Abstract The structure of newly designed turbo rotary Pars turbine shows similarities with the structure of commercially available Vane compressors. The Vane is embedded within the turbine mainframe whereas the other end is hinged to the rotor liner. Friction loads and pressure leaks occur in the Vane side surface during the operation of the turbine. Therefore, design studies that reduce the friction losses and pressure leaks of the Vane which improves turbine performance. In this study, the effects of friction and pressure leakages on the performance of the turbine have been investigated. Vane thickness size has been changed. Three different sizes (thick, standard and thin Vanes) have been experimentally investigated. The experiments are also repeated by reducing the Vane weights without making any changes on the outer geometry of the thick and standard Vane. As a result of the experiments, 75% more power of the turbine has been obtained for the thin Vane.
Martti Vaara - One of the best experts on this subject based on the ideXlab platform.
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vana and vanb incorporate into an endemic ampicillin resistant vancomycin sensitive enterococcus faecium strain effect on interpretation of clonality
Journal of Clinical Microbiology, 1999Co-Authors: J Suppola, Elina Kolho, Saara Salmenlinna, Eveliina Tarkka, Jaana Vuopiovarkila, Martti VaaraAbstract:Clonal spread and horizontal transfer in the spread of vancomycin resistance genes were investigated. Multiplex PCR, pulsed-field gel electrophoresis (PFGE), hybridization of enterococcal plasmids with the vanA and vanB probes, and sequencing of a fragment of vanB were used in the analysis. Before May 1996, 12 vancomycin-resistant Enterococcus faecium (VRE) isolates were found in Finland. Between May 1996 and October 1997, 156 VRE isolates were found in the Helsinki area. Between December 1997 and April 1998, fecal samples from 359 patients were cultured for VRE. One new case of colonization with VRE was found. During the outbreak period, 88% (137 of 155) of the VRE isolates belonged to two strains (VRE types I and II), as determined by PFGE. Each VRE type I isolate possessed vanB, and five isolates also had vanA. Of the 34 VRE type II isolates, 27 possessed vanA and 7 possessed vanB. Fifteen of 21 (71%) ampicillin-resistant, vancomycin-sensitive E. faecium (VSE) isolates found during and after the outbreak period in one ward were also of type II. Two VSE type II isolates were found in the hospital before the outbreak in 1995. By PFGE, the three groups (vanA, vanB, or no van gene) of type II shared the same band differences with the main type of VRE type II with vanA. None of the differences was specific to or determinative for any of the groups. Our material suggests that vanA and vanB incorporate into an endemic ampicillin-resistant VSE strain.
Andrew D. Ketsdever - One of the best experts on this subject based on the ideXlab platform.
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Effect of Vane thickness on radiometric force
Journal of Fluid Mechanics, 2013Co-Authors: Austin L. Ventura, Natalia Gimelshein, Sergey Gimelshein, Andrew D. KetsdeverAbstract:A numerical and experimental study of radiometric forces on Vanes of different thickness is presented for the flow regime where the radiometric force is near its maximum. For single- and multi-Vane geometries, it is shown that radiometric force decreases by only ∼10–15 % when the Vane thickness-to-height ratio increases fourfold from 0.5 to 2. For a single-Vane geometry, the shear force on the lateral side of the Vane is attributed to a vortex flow generated by the interaction of cold chamber walls and heated walls of the Vane. In that case, it always acts to reduce the total radiometric force governed by the pressure difference between the hot and the cold sides of the Vane. For a multi-Vane geometry, represented by a perforated Vane, the shear force becomes positive for larger thickness-to-height ratios and lower pressures, primarily due to strong Vane-driven transpiration flow through the gaps.
