1,720,976 research outputs found
Sortase A promotes virulence in experimental Staphylococcus lugdunensis endocarditis.
No full textStaphylococcus lugdunensis is a commensal of humans and an opportunistic pathogen. It can cause an aggressive form of infective endocarditis in healthy humans akin to Staphylococcus aureus. Here we compared the virulence of the genome-sequenced S. lugdunensis strain N920143 to S. aureus in an experimental rat endocarditis model. N920143 caused a milder course of disease with lower levels of bacteraemia and smaller endocardial vegetations than S. aureus strain Newman. However, vegetations were comparable to those produced by S. aureus MRSA strain COL. Little is known about virulence factors of S. lugdunensis as systems to manipulate the bacterium genetically are currently limited. Here, we report a method for electroporation of S. lugdunensis with plasmid DNA and demonstrate that the low efficiency of transformation is due to the activity of a conserved type I restriction-modification system. To streamline the transformation process, we constructed SL01B, an E. coli strain expressing the hsdM/hsdS genes of N920143. Modified plasmid DNA isolated from SL01B transformed S. lugdunensis strains from clonal complexes 1 and 2 efficiently. A deletion mutant of N920143 lacking sortase A was significantly less virulent than the wild-type in the endocarditis model. Mutants defective in single surface proteins Fbl or vWbl were not significantly different from the wild-type but showed trends towards reduced virulence
Iron regulated surface determinant (Isd) proteins of Staphylococcus lugdunensis.
No full textStaphylococcus lugdunensis is the only species of coagulase negative staphylococcus with a locus encoding iron regulated surface determinant (Isd) proteins. In S. aureus the Isd proteins capture haem from haemoglobin, transfer it across the wall to a membrane-bound transporter which delivers it into the cytoplasm where haem oxygenases release iron. The Isd proteins of S. lugdunensis are expressed under iron-restricted conditions. We propose that S. lugdunensis IsdB and IsdC proteins perform the same functions as those of S. aureus. S. lugdunensis IsdB is the only haemoglobin receptor within the isd locus. It specifically binds human haemoglobin with a K(D) of 23 nM and transfers haem on IsdC. IsdB expression promotes bacterial growth in an iron-limited medium containing human haemoglobin but not mouse haemoglobin. This correlates with weak binding of IsdB to mouse haemoglobin in vitro. Unlike IsdB and IsdC, IsdJ and IsdK are not sorted to the cell wall in S. lugdunensis. In contrast, IsdJ expressed in S. aureus and Lactococcus lactis is anchored to peptidoglycan, suggesting that S. lugdunensis sortases may differ in signal recognition or could be defective. IsdJ and IsdK are present in the culture supernatant suggesting they could acquire haem from the external milieu. The IsdA protein of S. aureus protects bacteria from bactericidal lipids due to its hydrophilic C-terminal domain. IsdJ has a similar region and protected S. aureus and L. lactis as efficiently as IsdA but, possibly due to its location, was less effective in its natural host
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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