1,720,955 research outputs found
Rapid aggregation of Staphylococcus aureus in synovial fluid is influenced by synovial fluid concentration, viscosity, and fluid dynamics-with evidence of polymer bridging
No full textEarly bacterial survival in the post-surgical joint is still a mystery. Recently, synovial fluid-induced aggregation was proposed as a potential mechanism of bacterial protection upon entry into the joint. As synovial fluid is secreted back into the joint cavity following surgery, rapid fluctuations in synovial fluid concentration, composition, and viscosity occur. These changes, along with fluid movement from post-operative joint motion, will modify the environment and potentially affect the kinetics of aggregate formation. Through this work, we sought to evaluate the influence of exposure time, synovial fluid concentration, viscosity, and fluid dynamics on aggregation. Furthermore, we aimed to elucidate the primary mechanism of aggregate formation by assessing the interaction of bacterial adhesins with synovial fluid polymer, fibrinogen. Following incubation in each simulated post-operative joint condition, the aggregates were imaged using confocal microscopy. Our analysis revealed the formation of two distinct aggregate phenotypes dependent on whether the incubation was conducted under static or dynamic conditions. Using a surface adhesin mutant, we have narrowed down the genetic determinants for synovial fluid aggregate formation and identified essential host polymers required. We report here that synovial fluid-induced aggregation is influenced by various changes specific to the post-surgical joint environment. While we now have evidence that select synovial fluid polymers facilitate bridging aggregation through essential bacterial adhesins, we suspect that their utility is limited by the increasing viscosity under static conditions. Furthermore, dynamic fluid movement recovers the ability of the bacteria with present surface proteins to aggregate under high viscosity conditions, yielding large, globular aggregates
Synovial fluid-induced aggregation occurs across Staphylococcus aureus clinical isolates and is mechanistically independent of attached biofilm formation
No full textRapid synovial fluid-induced aggregation of Staphylococcus aureus is currently being investigated as an important factor in the establishment of periprosthetic joint infections (PJIs). Pathogenic advantages of aggregate formation have been well documented in vitro, including recalcitrance to antibiotics and protection from host immune defenses. The objective of the present work was to determine the strain dependency of synovial fluid-induced aggregation by measuring the degree of aggregation of 21 clinical S. aureus isolates cultured from either PJI or bloodstream infections using imaging and flow cytometry. Furthermore, by measuring attached bacterial biomass using a conventional crystal violet assay we assessed whether there is a correlation between the aggregative phenotype and surface-associated biofilm formation. While all of the isolates were stimulated to aggregate upon exposure to bovine synovial fluid (BSF) and human serum (HS), the extent of aggregation was highly variable between individual strains. Interestingly, the PJI isolates aggregated significantly more upon BSF exposure than those isolated from bloodstream infections. While we were able to stimulate biofilm formation with all of the isolates in growth media, supplementation with either synovial fluid or human serum inhibited bacterial surface attachment over a 24-hour incubation. Surprisingly, there was no correlation between the degree of synovial fluid-induced aggregation and quantity of surface-associated biofilm as measured by a conventional biofilm assay without host fluid supplementation. Taken together, synovial fluid-induced aggregation appears to be widespread among S. aureus strains and mechanistically independent of biofilm formation
In vitro staphylococcal aggregate morphology and protection from antibiotics is dependent on distinct mechanisms arising from postsurgical joint components and fluid motion
No full textConsiderable progress has been made toward elucidating the mechanism of Staphylococcus aureus aggregation in synovial fluid. In this study, aggregate morphology was assessed following incubation in several simulated postsurgical joint conditions. Using fluorescently labeled synovial fluid polymers, we show that aggregation occurs through two distinct mechanisms: direct bridging between S. aureus cells and host fibrinogen, and an entropy-driven depletion mechanism facilitated by hyaluronic acid and albumin. By screening surface adhesin deficient mutants (clfA, clfB, fnbB, and fnbA), we identified the primary genetic determinant of aggregation in synovial fluid to be Clumping factor A. To characterize this bridging interaction, we employed an atomic force microscopy- based approach to quantify the binding affinity of either wild type S. aureus or the adhesin mutant to immobilized fibrinogen. Surprisingly, we found there to be cell-to-cell variability in the binding strength of the bacteria to immobilized fibrinogen. Super high resolution microscopy imaging revealed that fibrinogen binding to the cell wall is heterogeneously distributed at both the single cell and population level. Finally, we assessed the antibiotic tolerance of various aggregate morphologies arising from newly deciphered mechanisms of polymer-mediated synovial fluid-induced aggregation. The formation of macroscopic aggregates under shear, were highly tolerant of gentamicin, while smaller aggregates, formed under static conditions were susceptible. We hypothesize that aggregate formation in the joint cavity, in combination with shear, is mediated by both polymer-mediated aggregation mechanisms, with depletion forces enhancing the stability of essential bridging interactions. <br/
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Full text link“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
Full text linkWe 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
Full text linkWe 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
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