1,720,954 research outputs found
Survival and recovery of Escherichia coli O157:H7 during starvation at sub-optimal temperatures
No full textEscherichia coli O157:H7 is an important foodborne pathogen with a dual lifestyle of growth within a host and persistence in non-host environments. Environmental survival of E. coli O157:H7 is particularly important in New Zealand due to the increasing trend in notified clinical cases, with most being associated with rural environments rather than contaminated regulated foods. Starvation and a decrease in temperature are characteristic of the conditions encountered by bacteria during transition from a reservoir host, normally a ruminant, to the environment; cf. feast to famine. These conditions are known to induce bacterial entrance into the viable but non-culturable (VBNC) state where cell viability can only be detected using culture-independent methods with the number of colonies recovered decreasing over the duration of the starvation period. Findings from this study showed that formation of a VBNC sub-population can be induced by starving E. coli O157:H7 at sub-optimal temperatures.
Five E. coli O157:H7 strains were used in this study; NCTC12900 as a reference strain, three New Zealand clinical isolates and a New Zealand bovine isolate. Cells were starved in phosphate buffered saline for 84 days at sub-optimal temperatures. Cell viability was determined using the SYTO 9-PI staining system coupled with a haemocytometer counting method developed in this study. Cell culturability was assessed using the nutrient-rich tryptic soy agar (TSA), nutrient-limited plate count agar (PCA), and PCA with additional supplements. The distribution of colony size provided information on the population dynamics of starved cells and their ability to recover on agar. The role of quorum sensing (LuxS/autoinducer-2) on starved cell recovery was investigated by supplementing PCA with quorum sensing molecules and using a mutant strain deficient in luxS, a gene encoding the synthase of autoinducer-2. The ability of starved and non-starved cells to metabolise single carbon sources were compared using the Biolog MicroPlatesTM.
When held at 4°C, a three- to six-log reduction in culturability on PCA was observed after 84 days of starvation. The reduction in culturability observed for cells starved at 15°C was between one to two logs on PCA. Despite the decline in culturability on PCA, the number of viable cells as determine by LIVE/DEAD® BacLightTM staining remained within one log of the initial viable count. Supplementation of PCA with 0.2% sodium pyruvate resulted in a significant increase in the number of colonies recovered from 4°C-starved cultures for all E. coli O157:H7 strains tested. Recovery on TSA was consistently at least two-logs higher than recovery on PCA for E. coli O157:H7 cells after 84 days of starvation at 4°C. The distribution of colony diameter was markedly wider for 4°C-starved cells compared to non-starved cells when recovered under aerobic conditions. In addition to the strain variation observed, culturability of starved E. coli O157:H7 was found to be dependent on the starvation temperature, the nutrient level of recovery media, and the presence of specific resuscitation factors such as pyruvate. While the culturability phenotype was similar between reference, clinical and bovine E. coli O157:H7 strains, metabolic profiles determined using carbon source MicroPlatesTM differed. Analysis of the carbon utilisation kinetics allowed comparison of carbon metabolism between exponential phase, stationary phase and starved E. coli O157:H7. The duration of lag in substrate utilisation was significantly different between starved and non-starved cells. Supplementing PCA with quorum sensing molecules and using a mutant strain deficient in luxS, a gene encoding the synthase of autoinducer-2, did not result in a significant improvement in the recovery of starved VBNC cells.
Based on current knowledge, models for the change in E. coli O157:H7 population dynamics during its lifecycle, the role of pyruvate resuscitation of VBNC cells, and factors involved in E. coli O157:H7 infection of bovine and human hosts were proposed. The ability of New Zealand clinical and bovine isolates to enter the VBNC state, which was demonstrated in this study, highlighted the potential for culture-based assessment methods to underestimate the number of viable E. coli O157:H7. While reports of the use of pyruvate for resuscitating VBNC cells are in the literature, this study is the first to propose a mechanism of pyruvate resuscitation. By understanding the physiology of VBNC cells and mechanism of their resuscitation, it may be possible to eliminate the potential for underestimation of viable E. coli O157:H7 in the environment and in food by tailoring culture methods to promote their growth
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
Author Under Sail The Imagination of Jack London, 1893-1902
No full textIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Intro -- Title Page -- Copyright Page -- Dedication -- Contents -- Acknowledgments -- Introduction -- 1. Spirit Truth -- 2. From Absorption to Theatricality and Back Again -- 3. "I Will Build a New Present" -- 4. Sons as Authors -- 5. Fathers as Publishers -- 6. The Daughter as Author -- 7. Lovers as Authors -- 8. At Sea with the Family -- 9. Yellow News, Yellow Stories -- 10. The Return Home -- Notes -- Bibliography -- Index -- About Jay WilliamsIn Author Under Sail, Jay Williams offers the first complete literary biography of Jack London as a professional writer engaged in the labor of writing. It examines the authorial imagination in London's work, the use of imagination in both his fiction and nonfiction, and the ways he defined imagination in the creative process in his business dealings with his publishers, editors, and agents. In this first volume of a two-volume biography, Williams traverses the years 1893 to 1902, from London's "Story of a Typhoon" to The People of the Abyss. The Jack London who emerges in the pages of Author Under Sail is a writer whose partnership with publishers, most notably his productive alliance with George Brett of Macmillan, was one of the most formative in American literary history. London pioneered many author models during the heyday of realism and naturalism, blurring the boundaries of these popular genres by focusing on absorption and theatricality and the representation of the seen and unseen. London created an impassioned, sincere, and extremely personal realism unlike that of other American writers of the time. Author Under Sail is a literary tour de force that reveals the full range of London as writer, creative citizen, and entrepreneur at the same time it sheds light on the maverick side of machine-age literature.Description based on publisher supplied metadata and other sources.Electronic reproduction. Ann Arbor, Michigan : ProQuest Ebook Central, YYYY. Available via World Wide Web. Access may be limited to ProQuest Ebook Central affiliated libraries
- …
