1,720,953 research outputs found
Molecular epidemiology of Listeria monocytogenes: genotyping, molecular serotyping and expression profiles analysis of genes involved in pathogenesis and virulence mechanisms
No full textListeria monocytogenes è un patogeno intracellulare responsabile di severe infezioni caratterizzate da un elevato tasso di letalità, soprattutto in soggetti con deficit del sistema immunitario. Data la diffusa presenza e l’estrema variabilità nella virulenza dei ceppi, molteplici tecniche molecolari sono utilizzate per individuare le differenze esistenti all’interno della specie. In questo studio, 250 ceppi di L. monocytogenes di differente origine sono stati caratterizzati mediante single Enzyme Amplified Fragment Length Polymorphism (sAFLP). Un sottogruppo rappresentativo di 50 ceppi è stato selezionato per confrontare l’elettroforesi su gel di agarosio, prevista dalla metodica, con la separazione microfluidica automatizzata (sistema ExperionTM) su chip. Inoltre, altri 109 ceppi di Listeria spp. sono stati analizzati per standardizzare un nuovo saggio in Real-time, basato su due Triplex-PCR con sonde TaqMan, per l’individuazione dei sierogruppi i cui risultati sono stati confrontati con il metodo molecolare di riferimento. Infine, è stata valutata, mediante qRT-PCR, l’espressione di geni di resistenza a stress e dei principali fattori di virulenza in 20 isolati da alimenti e casi clinici. In particolare, è stato valutato l’effetto di concentrazioni sub-letali (10 ppm) di cloruro di benzalconio sull’espressione di sigB (fattore sigma alternativo di risposta a stress), mdrL e lde (pompe di efflusso) e orfA (ipotetico repressore di mdrL). In parallelo, è stata valutata l’attività antibatterica del disinfettante secondo la UNI EN 1276/2000. Per gli stessi isolati sono stati anche determinati i livelli di espressione dei geni codificanti le internaline A e B (inlA, inlB), la listeriolisina O (hly), il regolatore trascrizionale (prfA) di LIPI-1 e l’idrolasi dei sali biliari (bsh). La genotipizzazione mediante sAFLP ha permesso di identificare 13 clusters, rappresentativi di due gruppi principali distinti e concordanti con la classificazione in Lineage e con i dati epidemiologici di prevalenza dei sierotipi responsabili di infezioni umane e della contaminazione di alimenti. La sAFLP si è rivelata una metodica accurata e altamente discriminante per la genotipizzazione del patogeno, anche in combinazione con l’elettroforesi microfluidica, la quale ha fornito risultati analoghi al metodo tradizionale con una migliore risoluzione nella visualizzazione delle bande. Il sistema ExperionTM richiede quantità inferiori di campione, evita l’impiego di reagenti tossici e riduce sensibilmente i tempi di analisi, rappresentando un valido supporto per la caratterizzazione del patogeno mediante sAFLP. La sierotipizzazione molecolare in Real-time PCR ha confermato la precedente classificazione in sierogruppi, permettendo la separazione dei sierotipi 1/2a, 1/2b, 1/2c e 4b, implicati in oltre il 90% di casi umani e di contaminazione di alimenti, in quattro gruppi distinti. Il metodo proposto risulta accurato e riproducibile e può contribuire all’implementazione delle misure di sorveglianza epidemiologica per il controllo della listeriosi. Il cloruro di benzalconio è risultato efficace nel 70% dei ceppi analizzati, soprattutto negli isolati umani e ha influenzato l’espressione dei geni target. Differenze significative (p<0,05) sono state osservate nei livelli di trascrizione di mdrL e sigB in seguito al trattamento con disinfettante. In tutti gli isolati da alimenti risultati resistenti, sono emersi livelli di espressione più elevati di sigB, mdrL e lde. L’attivazione di sistemi di efflusso può portare ad un aumento della resistenza dei ceppi non solo verso il cloruro di benzalconio, ma anche contribuire allo sviluppo di fenomeni di resistenza crociata con antibiotici. Maggiori livelli di espressione di inlB, hly, prfA e bsh sono stati osservati nei ceppi umani, al contrario di quelli di inlA più elevati negli isolati da alimenti. Tuttavia, i valori massimi di inlA hanno riguardato due ceppi clinici, in cui sono emersi livelli di espressione elevati per tutti i geni target, facendone ipotizzare un maggiore potenziale di virulenza. Una correlazione molto significativa è stata osservata tra i livelli di espressione di inlA e inlB e in misura minore tra prfA e bsh, in accordo con i dati di letteratura. Dall’analisi delle curve di melting sono emerse differenze significative (≤0,001) tra gli isolati della Lineage I (1/2b, 4b) rispetto alla II (1/2a, 3a, 1/2c) per i geni mdrL, lde, inlA, prfA, bsh, suggerendo una probabile diversità di sequenza. La comprensione dei meccanismi molecolari e la caratterizzazione dei ceppi potenzialmente più virulenti sono aspetti fondamentali per il controllo della listeriosi, in quanto consentono di migliorare la sorveglianza e la prevenzione del rischio associato a L. monocytogenes per la salute umana.Listeria monocytogenes is a intracellular bacterium widely distributed in the environment that causes severe diseases with a high fatality rate especially in immunocompromised individuals.
Several molecular techniques have been developed for strains characterization because significant differences in the virulence profile of isolates have been demonstrated.
In this study, L. monocytogenes strains (n=250) from different sources were analysed by single Enzyme Amplified Fragment Length Polymorphism (sAFLP). A representative subgroup was selected to compare the traditional gel electrophoresis with a chip-based microfluidic system (ExperionTM). Moreover, additional Listeria spp. isolates (n=109) were selected to standardize a new assay for serogroup identification in Real-time by using two different TaqMan-based Triplex-PCR and the results were compared with molecular reference method. Furthermore, by qRT-PCR, the expression levels of stress response and virulence genes were evaluated in isolates (n=20) from foods and human listeriosis. Particularly, the effects of sub-lethal concentration of benzalkonium chloride (10 ppm) on the expression profiles of sigB (stress-response sigma factor), mdrL and lde (efflux pumps), and orfA (putative mdrL repressor) were assessed. The antimicrobial activity of benzalkonium chloride (BC) was also investigated according to UNI EN 1276/2000. Finally, the expression levels of genes encoding the internalins A and B (inlA, inlB), Listeriolysin O (hly), the LIPI-1 transcriptional regulator (prfA), and bile salt hydrolase (bsh) were determined.
Genotyping by sAFLP allowed to identify 13 clusters, included in two well defined groups and in agreement to the Lineage classification and epidemiological data on the prevalence of most common serotypes involved in human illness and foodstuffs contamination. The sAFLP has proved to be an accurate method with high discriminatory power for L. monocytogenes typing and its epidemiological usefulness was further confirmed in combination with automated microfluidic electrophoresis system, requiring lower samples volume and time analysis.
Molecular serogrouping by Real-time PCR confirmed previous classification into four groups and allowed a rapid discrimination of 1/2a, 1/2b, 1/2c, and 4b serotypes, recognized in more than 90% of food and patients isolates. Therefore, the new approach can improve routine surveillance of listeriosis and epidemiological investigations. The benzalkonium chloride showed the antimicrobial activity in 70% of strains, particularly in human isolates and affected the target genes expression. Adaptation to BC determined a significant (p<0,05) overexpression of mdrl and sigB. All less sensitive food isolates showed the highest sigB, mdrL, and lde transcription levels. The efflux pumps could play a role in BC-resistance and the sub-lethal exposure to antimicrobial agent can lead cross-resistance between antibiotics and disinfectants.
The expression levels of inlB, hly, prfA and bsh were higher in clinical than in food strains, except for inlA. However, the maximum levels of inlA were found in two human strains which also showed high levels of all virulence genes. A significant correlation between inlA and inlB expression was observed as between prfA and bsh, according to other studies. Furthermore, relevant differences (≤0,001) between Lineage I (1/2b, 4b) and II (1/2a, 3a, 1/2c) strains were found in mdrL, lde, inlA, prfA, and bsh melting temperature, suggesting the presence of mutations in genomic sequence. The characterization of more virulent strains and the comprehension of molecular mechanisms are essential for the epidemiological surveillance and the risk assessment of human listeriosis.Dottorato di ricerca in Scienze per la salute (XXIV ciclo
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
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
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