1,720,987 research outputs found
AcrAB efflux pump impacts on the survival of adherent-invasive Escherichia coli strain LF82 inside macrophages
Full text linkThe tripartite complex AcrAB-TolC is the major RND pump in Escherichia coli and other Enterobacteriaceae. It consists of the AcrB transporter, which is embedded in the inner membrane, the AcrA adapter located in the periplasm, and the channel protein TolC responsible for the transport of substrates towards the extracellular environment. Besides conferring resistance to many classes of antibiotics, AcrAB plays a role in the pathogenesis and virulence of several bacterial pathogens. Here we report that the AcrAB pump heavily affects the infection process of the LF82 strain, the prototype of Adherent-Invasive Escherichia coli (AIEC) which are highly abundant in the ileal mucosa of Chron disease patients. We found that the deletion of genes encoding AcrA and/or AcrB leads to decreased survival of LF82 within macrophages. Ectopic AcrAB expression in a acrAB defective mutant restores the wild type condition. Furthermore, we demonstrate that inhibition of AcrB and replacement of the transporter with an unfunctional AcrB also interfere with bacterial viability inside macrophages. Overall, these data suggest a pivotal role of the AcrAB efflux pump in bacteria-host cell interactions also in AIEC
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
Stenotrophomonas maltophilia isolated from patients affected by cystic fibrosis: genotyping analysis and molecular characterisation of virulence determinants
No full textThe virF promoter in Shigella: more than just a curved DNA stretch
No full textIn the human enteropathogen Shigella transcription of virF, the primary regulator of the invasion functions, is strictly temperature-dependent and is antagonistically mediated by H-NS and FIS, which bind to specific sites on the virF promoter. Here we report on the relevance of DNA geometry to the themoregulation of virF and demonstrate that the virF promoter hosts a major DNA bend halfway between two H-NS sites. The bent region has been mutagenized in vitro to mimic temperature-induced changes of DNA curvature. Functional analysis of curvature mutants and of promoter constructs in which the two H-NS sites are phased-out by a half-helix turn reveals that modifying the spatial relationships between these sites severely affects the Interaction of H-NS with the virF promoter, as well as its in vivo and in vitro temperature-dependent activity. The role of promoter curvature as thermosensor is also compatible with the present observation that, with increasing temperature, the virF bending centre moves downstream at a rate having its maximum around the transition temperature, abruptly unmasking a binding site for the transcriptional activator FIS
Modulation of omv production by the lysis module of the dlp12 defective prophage of Escherichia coli k12
Full text linkOuter membrane vesicles (OMVs) are nanostructures mostly produced by blebbing of the outer membrane in Gram negative bacteria. They contain biologically active proteins and perform a variety of processes. OMV production is also a typical response to events inducing stress in the bacterial envelope. In these cases, hypervesiculation is regarded as a strategy to avoid the dangerous accumulation of undesired products within the periplasm. Several housekeeping genes influence the biogenesis of OMVs, including those correlated with peptidoglycan and cell wall dynamics. In this work, we have investigated the relationship between OMV production and the lysis module of the E. coli DLP12 cryptic prophage. This module is an operon encoding a holin, an endolysin and two spannins, and is known to be involved in cell wall maintenance. We find that deleting the lysis module increases OMV production, suggesting that during evolution this operon has been domes-ticated to regulate vesiculation, likely through the elimination of non‐recyclable peptidoglycan frag-ments. We also show that the expression of the lysis module is negatively regulated by environmental stress stimuli as high osmolarity, low pH and low temperature. Our data further highlight how defective prophages finely contribute to bacterial host fitness
A multifactor regulatory circuit involving H-NS, VirF and an antisense RNA modulates transcription of the virulence gene icsA of Shigella flexneri.
No full textVariations 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
Diffusible signal factors (DSFs) bind and repress VirF, the leading virulence activator of Shigella flexneri
Full text linkShigella, the aetiological agent of human bacillary dysentery, controls the expression of its virulence determinants through an environmentally stimulated cascade of transcriptional activators. VirF is the leading activator and is essential for proper virulence expression. In this work, we report on in vitro and in vivo experiments showing that two autoinducers of the DSF family, XcDSF and BDSF interact with the jelly roll module of VirF causing its inhibition and affecting the expression of the entire virulence system of Shigella, including its ability to invade epithelial cells. We propose a molecular model explaining how the binding of XcDSF and BDSF causes inhibition of VirF by preventing its dimerization. Overall, our experimental results suggest that XcDSF and BDSF may contribute to ”colonisation resistance” in the human gut or, alternatively, may be exploited for the fine-tuning of Shigella virulence expression as the bacterium migrates from the lumen to approach the intestinal mucosa. Our findings also stress how a detailed understanding of the interaction of DSF ligands with VirF may contribute to the rational development of innovative antivirulence drugs to treat shigellosis
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
- …
