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  • 1
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Analysis of the initial interaction betweenEntamoeba histolytica trophozoites and the large intestine is impossible in humans and very difficult in experimental animals. To circumvent this obstacle we treated the luminal side of full-thickness rabbit colon segments mounted in Ussing-type chambers with trophozoite lysates of theE. histolytica HM1 virulent strain. Exposure to lysates for up to 90 min produced dose- and time-dependent effects on the colon, consisting of (a) increased decay rates for potential difference, short-circuit current, and transmural resistance and (b) mucosal damage ranging from vacuolation at the bases and shortening of epithelial cells to the loss of intercellular junctions, destruction of microvilli, and necrosis of interglandular epithelial zones. This acute model of intestinal amebiasis is sensitive, fast, and reliable.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-1955
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract   One of the main drawbacks of experimental amebiasis is the lack of an adequate animal model for invasive intestinal lesions. Mongolian gerbils are useful because both intestinal and hepatic amebiasis can be produced experimentally with Entamoeba histolytica trophozoites. In this paper we show results obtained with in vivo and in vitro models of intestinal amebiasis in gerbils. We inoculated gerbils intracecally with monoxenic cultures of a highly virulent E. histolytica HM1:IMSS substrain. In the in vivo model an increase in mucus production was observed during the first 6 h of interaction. Microulcerative mucosal lesions appeared at 24–72 h postinoculation. Inflammatory infiltrate and edema of the lamina propria were associated with superficial foci of necrosis. At 96 h the cecal mucosa had an almost normal appearance and live amebas were no longer detected. In the in vitro model, early damage was detected in cecal strips mounted in Ussing chambers as a rapid fall in potential difference, short-circuit current, and transepithelial resistance that correlated with the extent of the microscopic lesions produced. The latter consisted of cellular edema and the appearance of small, translucent vacuoles at the base of epithelial cells. Further damage led to loss of intercellular junctions, destruction of interglandular epithelial cells, and edema of the lamina propria. The present results demonstrate that the gerbil is useful as an experimental model for the analysis of early stages of invasive intestinal amebiasis both in vivo and in vitro.
    Type of Medium: Electronic Resource
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  • 3
    Publication Date: 2018-11-16
    Description: The study of the factors that have an influence on firm's export performance is one of the more fruitful lines of research in international marketing literature. However, there is no agreement among the researchers about which ones are the determinants that have an influence on the results of firms' exporting activity. In this sense, starting from the main reviewing studies on this topic, the purpose of this work consists on proposing a conceptual model that contains the main variables that have an influence on the export performance.
    Keywords: ddc:330 ; export Performance ; determinants ; international
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: Spanish
    Type: doc-type:article
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  • 4
    ISSN: 1574-6976
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In recent years, the incidence of fungal infections has been rising all over the world. Although the amount of research in the field of pathogenic fungi has also increased, there is still a need for the identification of reliable determinants of virulence. In this review, we focus on identified Candida albicans genes whose deletant strains have been tested in experimental virulence assays. We discuss the putative relationship of these genes to virulence and also outline the use of new different systems to examine the precise effect in virulence of different genes.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: We have previously shown that the plasmid-encoded toxin (Pet) of enteroaggregative Escherichia coli produces cytotoxic and enterotoxic effects. Pet-intoxicated epithelial cells reveal contraction of the cytoskeleton and loss of actin stress fibres. Pet effects require its internalization into epithelial cells. We have also shown that Pet degrades erythroid spectrin. Pet delivery within the intestine suggests that Pet may degrade epithelial fodrin (non-erythroid spectrin). Here we demonstrate that Pet has affinity for α-fodrin (formally named αII spectrin) in vitro and in vivo and cleaves epithelial fodrin, causing its redistribution within the cells. When Pet has produced its cytoskeletal effects, fodrin is found in intracellular aggregates as membrane blebs. Pet cleaves recombinant GST-fodrin, generating two breakdown products of 37 and 72 kDa. Sequencing of the 37 kDa fragment demonstrated that the cleavage site occurred within fodrin's 11th repetitive unit between M1198 and V1199, in the calmodulin binding domain. Site-directed mutagenesis of these amino acids prevented fodrin degradation by Pet. Pet also cleaves epithelial fodrin from cultured Pet-treated cells. A mutant in the Pet serine protease motif was unable to cause fodrin redistribution or to cleave GST-fodrin. This is the first report showing cleavage of α-fodrin by a bacterial protease. Cleavage occurs in the middle of the calmodulin binding domain, which leads to cytoskeleton disruption.
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  • 6
    ISSN: 1574-695X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Enteroaggregative Escherichia coli (EAEC) is an emerging cause of pediatric and adult travellers diarrhea. The mechanism by which EAEC induce diarrhea is not completely known. Two serine protease autotransporter proteins, named Pet and Pic have been identified in EAEC strains. Pet has enterotoxic and cytotoxic activities, while the role of Pic in pathogenesis may lie on its mucinolytic activity. Little is known about Pet and Pic biological activities in vivo. In this study the antibody responses against these autotransporter proteins in convalescent children is investigated. Fifteen (83%) children showed specific antibodies against Pet or Pic in their sera. IgG and IgM antibodies were the main isotype found. Specific antibodies against Pic, but not against Pet, were detected in sera from age-matched control group. These data show that specific anti-Pet and anti-Pic antibodies are produced during the course of a natural EAEC infection in children.
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  • 7
    ISSN: 0749-503X
    Keywords: Firefly luciferase ; yeast expression ; gene reporter ; Saccharomyces cerevisiae ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: The LUC gene coding for Photinus pyralis firefly luciferase was cloned in different yeast episomal plasmids in order to assess its possibilities as an in vivo reporter gene. Activity of the enzyme in transformed cells in vivo was measured by following light emission and assay conditions optimized in intact cells, with regard to oxygen concentration, temperature, cell concentration in assay mixtures and external ATP concentration. Among the factors tested, light emission was drastically influenced by the external pH in the assay (which resulted in a ten-fold amplification signal) and by substrate permeability. The growth phase of the cells was also important for the level of activity detected. Cloning of firefly luciferase gene under the control of different yeast-regulated promoters (ADH1, GAL1-10) enabled us to measure their strength which correlated well with previously described data. We conclude that firefly luciferase is an adequate gene reporter for the in vivo sensitive determination of gene expression and promoter strength in yeast.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Yeast 12 (1996), S. 1677-1702 
    ISSN: 0749-503X
    Keywords: Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: No Abstract
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0749-503X
    Keywords: Candida albicans ; HIS4 ; complementation ; molecular biology tools ; topological marker ; amino acid biosynthesis general control ; PEX5 ; Life and Medical Sciences ; Genetics
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Notes: We have isolated the Candida albicans HIS4 (CaHIS4) gene by complementation of a his4-34 Saccharomyces cerevisiae mutant. The sequenced DNA fragment contains a putative ORF of 2514 bp, whose translation product shares a global identity of 44% and 55% to the His4 protein homologs of S. cerevisiae and Kluyveromyces lactis, respectively. Analysis of CaHIS4 sequence suggests that, similarly to S. cerevisiae HIS4, it codes for a polypeptide having three separate enzymatic activities (phosphoribosyl-AMP cyclohydrolase, phosphoribosyl-ATP pyrophosphohydrolase and histidinol dehydrogenase) which reside in different domains of the protein. A C. albicans his4 strain is complemented with this gene when using a C. albicans-S. cerevisiae-Escherichia coli shuttle vector, thus enabling the construction of a host system for C. albicans genetic manipulation. In addition, upstream of the sequenced CaHIS4 sequence, we have found the 3′-terminal half of a gene encoding a PEX5-like protein. The EMBL/DDJB/GenBank Accession Number of this sequence is AJ003115. © 1998 John Wiley & Sons, Ltd.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2018-05-30
    Description: Most of articles that have recently appeared studying electronic service quality propose scales that are focused on measuring the quality of a particular service. However, could these scales be applied to measure the quality of other online services? In this situation, the main purpose of this study is to test the equivalence of a factor model to evaluate the quality of three services: online travel reservations, accommodation reservations and online ticketing. The results support the measurement equivalence of the measures. However, the importance of the dimensions varies across the services. In this sense, reliability is the most important factor in the evaluation of Websites of travel and accommodation reservations. Furthermore, in the evaluation of ticketing Websites, the higher weight factor is design.
    Keywords: ddc:650 ; electronic service quality ; measurement invariance ; multigroup ; confirmatory factor analysis ; Website
    Repository Name: EconStor: OA server of the German National Library of Economics - Leibniz Information Centre for Economics
    Language: English
    Type: doc-type:article
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