1,721,080 research outputs found
Internalization mechanisms of biopolymeric nanoparticles in plants and fungi and application in integrated pest management
Full text linkThe application of biodegradable poly lactic-co-glycolic acid nanoparticles (PLGA-NPs) to develop controlled release systems of bioactive molecules has shown enormous potential in agriculture. PLGA is a non toxic harmless biocompatible polymer that degrades into nontoxic byproducts. The hydrolysis of lactide and glycolide monomers leads to lactic and glycolic acids, respectively, which are metabolized by the Krebs cycle releasing carbon dioxide and water. The main advantage of nanoformulations consists in protecting the load from volatilization, infiltration, outflow, leaching and photo-, chemio- or bio-degradation. The expected benefit could be a decrease in the amount of active chemicals incorporated into plants and soils, and a low environmental impact. However, the use of PLGA-NPs in agriculture needs an accurate evaluation of nanoparticle-plant interactions, including the comprehension of the mechanisms of their uptake, translocation and accumulation.
In this PhD project, PLGA-NPs were used for a dual purpose. The first one was to clarify the mechanisms of internalization of PLGA-NPs, sorting and targeting into plant and fungal cells according to morphology and physico-chemical properties of NPs. The second one was to use NPs as vectors to deliver antifungal molecules against plant pathogenic fungi cause of immeasurable economic damage in agriculture.
It is supposed that the major route for the internalization of PLGA-NPs in plant cells is the clathrin-mediated endocytosis, which starts through the formation of clathrin-coated membrane invaginations, also termed clathrin-coated pit. In this context, dynamin is a GTPase protein essential for vesicle detachment. However, in addition to the clathrin-dependent endocytosis pathway, emerging researches have revealed clathrin-independent pathways are not all dependent on dynamin in plant cells. In this study, PLGA-NPs (30 nm) loaded with the high fluorescent probe coumarin-6 (Cu6-PLGA NPs) have been synthetized by microfluidic technology. The localization of Cu6-PLGA NPs has been studied in suspended cells and roots of A. thaliana seedling by confocal microscope apparatus and by fluorescence microscopy at different times (0min, 10min, 30min, 1h, 2h and 24h in suspended cells; 0min, 10min, 30min, 80min and 5 h in roots). To investigate the mechanisms of NPs uptake and internalization, the Dynasore, a specific inhibitor of dynamin, was added to cultured cells and roots. Dynasore, whose activity is well known in animal cells, is able to block the GTPasic activity of the dynamin preventing the detachment of the vesicles from the membrane.
The obtained confocal images showed that Cu6-PLGA NPs (30 nm) at a concentration of 15 mg L-1, were rapidly internalized by A. thaliana cells, as revealed by the small highly fluorescent round bodies (endosomes) and a low diffuse background observed after 10 min from the treatment with Cu6-PLGA NPs. after 30 min from treatment, the endosomes were coalescing by appearing to be less numerous and greatest. Cu6- PLGANPs were accumulated in the cytoplasm and seemed to be stable over time: at 24 h from Cu6-PLGA NPs treatment, the fluorescence distribution pattern was similar to the one observed at 60 min. The treatment with Dynasore, at 80 μM or 160 μM for 10 minutes before the
addition of 15 mg L-1 NPs did not prevent the NPs uptake in A. thaliana suspended cells, as revealed by fluorescence visible in the cytoplasm and in spherical vesicles. The confocal analysis of in vitro roots of A. thaliana seedlings showed that 15 mg L-1 Cu6-PLGA NPs enter the root in a few minutes. In particular, Cu6-PLGA NPs penetrated through the root hairs 10 min after treatment, and the fluorescence was visible not only in the root hairs, but in almost all cells of the epidermis at longer times (30 and 80 min). Cu6-PLGA NPs stayed at the epidermis level also after 5 hours. The treatment with Dynasore at 80 or 160 μM for 30 and 60 minutes before the addition of 15 mg L-1 Cu6-PLGA NPs for 10 minutes did not prevent the uptake of NPs observed in the epidermis. Even treating the roots with a higher concentration of Dynasore (320 μM) for 30 and 60 minutes before Cu6-PLGA NPs treatment, intense fluorescence continued to be visible in the root epidermis. The cytotoxicity test with propidium iodide showed that the root cells were not viable after 120-minute treatment with Dynasore at the highest concentration (320 μM).
Our results suggested that the internalization of NPs could occur by a dynamin-independent pathway and consequently, the pathway of clathrin-independent endocytosis could be involved, in agreement with previous results obtained by using clathrin-dependent endocytosis inhibitors on grapevine cells. In addition, the PLGA-NPs were translocated from the root to the hypocotyl in the A. thaliana seedling. The results of this research add new information to the understanding of PLGA-NPs internalization pathways in plants with potential applications in the agronomic field, where NPs could be applied for purposes of sustainable agriculture.
In another study, Botrytis cinerea, and Aspergillus brasiliensis, were selected in order to investigate the uptake of nanoparticles in fungi. Botrytis cinerea is known to be the cause of grey mould disease, Aspergillus brasiliensis is a species belonging to the Nigri section. Aspergillus species are responsible for a variety of disorders in various plants and plant products, mainly as opportunistic storage molds They produce several mycotoxins cause of pulmonary aspergillosis, otomycosis and eye infections in humans. In order to study the uptake of nanoparticles in fungi, B. cinerea conidia and mycelium and A. brasiliensis conidia, mycelium and biofilm were treated with 50 nm PLGA-NPs uploaded with high fluorescent probe coumarin-6 (Cu6-PLGA NPs) and analyzed by ApoTome fluorescence microscopy. The fluorescence microscopy observations revealed that, after 10 minutes from the treatment, 50 nm Cu6-PLGA NPs penetrated rapidly B. cinerea conidia and hyphae as well as A. brasiliensis hyphae and biofilm. In an effort to investigate the antimicrobial activity of antifungals delivered by nanoparticles, pterostilbene, a naturally-derived stilbenoid or fluopyram, a synthetic antifungal, used as control, were encapsulated in PLGA-NPs and supplied at different stages of B. cinerea development. Pterostilbene and fluopyram loaded in PLGA NPs showed higher antifungal activity against B. cinerea than the free compounds. In addition, pterostilbene encapsulated in PLGA-NPs was tested for its antifungal ability against A. brasiliensis biofilm. Pterostilbene delivered by PLGA-NPs reduced A. brasililiensis biofilm formation and mature biofilm demonstrating that the PLGA-NP system can enhance the bioavailability of natural compounds in A. brasiliensis biofilm crossing the biofilm matrix barrier and delivering the molecule to fungal cells. Moreover, pterostilbene loaded in PLGA NPs was tested in an in vivo model by selecting the larvae of Galleria mellonella as a fungal in vivo model. G. mellonella was infected with A. brasiliensis conidia and treated with pterostilbene delivered by PLGA-NPs or pterostilbene supplied in free form. In vivo experiments showed an infected larvae reduction in mortality after the injection of pterostilbene loaded in PLGA-NPs compared to pterostilbene supplied in free form at the same concentration.
Based on the obtained results, PLGA NPs could represent a promising method to deliver bioactive compounds for sustainable purposes in agriculture and to enhance the effectiveness of natural and synthetic antifungals through controlled and targeted drug delivery with the aim to reduce environmental toxicity and agricultural costs
Treatment of skin and soft tissue infections due to community-associated methicillin-resistant Staphylococcus aureus in Europe: the role of trimethoprim-sulfamethoxazole0010
No full textNo abstract availabl
How could we reduce antibiotic use in critically ill patients?
No full textThe role of antibiotic pressure in the selection of antibiotic-resistant bacteria is still under debate in the scientific community and often confounded by scarce data on antibiotic usage. Several studies demonstrated that prior antibiotic exposure is likely to increase patient's colonization and infection by antimicrobial-resistant bacteria. Of even more concern is the significant mortality associated with these infections, in particular in critically ill patients. Therefore, the control of antibiotic usage in intensive care units (ICUs) is of paramount importance. Antibiotic stewardship programmes (ASP) have been demonstrated to represent a useful intervention to reduce the inappropriate antibiotic usage in hospitalized patients. A few trials were performed in ICU population with positive results. The major risk we foresee for the implementation of ASP for ICU patients is the lack of consideration of local ecology and strict quality indicators. The development of new pattern of antimicrobial resistance might be ascribed to an inappropriate ASP. European networks to define best strategies and antibiotic-care bundles need to be supported at national and international level. To optimize antibiotic use in the ICU and to fight against the spread of resistance, it is extremely important to adopt a multifaceted approach including ASP
Cognitive style modulates semantic interference effects: evidence from field dependency
Full text linkThe so-called semantic interference effect is a delay in selecting an appropriate target word in a context where semantic neighbours are strongly activated. Semantic interference effect has been described to vary from one individual to another. These differences in the susceptibility to semantic interference may be due to either differences in the ability to engage in lexical-specific selection mechanisms or to differences in the ability to engage more general, top-down inhibition mechanisms which suppress unwanted responses based on task-demands. However, semantic interference may also be modulated by an individual’s disposition to separate relevant perceptual signals from noise, such as a field-independent (FI) or a field-dependent (FD) cognitive style. We investigated the relationship between semantic interference in picture naming and in an STM probe task and both the ability to inhibit responses top-down (measured through a Stroop task) and a FI/FD cognitive style measured through the embedded figures test (EFT). We found a significant relationship between semantic interference in picture naming and cognitive style—with semantic interference increasing as a function of the degree of field dependence—but no associations with the semantic probe and the Stroop task. Our results suggest that semantic interference can be modulated by cognitive style, but not by differences in the ability to engage top-down control mechanisms, at least as measured by the Stroop task
Antimicrobial susceptibility testing of pathogens isolated from blood culture: a performance comparison of Accelerate Pheno (TM) and VITEK (R) 2 systems with the broth microdilution method
Full text linkObjectives: To compare the performance of the Accelerate PhenoTM system with that of the conventional phenotypic VITEK® 2 system for rapid antimicrobial susceptibility testing (AST) of bacterial pathogens from positive blood culture (PBC) samples, based on the reference broth microdilution (BMD) method. Methods: Prospectively collected PBCs that represented patient-unique bloodstream infection episodes were included. For PBC samples showing monomicrobial growth (n = 86), AST was performed using both Accelerate PhenoTM and VITEK® 2 systems directly from PBC broth. Colony isolates derived from subculture of PBC broth were then used for BMD testing. AST results were interpreted according to 2017 EUCAST breakpoints. Results: The overall categorical agreement between Accelerate PhenoTM system and BMD was 92.7% (467/504) for Gram-negative organisms and 99.0% (95/96) for Gram-positive organisms, with rates for very major errors of 3.6% (6/166), major errors 2.2% (9/416) and minor errors 3.8% (23/600). The overall categorical agreement between the VITEK® 2 system and BMD was 91.7% (463/505) for Gram-negative organisms and 99.0% (97/98) for Gram-positive organisms, with rates of very major errors of 2.4% (4/169), major errors 1.0% (4/416) and minor errors 5.8% (35/603). Importantly, unlike the VITEK® 2 system, no false-susceptible results occurred with two colistin-resistant organism-growing PBCs tested using the Accelerate PhenoTM system. Conclusions: Based on these findings, the Accelerate PhenoTM system can be a valid alternative for the rapid AST of Gram-negative and Gram-positive bacteria in bloodstream infections
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
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