Antibacterial Properties of Polyphenols: Characterization and QSAR (Quantitative Structure–Activity Relationship) Models

Besides their established antioxidant activity, many phenolic compounds may exhibit significant antibacterial activity. Here, the effect of a large dataset of 35 polyphenols on the growth of 6 foodborne pathogenic or food-spoiling bacterial strains, three Gram-positive ones (Staphylococcus aureus, Bacillus subtilis, and Listeria monocytogenes) and three Gram-negative ones (Escherichia coli, Pseudomonas aeruginosa, and Salmonella Enteritidis), have been characterized. As expected, the effects of phenolic compounds were highly heterogeneous ranging from bacterial growth stimulation to antibacterial activity and depended on bacterial strains. The effect on bacterial growth of each of the polyphenols was expressed as relative Bacterial Load Difference (BLD) between a culture with and without (control) polyphenols at a 1 g L−1 concentration after 24 h incubation at 37°C. Reliable Quantitative Structure-Activity Relationship (QSAR) models were developed (regardless of polyphenol class or the mechanism of action involved) to predict BLD for E. coli, S. Enteritidis, S. aureus, and B. subtilis, unlike for L. monocytogenes and P. aeruginosa. L. monocytogenes was generally sensitive to polyphenols whereas P. aeruginosa was not. No satisfactory models predicting the BLD of P. aeruginosa and L. monocytogenes were obtained due to their specific and quite constant behavior toward polyphenols. The main descriptors involved in reliable QSAR models were the lipophilicity and the electronic and charge properties of the polyphenols. The models developed for the two Gram-negative bacteria (E. coli, S. Enteritidis) were comparable suggesting similar mechanisms of toxic action. This was not clearly observed for the two Gram-positive bacteria (S. aureus and B. subtilis). Interestingly, a preliminary evaluation by Microbial Adhesion To Solvents (MATS) measurements of surface properties of the two Gram-negative bacteria for which QSAR models were based on similar physico-chemical descriptors, revealed that MATS results were also quite similar. Moreover, the MATS results of the two Gram-positive bacterial strains S. aureus and B. subtilis for which QSARs were not based on similar physico-chemical descriptors also strongly differed. These observations suggest that the antibacterial activity of most of polyphenols likely depends on interactions between polyphenols and bacterial cells surface, although the surface properties of the bacterial strains should be further investigated with other techniques than MATS

Effect of interactions of plant phenolics with bovine meat proteins on their antibacterial activity

The activity of 5 phenolics totally inhibiting the growth of Staphylococcus aureus CNRZ3 at a 1 g L−1 concentration in Mueller-Hinton broth for 24 h incubation at 37 °C was reevaluated at 37 °C for 24 h, 15 °C for 6 days, or 6 °C for 8 days in the presence of up to 20% (w/w) bovine meat proteins to mimic the temperature of refrigerated storage of bovine meat and its protein content, respectively. These changes affected in a different way the antibacterial activity of the 5 phenolics. Isobutyl-4-hydroxybenzoate kept its bactericidal activity, while naphthazarin was bactericidal at 6 °C and 15 °C but not at 37 °C in the presence of bovine meat proteins. Gallocyanin was bactericidal at 37 °C up to a 5% (w/w) protein content in the medium but not at 15 °C or 6 °C. Resveratrol and chrysin always lost their bacteriostatic activity when bovine meat proteins were added. The partition coefficient at 6 °C of each phenolic between a 20% (w/w) bovine meat extract suspension with and without proteins was determined. The antibacterial activity reduction of phenolics in the presence of bovine meat proteins was correlated with their affinity for bovine meat protein

De la mesure au traitement de l’information: les apports de la chimiométrie à la métrologie des sciences analytiques

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Caractérisation optique de milieux dispersés concentrés sous écoulement

De nombreux procédés d'élaboration, de traitement et de mise en forme de solides et de particules, ou plus généralement de formulation, mettent en oeuvre des milieux complexes dispersés concentrés. Ces procédés sont le siège de phénomènes de rupture, de coalescence ou d'agrégation des particules. La difficulté de compréhension et donc de modélisation de ces phénomènes est liée à la difficulté de mise au point de méthodes d'analyse in situ ou en ligne des procédés. L'objectif de cette étude est d'évaluer les potentialités d'un capteur basé sur le principe de la diffusion multiple de la lumière et développé par la société Formulaction, pour caractériser les milieux denses dispersés sous écoulement. La méthode optique utilisée, non-intrusive, permet la mesure des flux rétrodiffusés et transmis par le système à analyser. Des modèles physiques sont utilisés pour obtenir, à partir des mesures optiques, les propriétés physiques du milieu dispersé (diamètre moyen et fraction volumique des particules). Un dispositif expérimental rhéo-optique, combinant la technique optique et un système Couette, a été mis au point et permet la caractérisation des milieux dispersés concentrés sous écoulement contrôlé. Des expériences réalisées dans ce dispositif et effectuées sur des suspensions "modèle" de latex stabilisées, ont permis de dégager les effets du cisaillement sur la variation de signaux optiques, en relation avec les modifications de la microstructure des suspensions sous écoulement et les phénomènes de diffusion dépendante. Le dispositif rhéo-optique a par ailleurs permis de suivre in situ et temps réel les cinétiques de floculation par déplétion de polymère dans ces suspensions concentrées de latex en écoulement. Des mesures rhéologiques complémentaires ont permis de valider les interprétations issues des analyses rhéo-optiques. Finalement, la méthode optique a été appliquée au contrôle en ligne de la précipitation ou du broyage en voie humide de suspensions concentrées de carbonate de calcium et au suivi de la déstabilisation d'une émulsion commerciale sous écoulement.TOULOUSE-ENSIACET (315552325) / SudocSudocFranceF

Using Local Knowledge Graph Construction to Scale Seq2Seq Models to Multi-Document Inputs

International audienceQuery-based open-domain NLP tasks require information synthesis from long and diverse web results. Current approaches extrac-tively select portions of web text as input to Sequence-to-Sequence models using methods such as TF-IDF ranking. We propose constructing a local graph structured knowledge base for each query, which compresses the web search information and reduces redundancy. We show that by linearizing the graph into a structured input sequence, models can encode the graph representations within a standard Sequence-to-Sequence setting. For two generative tasks with very long text input , long-form question answering and multi-document summarization, feeding graph representations as input can achieve better performance than using retrieved text portions

Augmenting Transformers with KNN-Based Composite Memory for Dialog

International audienceVarious machine learning tasks can benefit from access to external information of different modalities, such as text and images. Recent work has focused on learning architectures with large memories capable of storing this knowledge. We propose augmenting generative Transformer neural networks with KNN-based Information Fetching (KIF) modules. Each KIF module learns a read operation to access fixed external knowledge. We apply these modules to generative dialog modeling, a challenging task where information must be flexibly retrieved and incorporated to maintain the topic and flow of conversation. We demonstrate the effectiveness of our approach by identifying relevant knowledge required for knowledgeable but engaging dialog from Wikipedia, images, and human-written dialog utterances, and show that leveraging this retrieved information improves model performance, measured by automatic and human evaluation

Les voisinages de l’UE sont-ils les périphéries de l’UE ?La régionalisation économique : l’intégration par le commerce.

Cet article propose d’étudier la nature des relations centre/périphérie établies entre l’Union européenne et les pays de son immédiat voisinage, en mobilisant plusieurs indicateurs (échanges commerciaux, investissements directs, aides publiques au développement, migrations et remises d’épargne). Les relations avec les pays proches restent très dissymétriques. Mais l’Union n’est plus seulement un acteur économique et commercial. On constate que son influence est croissante en tant qu’acteur politique, en particulier à travers la mise en oeuvre de la politique de voisinage. Cette situation nouvelle remet en cause le traditionnel modèle centre/ périphérie appliqué à l’Union européenne et aux pays proches, car la géographie qu’il dessine est fondée sur des critères exclusivement économiques. Si l’on remplace les critères économiques par des critères politiques, le statut des pays proches vis-à-vis de l’Union européenne n’est plus le même. Si l’UE apparaît comme un centre économique puissant et peu contesté dans son environnement régional, elle s’érige peu à peu en centre politique émergent. Néanmoins, elle est encore un centre incomplet car contesté et concurrencé par certains pays proches.This paper analyses the relevance of the centre/periphery model applied to the relations between the European Union and the all the surrounding countries (i. e. Neighbour Countries, Russia and Western Balkans). The description of these relations is based on several indicators such as trade exchanges, foreign direct investments, official development aid, international migrations and remittances. It appears that the relations between EU and those countries remain strongly dissymmetric. But, it also appears that EU is no more only an economic and commercial centre. Its influence as a political actor has been growing since the 1990. This is particularly obvious in the case since the enforcement of the neighbourhood policy and in the political commitment of EU in the Western Balkans. This situation allows every observer of EU external relations to reconsider the traditional centre/periphery model. This model is strictly based on economic factors. This is no longer sufficient and it is no more relevant to give an interpretation of the current relations between EU and the closest countries. It is then necessary to take political factors more into consideration, along with economic ones. Then, the traditional geographical representation of EU as a dominant centre surrounded by dominated peripheries gets is less clear. On the political point of view, EU has a dominant influence only in certain regions and countries, especially on the candidate ones. In the other countries, its status as a political centre is contested and eventually denied. The paper ends with a short analyse of the newly reformed European Neighbourhood Policy. Apparently, this reform will not be sufficient to enhance the political influence of EU in all the countries of its neighbourhood

Dissolution kinetics of zinc oxide and its relationship with physicochemical characteristics

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