L’expérience-mouvement : animation performative en réalité virtuelle

Cette recherche-création se situe à la frontière de l'art et du design dans le domaine de l’animation expérimentale. Elle repose sur la proposition du paradigme de l'expérience-mouvement pour l'animation de personnages et d'objets. Afin d’en démontrer la logique, il est proposé d'analyser l'outil de Motion Carving et les questions qui en sont à l’origine. Cet outil d'animation en réalité virtuelle, mis au point par l’artiste au fil de la présente recherche, donne forme à un procédé d’animation performatif et récursif répondant aux caractéristiques du paradigme de l'expérience-mouvement. La création de mouvement s’y effectue couche par couche, en manipulant des objets dans un espace immersif en temps-réel. L’outil qui émerge de cette recherche-création est performatif dans la mesure où il implique l’expérience du mouvement, par l’artiste, dans l’espace et la durée. En cela, cette approche s’oppose à l’animation frame by frame, un processus exclusivement pictural qui repose sur la création de séquences d’images représentant des poses statiques. L’argumentaire de ce mémoire retrace l’évolution de la recherche et analyse le développement de l’outil en exposant la manière dont s’est élaboré le paradigme de l’expérience-mouvement, un cadre permettant d’envisager l’animation autrement que par le procédé image par image. En accord avec une posture de praticien, la méthodologie de recherche est itérative. Les données recueillies et colligées dans un journal de recherche sont issues d’une suite de projets et documents de design visant à découvrir et expérimenter de nouvelles manières d’animer. Ce cheminement aux ramifications théoriques se transpose dans la pratique par la mise en forme du procédé d’animation Motion Carving, déjà mentionné ci-dessus. La principale contribution de ce mémoire réside donc dans la proposition d'un procédé performatif et récursif d'animation en temps réel duquel émergera non seulement une famille d'outils, mais aussi une nouvelle approche créative dans le domaine de l’animation : décomposer la structure du mouvement en couches spatiotemporelles. Cette approche a permis de réaliser différentes oeuvres artistiques en regard du paradigme de l'expérience-mouvement. Il est notamment question du projet Les trois grâces qui constitue la principale création artistique issue de la présente recherche-création

Evaluation of a Rhodomyrtus tomentosa ethanolic extract for its therapeutic potential on Staphylococcus aureus infections using in vitro and in vivo models of mastitis

International audienceAbstractAn ethanolic extract from Rhodomyrtus tomentosa leaves (RTL) was studied as a natural alternative to control Staphylococcus aureus, which is an important pathogen responsible for bovine mastitis. The minimal inhibitory concentrations (MICs) of the RTL extract and of rhodomyrtone, a pure compound isolated from the plant, were determined by a microdilution method. Rhodomyrtone and the RTL extract exhibited antibacterial activity against S. aureus, including its persistent phenotype (SCV: small-colony variant) and a biofilm hyperproducer strain, with MICs of 0.25–0.5 and 8–16 µg/mL, respectively. Time-kill kinetics showed a strong bactericidal activity for both the RTL extract- and rhodomyrtone-treated bacteria at 2 × MIC as early as 4 h post-exposure. An additive effect of the extract at 0.5 × MIC was observed in a combination with oxytetracycline or pirlimycin against S. aureus by showing a 64- to 128-fold reduction in antibiotic MICs. Moreover, the RTL extract significantly decreased the number of intracellular SCVs inside bovine mammary epithelial cells. However, the extract or its combination with pirlimycin only slightly improved the activity of pirlimycin against the bacterial colonization of mouse mammary glands. In vitro MICs determined in the presence of casein indicated that the limited activity of the RTL extract in the murine model of mastitis could be linked to neutralization of active components by milk proteins. While the RTL extract showed interesting antibacterial properties in vitro, to be considered as an alternative to antibiotics in dairy farms, formulation studies are needed to cope with the observed reduction of activity in vivo

Iron transport-mediated drug delivery using mixed-ligand siderophore-β-lactam conjugates

Abstractbackground: Assimilation of iron is essential for microbial growth. Most microbes synthesize and excrete low molecular weight iron chelators called siderophores to sequester and deliver iron by active transport processes. Specific outer membrane proteins recognize, bind and initiate transport of species-selective ferric siderophore complexes. Organisms most often have specific receptors for multiple types of siderophores, presumably to ensure adequate acquisition of the iron that is essential for their growth. Conjugation of drugs to synthetic hydroxamate or catechol siderophore components can facilitate active iron-transport-mediated drug delivery. While resistance to the siderophore—drug conjugates frequently occurs by selection of mutants deficient in the corresponding siderophore-selective outer membrane receptor, the mutants are less able to survive under iron-deficient conditions and in vivo. We anticipated that synthesis of mixed ligand siderophore—drug conjugates would allow active drug delivery by multiple iron receptor recognition and transport processes, further reducing the likelihood that resistant mutants would be viable.Results: Mixed ligand siderophore-drug conjugates were synthesized by combining hydroxamate and catechol components in a single compound that could chelate iron, and that also contained a covalent linkage to carbacephalosporins, as representative drugs. The new conjugates appear to be assimilated by multiple active iron-transport processes both in wild type microbes and in selected mutants that are deficient in some outer membrane iron-transport receptors.Conclusions: The concept of active iron-transport-mediated drug delivery can now be extended to drug conjugates that can enter the cell through multiple outer membrane receptors. Mutants that are resistant to such conjugates should be severely impaired in iron uptake, and therefore particularly prone to iron starvation

Staphylococcus aureus sigma B-dependent emergence of small-colony variants and biofilm production following exposure to Pseudomonas aeruginosa 4-hydroxy-2-heptylquinoline-N-oxide

<p>Abstract</p> <p>Background</p> <p><it>Staphylococcus aureus </it>and <it>Pseudomonas aeruginosa </it>are often found together in the airways of cystic fibrosis (CF) patients. It was previously shown that the <it>P. aeruginosa </it>exoproduct 4-hydroxy-2-heptylquinoline-<it>N-</it>oxide (HQNO) suppresses the growth of <it>S. aureus </it>and provokes the emergence of small-colony variants (SCVs). The presence of <it>S. aureus </it>SCVs as well as biofilms have both been associated with chronic infections in CF.</p> <p>Results</p> <p>We demonstrated that HQNO stimulates <it>S. aureus </it>to form a biofilm in association with the formation of SCVs. The emergence of SCVs and biofilm production under HQNO exposure was shown to be dependent on the activity of the stress- and colonization-related alternative sigma factor B (SigB). Analysis of gene expression revealed that exposure of a prototypical <it>S. aureus </it>strain to HQNO activates SigB, which was leading to an increase in the expression of the fibronectin-binding protein A and the biofilm-associated <it>sarA </it>genes. Conversely, the quorum sensing accessory gene regulator (<it>agr</it>) system and the α-hemolysin gene were repressed by HQNO. Experiments using culture supernatants from <it>P. aeruginosa </it>PAO1 and a double chamber co-culture model confirmed that <it>P. aeruginosa </it>stimulates biofilm formation and activates SigB in a <it>S. aureus </it>strain isolated from a CF patient. Furthermore, the supernatant from <it>P. aeruginosa </it>mutants unable to produce HQNO induced the production of biofilms by <it>S. aureus </it>to a lesser extent than the wild-type strain only in a <it>S. aureus </it>SigB-functional background.</p> <p>Conclusions</p> <p>These results suggest that <it>S. aureus </it>responds to HQNO from <it>P. aeruginosa </it>by forming SCVs and biofilms through SigB activation, a phenomenon that may contribute to the establishment of chronic infections in CF patients.</p

Mulifractal phase transitions: the origin of self-organized criticality in earthquakes

International audienceFractal and occasionally multifractal behaviour has been invoked to characterize (independently of their magnitude) the spatial distribution of seismic epicenters, whereas more recently, the frequency distribution of magnitudes (irrespective of their spatial location) has been considered as a manifestation of Self-Organized Criticality (SOC). In this paper we relate these two aspects on rather general grounds, (i.e. in a model independent way), and further show that this involves a non-classical SOC. We consider the multifractal characteristics of the projection of the space-time seismic process onto the horizontal plane whose values are defined by the measured ground displacements, we show that it satisfies the requirements for a first order multifractal phase transition and by implication for a non-classical SOC. We emphasize the important consequences of the stochastic alternative to the classical (deterministic) SOC

In Vivo Bactericidal Efficacy of GWH1 Antimicrobial Peptide Displayed on Protein Nanoparticles, a Potential Alternative to Antibiotics

Oligomerization of antimicrobial peptides into nanosized supramolecular complexes produced in biological systems (inclusion bodies and self-assembling nanoparticles) seems an appealing alternative to conventional antibiotics. In this work, the antimicrobial peptide, GWH1, was N-terminally fused to two different scaffold proteins, namely, GFP and IFN-γ for its bacterial production in the form of such recombinant protein complexes. Protein self-assembling as regular soluble protein nanoparticles was achieved in the case of GWH1-GFP, while oligomerization into bacterial inclusion bodies was reached in both constructions. Among all these types of therapeutic proteins, protein nanoparticles of GWH1-GFP showed the highest bactericidal effect in an in vitro assay against Escherichia coli, whereas non-oligomerized GWH1-GFP and GWH1-IFN-γ only displayed a moderate bactericidal activity. These results indicate that the biological activity of GWH1 is specifically enhanced in the form of regular multi-display configurations. Those in vitro observations were fully validated against a bacterial infection using a mouse mastitis model, in which the GWH1-GFP soluble nanoparticles were able to effectively reduce bacterial loads

Novel Riboswitch Ligand Analogs as Selective Inhibitors of Guanine-Related Metabolic Pathways

Riboswitches are regulatory elements modulating gene expression in response to specific metabolite binding. It has been recently reported that riboswitch agonists may exhibit antimicrobial properties by binding to the riboswitch domain. Guanine riboswitches are involved in the regulation of transport and biosynthesis of purine metabolites, which are critical for the nucleotides cellular pool. Upon guanine binding, these riboswitches stabilize a 5′-untranslated mRNA structure that causes transcription attenuation of the downstream open reading frame. In principle, any agonistic compound targeting a guanine riboswitch could cause gene repression even when the cell is starved for guanine. Antibiotics binding to riboswitches provide novel antimicrobial compounds that can be rationally designed from riboswitch crystal structures. Using this, we have identified a pyrimidine compound (PC1) binding guanine riboswitches that shows bactericidal activity against a subgroup of bacterial species including well-known nosocomial pathogens. This selective bacterial killing is only achieved when guaA, a gene coding for a GMP synthetase, is under the control of the riboswitch. Among the bacterial strains tested, several clinical strains exhibiting multiple drug resistance were inhibited suggesting that PC1 targets a different metabolic pathway. As a proof of principle, we have used a mouse model to show a direct correlation between the administration of PC1 and the reduction of Staphylococcus aureus infection in mammary glands. This work establishes the possibility of using existing structural knowledge to design novel guanine riboswitch-targeting antibiotics as powerful and selective antimicrobial compounds. Particularly, the finding of this new guanine riboswitch target is crucial as community-acquired bacterial infections have recently started to emerge

Plant Antimicrobial Agents and Their Effects on Plant and Human Pathogens

To protect themselves, plants accumulate an armoury of antimicrobial secondary metabolites. Some metabolites represent constitutive chemical barriers to microbial attack (phytoanticipins) and others inducible antimicrobials (phytoalexins). They are extensively studied as promising plant and human disease-controlling agents. This review discusses the bioactivity of several phytoalexins and phytoanticipins defending plants against fungal and bacterial aggressors and those with antibacterial activities against pathogens affecting humans such as Pseudomonas aeruginosa and Staphylococcus aureus involved in respiratory infections of cystic fibrosis patients. The utility of plant products as “antibiotic potentiators” and “virulence attenuators” is also described as well as some biotechnological applications in phytoprotection