Daptomycin resistance mechanisms in clinically derived Staphylococcus aureus strains assessed by a combined transcriptomics and proteomics approach

Objectives The development of daptomycin resistance in Staphylococcus aureus is associated with clinical treatment failures. The mechanism(s) of such resistance have not been clearly defined. Methods We studied an isogenic daptomycin-susceptible (DAPS) and daptomycin-resistant (DAPR) S. aureus strain pair (616; 701) from a patient with relapsing endocarditis during daptomycin treatment, using comparative transcriptomic and proteomic techniques. Results Minor differences in the genome content were found between strains by DNA hybridization. Transcriptomic analyses identified a number of genes differentially expressed in important functional categories: cell division; metabolism of bacterial envelopes; and global regulation. Of note, the DAPR isolate exhibited reduced expression of the major cell wall autolysis gene coincident with the up-regulation of genes involved in cell wall teichoic acid production. Using quantitative (q)RT-PCR on the gene cadre putatively involved in cationic peptide resistance, we formulated a putative regulatory network compatible with microarray data sets, mainly implicating bacterial envelopes. Of interest, qRT-PCR of this same gene cadre from two distinct isogenic DAPS/DAPR clinical strain pairs revealed evidence of other strain-dependent networks operative in the DAPR phenotype. Comparative proteomics of 616 versus 701 revealed a differential abundance of proteins in various functional categories, including cell wall-associated targets and biofilm formation proteins. Phenotypically, strains 616 and 701 showed major differences in their ability to develop bacterial biofilms in the presence of the antibacterial lipid, oleic acid. Conclusions Compatible with previous in vitro observations, in vivo-acquired DAPR in S. aureus is a complex, multistep phenomenon involving: (i) strain-dependent phenotypes; (ii) transcriptome adaptation; and (iii) modification of the lipid and protein contents of cellular envelope

Identification and functional expression of the mitochondrial pyruvate carrier

Les mitochondries sont des organites cellulaires entourés de deux membranes présents chez presque tous les eucaryotes. Les mitochondries sont essentielles pour de nombreux processus cellulaires tels que la production d'énergie, la synthèse des centres fer-soufre, le métabolisme de certains acides aminés et la mort cellulaire. Les mitochondries contiennent leur propre génome qui code pour treize protéines de la chaine respiratoire. Cependant, plus de mille protéines sont présentes dans la mitochondrie et sont donc encodées par le génome nucléaire, traduites dans le cytoplasme et importées par une machinerie spécialisée à travers les membranes mitochondriales externes et internes. Les mitochondries importent non seulement des protéines mais également des molécules impliquées dans les différents processus qui se déroulent dans ces organites. En particulier, le pyruvate, produit dans le cytoplasme par la glycolyse, est importé dans la mitochondrie pour y être oxydé. La glycolyse est un processus rapide qui présente un rendement faible puisque seulement 2 molécules d'ATP sont produites par molécule de glucose. Lorsque le pyruvate entre dans la mitochondrie, il est transformé en acetyl-CoA et entre ensuite dans le cycle de Krebs où des équivalents réducteurs sont produits et utilisés par la chaine respiratoire pour produire de l'énergie par phosphorylation oxydative. Ceci permet à la mitochondrie, grâce à la consommation d'oxygène, de produire 34 molécules d'ATP par molécule de glucose. Le transport du pyruvate dans la mitochondrie est effectué par un transporteur dont les caractéristiques biochimiques ont été décrites en 1975. Jusqu'à aujourd'hui, et malgré de nombreuses recherches, les protéines qui le composent étaient inconnues

Mitochondrial dynamics and cancer

Mitochondrial morphology is regulated by continuous fusion and fission events that are essential for maintaining a normal mitochondrial function. If the last years have witnessed major discoveries in the characterization of the fission and fusion machineries, little is known about the physiological role of mitochondrial dynamics. In this review we report the results showing evidences of relationships between mitochondrial dynamics and cellular metabolism, autophagy or apoptosis. We discuss how different mitochondrial alterations observed in cancer cells could be linked to unbalanced mitochondrial fission or fusion events and how this could impinge on key essential cellular processes, thereby contributing to tumorigenesis

Adaptations des recommandations pour la pratique clinique: l'exemple du Programme cantonal Diabète de Vaud [Adaptation of clinical practice guidelines--the example of cantonal Diabetes Program].

With the growing number of scientific publications, practitioners can use scientific knowledge synthesis, including Clinical Practice Guidelines (CPG). The practical use of a CPG implies considering the context, that is the local healthcare system and the patient. Thus, the CPG can never replace the expertise of the practitioner! Diabetes is a wide public health issue and the canton of Vaud established the cantonal Diabetes Program (cDP), to optimize the care of diabetic patients. The cDP has many projects including the adaptation of reliable CPG to local needs. We present the pros and cons of the CPG in the cDP and the methods to adapt it to the regional healthcare context, and also at an individual level

Membrane Remodeling Induced By The Dynamin-Related Protein Drp1 Stimulates Bax Oligomerization

In response to many apoptotic stimuli, oligomerization of Bax is essential for mitochondrial outer membrane permeabilization and the ensuing release of cytochrome c. These events are accompanied by mitochondrial fission that appears to require Drp1, a large GTPase of the dynamin superfamily. Loss of Drp1 leads to decreased cytochrome c release by a mechanism that is poorly understood. Here we show that Drp1 stimulates tBid-induced Bax oligomerization and cytochrome c release by promoting tethering and hemifusion of membranes in vitro. This function of Drp1 is independent of its GTPase activity and relies on arginine 247 and the presence of cardiolipin in membranes. In cells, overexpression of Drp1 R247A/E delays Bax oligomerization and cell death. Our findings uncover a function of Drp1 and provide insight into the mechanism of Bax oligomerization. © 2010 Elsevier Inc

Light Emitting Si‐Based Mie Resonators: Toward a Huygens Source of Quantum Emitters

International audienceSilicon-based micro- and nano-structures for light management at near-infrared and visible frequencies have been widely exploited for guided optics and metasurfaces. However, light emission with this material has been hampered by the indirect character of its bandgap. Here it is shown that, via ion beam implantation, light emitting G-centers can be directly embedded within Si-based Mie resonators previously obtained by solid state dewetting. Size- and position-dependent, directional light emission at 120 K is demonstrated experimentally and confirmed by finite difference time domain simulations. It is estimated that, with an optimal coupling of the G-centers emission with the resonant antennas, a collection efficiency of about 90% can be reached using a conventional objective lens. The integration of these telecom-frequency emitters in resonant antennas is relevant for their efficient exploitation in quantum optics applications and more generally to Si-based photonic metasurfaces

Directional emission of point defects in silicon emitting in telecom wavelength through the use of Mie resonators

National audienc