Elaboration de céramiques nanostructurées en carbure de silicium (de la synthèse de la poudre à la céramique frittée)

Les matériaux des réacteurs nucléaires du futur seront soumis à des températures et des flux de neutrons très élevés. Il est alors envisagé d utiliser des matériaux céramiques tels que le carbure de silicium sous la forme de composite SiCf/SiC nanostructuré. Il est cependant encore nécessaire de vérifier l apport de la nanostructuration sur le comportement de ce matériau sous irradiations. Afin de vérifier la faisabilité et déterminer les propriétés de la matrice, il a été envisagé de fabriquer celle-ci seule par métallurgie des poudres à partir de nanoparticules de SiC. L objectif est d obtenir du SiC dense et nanostructuré sans avoir recours à des ajouts de frittage. Pour cela, une étude paramétrique de la phase de synthèse et de densification a été réalisée dans l objectif de mieux connaître l influence des paramètres clés et les mécanismes mis en jeu. Ainsi l étude de la synthèse des nanopoudres par pyrolyse laser a permis de produire, avec des taux de production élevés, des lots de nanoparticules de SiC homogènes dont la taille peut être ajustée entre 15 et 90 nm. Ces poudres ont été densifiées par une méthode innovante : le Spark Plasma Sintering (SPS). L étude puis l optimisation des paramètres clés ont permis de densifier, sans avoir recours à des ajouts, du SiC (3.1 g/cm3) tout en conservant la nanostructuration du matériau. Les matériaux obtenus ont été caractérisés thermiquement et mécaniquement afin de déterminer l influence de la nanostructuration sur leur comportement.The materials used inside future nuclear reactors will be subjected to very high temperature and neutron flux. Silicon carbide, in the form of SiCf/SiC nanostructured composite is potentially interesting for this type of application. It is again necessary to verify the contribution of nanostructure on the behaviour of this material under irradiation. To verify the feasibility and determine the properties of the matrix, it was envisaged to produce it alone by powder metallurgy from SiC nanoparticles. The objective is to obtain nanostructured SiC ceramic fully densified and without using sintering aids. For that, a parametric study of the phase of synthesis and agglomeration was carried out, with for objective the determining the active mechanisms and the influence of the key parameters. Thus, the study of the nanopowder synthesis by laser pyrolysis made it possible to produce, with high production rates, homogeneous batches of SiC nanoparticles whose size can be adjusted between 15 and 90 nm. These powders were densified by an innovating method: Spark Plasma Sintering (SPS). The study and the optimization of the key parameters allowed the densification of silicon carbide ceramic without sintering aids while preserving the nanostructure of material. The thermal and mechanical properties of final materials were studied in order to determine the influence of microstructure on their properties.ORSAY-PARIS 11-BU Sciences (914712101) / SudocSudocFranceF

Overly broad-spectrum antibiotic treatment of wild-type <i>Pseudomonas aeruginosa</i> infections in relation to the EUCAST new definition of susceptibility testing categories, a retrospective multicentre cohort study

Objectives: EUCAST changed the definition of the 'intermediate' (I) category in 2019, now defined as 'susceptible, increased exposure'. This new definition could lead to an increased prescription of antibiotics still reported as 'S', compared with those now reported as 'I'. The objective of this study was to evaluate the influence of this definition on the use of overly broad-spectrum antibiotics for the treatment of infections caused by WT Pseudomonas aeruginosa. Methods: A retrospective observational multicentre study was conducted, involving five hospitals. Two 15 month study periods were defined, before and after the implementation of the new definition. All patients with an infection caused by WT P. aeruginosa treated by β-lactams were included. The main endpoint was the proportion of patients treated by an overly broad-spectrum antibiotic treatment by meropenem or ceftolozane/tazobactam. Results: Two hundred and ninety-one patients were included. No difference between groups was found, in terms of infection, microbiology or demographic characteristics. Two overly broad-spectrum antibiotic treatments by meropenem or ceftolozane/tazobactam were observed in Period 1 (1.2%), versus 13 in Period 2 (10.8%; P < 0.001). No overly broad-spectrum treatment was observed when the antimicrobial stewardship team had given advice. Conclusions: This new definition can cause a negative impact on the use of overly broad-spectrum antibiotic treatment due to misunderstanding by clinicians. Its successful implementation requires adaptation of software for reporting antibiotic susceptibility, a sustained strong information campaign by microbiologists and support by an antimicrobial stewardship team

Blood Cultures for the Diagnosis of Infective Endocarditis: What Is the Benefit of Prolonged Incubation?

To assess the need for prolonged incubation of blood culture bottles beyond five days for the diagnosis of infectious endocarditis (IE), we conducted a retrospective cohort study of 6109 sets of two blood culture bottles involving 1211 patients admitted to the Henri Mondor University Hospital for suspicion of IE between 1 January 2016 and 31 December 2019. Among the 322 patients with IE, 194 had positive blood cultures in our centre. Only one patient with a time-to-positivity blood culture of more than 120 h (5 days) was found. The main cause for the 22 patients with positive blood cultures after five days was contamination with Cutibacterium acnes. Our results do not support extending the duration of incubation of blood culture bottles beyond five days for the diagnosis of infectious endocarditis, with the exception of patients with risk factors for C. acnes infection

Pax7-expressing satellite cells are indispensable for adult skeletal muscle regeneration

International audienceDistinct cell populations with regenerative capacity have been reported to contribute to myofibres after skeletal muscle injury, including non-satellite cells as well as myogenic satellite cells. However, the relative contribution of these distinct cell types to skeletal muscle repair and homeostasis and the identity of adult muscle stem cells remain unknown. We generated a model for the conditional depletion of satellite cells by expressing a human diphtheria toxin receptor under control of the murine Pax7 locus. Intramuscular injection of diphtheria toxin during muscle homeostasis, or combined with muscle injury caused by myotoxins or exercise, led to a marked loss of muscle tissue and failure to regenerate skeletal muscle. Moreover, the muscle tissue became infiltrated by inflammatory cells and adipocytes. This localised loss of satellite cells was not compensated for endogenously by other cell types, but muscle regeneration was rescued after transplantation of adult Pax7(+) satellite cells alone. These findings indicate that other cell types with regenerative potential depend on the presence of the satellite cell population, and these observations have important implications for myopathic conditions and stem cell-based therapeutic approaches

Psoas abscess and chronic Q fever: a contiguous or hematogenous complication? A case report and literature review

<p>Few cases of psoas abscesses (PA) during chronic Q fever have been reported, and the route of transmission remains unknown. Here, we report a new case and have performed a systematic literature review to determinate the spreading route of this complication. Medline, EMBASE and Web of Science were searched. Local spreading was supported by endocarditis exclusion, evidence of vascular infection and absence of distantly infected sites. Among 275 retrieved references, 179 were initially rejected, and 85 additional references were rejected after full-text review. A total of 11 studies, reporting 13 cases, were included. Additionally, we reported one new case. A total of 14/14 cases reached Q fever vascular infection diagnostic criteria, and 7/14 provided adequate evidence supporting a causal relationship between Q fever vascular infection and PA. All patients presented aorta defects. In conclusion, Q fever PA results from the spreading of a local infection and occurs specifically in patients presenting a vascular graft or an abdominal aortic aneurysm.</p

Incidence of infectious morbidity events after second-line antiretroviral therapy initiation in HIV-infected adults in Yaoundé, Cameroon

International audienceBACKGROUND:Since antiretroviral therapy (ART), HIV-infected individuals experience mainly non-AIDS-related conditions, among which infectious events are prominent. We aimed to estimate incidence and describe overall spectrum of infectious events, including all grade events, among HIV-1-infected adults failing first-line ART in Yaoundé, Cameroon.METHODS:All patients from Cameroon enrolled in the second-line ART 2LADY trial (ANRS12169) were included in this secondary analysis. Medical files were reviewed with predefined criteria for diagnosis assessment. Incidence rates (IR) were estimated per 100 person-years (% PY).RESULTS:A total of 302 adult patients contributing 840 PY experienced 596 infectious events (IR 71% PY). Only 29 (5%) events were graded as severe. Most frequent infections were upper respiratory tract infections (15% PY), diarrhoea (9% PY) and malaria (9% PY). A total of 369 (62%) infections occurred during the first year (IR 130% PY) followed by a persistent lower incidence during the following 3 years. Higher IR were observed in patients with CD4+ T-cell count <200 cells/mm3 for all infectious events except for mycobacterial and parasitic infections. IR of viral, bacterial and parasitic infectious events were lower in case of co-trimoxazole use in patients with CD4+ T-cell count <200 cells/mm3.CONCLUSIONS:Infectious events are common and mainly occur during the first year after treatment initiation. Second-line ART initiation had a positive impact on the entire spectrum of infectious morbidity

BRCA1/BRCA2 germline mutations and chemotherapy-related hematological toxicity in breast cancer patients

BRCA1 and BRCA2 proteins are central to DNA repair process through homologous recombination. We hypothesize that BRCA1/BRCA2 mutation carriers may exhibit increased hematological toxicity when receiving genotoxic chemotherapy

Clinical outcome of breast cancer in carriers of BRCA1 and BRCA2 mutations according to molecular subtypes

BRCA1/BRCA2 genes play a central role in DNA repair and their mutations increase sensitivity to DNA-damaging agents. There are conflicting data regarding the prognostic value of BRCA germline mutations in breast cancer (BC) patients. We collected clinical, pathological and genetic data of a cohort 925 BC patients preselected for genetic screening and treated with neoadjuvant or adjuvant chemotherapy, of whom 266 were BRCA carriers. Overall, 171 women carried a BRCA1 mutation, 95 carried a BRCA2 mutation, and 659 were non-carriers. In the entire cohort, there was a prolonged disease-free survival (DFS) for BRCA carriers (hazard ratio (HR) = 0.63; 95% confidence interval (CI), 0.44-0.90 for BRCA1; HR = 0.72; 95%CI, 0.47-1.1 for BRCA2; p = 0.020) and a trend toward prolonged disease-specific survival (DSS; HR = 0.65; 95%CI, 0.40-1.1 for BRCA1; HR = 0.78; 95%CI, 0.44-1.38 for BRCA2; p = 0.19) though not statistically significant. In the TNBC group, BRCA carriers had prolonged DFS (adjusted HR = 0.50; 95%CI, 0.28-0.89 for BRCA1; adjusted HR = 0.37; 95%CI, 0.11-1.25, for BRCA2; p = 0.034) and DSS (adjusted HR = 0.42; 95%CI, 0.21-0.82 for BRCA1; adjusted HR = 0.45; 95%CI, 0.11-1.9 for BRCA2; p = 0.023). In the non-TNBC group, the BRCA1 or BRCA2 mutations did not have any impact on survival. These results suggest that BRCA1/BRCA2 germline mutations are associated with prolonged survival only if women were diagnosed with TNBC

Vasoplegic Syndrome after Cardiac Surgery for Infective Endocarditis

Purpose: Post-operative vasoplegic syndrome is a dreaded complication in infective endocarditis (IE). Methods and Results: This retrospective study included 166 consecutive patients referred to cardiac surgery for non-shocked IE. Post-operative vasoplegic syndrome was defined as a persistent hypotension (mean blood pressure n = 8) of vasoplegic patients had a post-operative documented infection (6 positive blood cultures) and no difference was reported between vasoplegic and non-vasoplegic patients for valve culture and the timing of cardiac surgery. Of the 23 (13.8%) in hospital-deaths, 87.0% (n = 20) occurred in the vasoplegic group and the main causes of death were multiorgan failure (n = 17) and neurological complications (n = 3). Variables independently associated with vasoplegic syndrome were CPB duration (1.82 (1.16–2.88) per tertile) and NTproBNP level (2.11 (1.35–3.30) per tertile). Conclusions: Post-operative vasoplegic syndrome is frequent and is the main cause of death after IE cardiac surgery. Our data suggested that the mechanism of vasoplegic syndrome was more related to inflammatory cardiovascular injury rather than the consequence of ongoing bacteremia