Introduction

Peu de concepts se révèlent aussi polysémiques que ceux d’environnement et de santé. Quand de plus ils se voient associés, le résultat peut conduire à une multiplicité de sens possibles. Environnement et santé comme apposition de deux champs qui s’expliqueraient mutuellement, environnement ET santé où l’accent est placé sur les interrelations et les liens qui s’inscrivent dans un fonctionnement systémique, santé-environnement comme un raccourci de l’expression précédente servant de cadre à de..

La dynamique spatio-temporelle du virus Ebola dans l’espace CEDEAO

L’espace CEDEAO subit de profondes mutations spatiales liées à une forte croissance démographique, au changement climatique et à une croissance économique exceptionnelle. Entre 1950 et 2015, cet espace a accueilli 280 millions nouveaux habitants, soit une moyenne de 4,3 millions nouveaux arrivants par an, parmi lesquels 2,4 millions nouveaux urbains et 1,9 millions nouveaux ruraux. Les dynamiques de peuplements impulsées par ces forces démographiques, climatiques et économiques, s’effectuent parfois en direction des terres neuves parmi lesquelles les espaces protégés. Ces derniers constituent des réserves de biodiversité qui hébergent des réservoirs de pathogènes et d’insectes vecteurs. L’homme, en exploitant ces nouveaux territoires, s’exposent donc à la piqûre d’insectes vecteurs de maladies ou au contact d’animaux réservoirs de pathogènes, tel que le virus Ebola. Par la densification de sa présence et son extension spatiale généralisée, l’homme créé également de plus en plus de promiscuité avec les animaux sauvages. Dans l’espace CEDEAO, les chimpanzés et quelques espèces de chauve-souris semblent représenter le plus grand danger pour l’homme au regard du risque de transmission du virus Ebola. Cette étude replace l’épidémie d’Ebola survenue en 2013 en Guinée dans son contexte historique et panafricain. Puis, elle présente brièvement le rôle connu de la faune sauvage dans l’épidémiologie d’Ebola et de quelles manières les changements environnementaux opèrent sur les principaux réservoirs connus de ce virus. Ensuite, elle retrace les grandes lignes de l’évolution spatio-temporelle de l’épidémie d’Ebola survenue dans l’espace CEDEAO, en tentant de faire apparaître les tenants et les aboutissants géographiques de cette catastrophe épidémiologique.ECOWAS space undergoes deep modifications related to population growth, climate change and economic development. Between 1950 and 2015, this space accommodated 280 million new inhabitants, i.e. an average of 4.3 million new arrivals a year, among which 2.4 million new urban and 1.9 million new rural. The dynamics of settlements caused by these demographic, climatic and economic phenomena are most of the time carried out towards free lands, among which protected areas. The latter constitutes reserves of biodiversity but also a reservoir of pathogens and of insect vectors. Man, by exploiting these new territories, thus expose himself to the bite of an insect vectors of disease or to a contact with an animal reservoir of a pathogen, such as the Ebola virus. By the thickening of its presence and its generalized space extension, man also created more and more promiscuity with wild animals. In ECOWAS space, chimpanzees and some species of bats seem to represent the greatest danger to man taking into consideration transmission risk of the Ebola virus. This study sets the epidemic of Ebola that occurred in 2013 in Guinea into its historical and Panafrican context. Then, it briefly presents the acknowledged role of wildlife in the epidemiology of Ebola and in which ways the environmental changes operate on the known reservoir of this virus. At last, it reminds of the broad outlines of the space-time evolution of the epidemic of Ebola which occurred in ECOWAS space, while trying to reveal the geographical ins and outs of this epidemiological catastrophe

Quel modèle économique pour quel modèle de solidarité ?

Christophe Adam Quand j’ai endossé la responsabilité de trésorier de Médecins du Monde, j’ai réalisé que si nous avions beaucoup réfléchi au processus budgétaire – fait de multiples audits ou de l’attente du résultat de la collecte de fin d’année, un temps extrêmement important pour nous –, nous n’avions sans doute pas suffisamment pensé ce qui se jouait derrière notre modèle économique. Et comme un fait exprès, notre débat se tient le jour où le gouvernement annonce 21 milliards d’économies ..

Three distinct glycosylation pathways are involved in the decoration of Lactococcus lactis cell wall glycopolymers

Extra-cytoplasmic sugar decoration of glycopolymer components of the bacterial cell wall contributes to their structural diversity. Typically, the molecular mechanism that underpins such a decoration process involves a three-component glycosylation system (TGS) represented by an undecaprenyl-phosphate (Und-P) sugar-activating glycosyltransferase (Und-P GT), a flippase, and a polytopic glycosyltransferase (PolM GT) dedicated to attaching sugar residues to a specific glycopolymer. Here, using bioinformatic analyses, CRISPR-assisted recombineering, structural analysis of cell wall-associated polysaccharides (CWPS) through Maldi-Tof MS and methylation analysis, we report on three such systems in the bacterium Lactococcus lactis. On the basis of sequence similarities, we first identified three gene pairs, csdAB, csdCD, and csdEF, each encoding an Und-P GT and a PolM GT, as potential TGS component candidates. Our experimental results show that csdAB and csdCD are involved in Glc side chain addition on the CWPS components rhamnan and polysaccharide pellicle (PSP), respectively, whereas csdEF plays a role in galactosylation of lipoteichoic acid (LTA). We also identified a potential flippase encoded in the L. lactis genome (llnz_02975, cflA) and confirmed that it participates in the glycosylation of the three cell wall glycopolymers rhamnan, PSP, and LTA, thus indicating that its function is shared by the three TGSs. Finally, we observed that glucosylation of both rhamnan and PSP can increase resistance to bacteriophage predation and that LTA galactosylation alters L. lactis resistance to bacteriocin

Distinct and Specific Role of NlpC/P60 Endopeptidases LytA and LytB in Cell Elongation and Division of Lactobacillus plantarum

Peptidoglycan (PG) is an essential lattice of the bacterial cell wall that needs to be continuously remodeled to allow growth. This task is ensured by the concerted action of PG synthases that insert new material in the pre-existing structure and PG hydrolases (PGHs) that cleave the PG meshwork at critical sites for its processing. Contrasting with Bacillus subtilis that contains more than 35 PGHs, Lactobacillus plantarum is a non-sporulating rod-shaped bacterium that is predicted to possess a minimal set of 12 PGHs. Their role in morphogenesis and cell cycle remains mostly unexplored, except for the involvement of the glucosaminidase Acm2 in cell separation and the NlpC/P60 D, L-endopeptidase LytA in cell shape maintenance. Besides LytA, L. plantarum encodes three additional NlpC/P60 endopeptidases (i.e., LytB, LytC and LytD). The in silico analysis of these four endopeptidases suggests that they could have redundant functions based on their modular organization, forming two pairs of paralogous enzymes. In this work, we investigate the role of each Lyt endopeptidase in cell morphogenesis in order to evaluate their distinct or redundant functions, and eventually their synthetic lethality. We show that the paralogous LytC and LytD enzymes are not required for cell shape maintenance, which may indicate an accessory role such as in PG recycling. In contrast, LytA and LytB appear to be key players of the cell cycle. We show here that LytA is required for cell elongation while LytB is involved in the spatio-temporal regulation of cell division. In addition, both PGHs are involved in the proper positioning of the division site. The absence of LytA activity is responsible for the asymmetrical positioning of septa in round cells while the lack of LytB results in a lateral misplacement of division planes in rod-shaped cells. Finally, we show that the co-inactivation of LytA and LytB is synthetically affecting cell growth, which confirms the key roles played by both enzymes in PG remodeling during the cell cycle of L. plantarum. Based on the large distribution of NlpC/P60 endopeptidases in low-GC Gram-positive bacteria, these enzymes are attractive targets for the discovery of novel antimicrobial compounds

Analysis of the Peptidoglycan Hydrolase Complement of Lactobacillus casei and Characterization of the Major γ-D-Glutamyl-L-Lysyl-Endopeptidase

Peptidoglycan (PG) is the major component of Gram positive bacteria cell wall and is essential for bacterial integrity and shape. Bacteria synthesize PG hydrolases (PGHs) which are able to cleave bonds in their own PG and play major roles in PG remodelling required for bacterial growth and division. Our aim was to identify the main PGHs in Lactobacillus casei BL23, a lactic acid bacterium with probiotic properties

Genetic and biochemical characterization of the cell wall hydrolase activity of the major secreted protein of Lactobacillus rhamnosus GG

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