Introducing Shear Stress in the Study of Bacterial Adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm2. Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm2). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes 1. On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm22. The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium 3. To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber 4. Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells 1, to proliferate on the cell surface 5and to detach to colonize new sites 6 (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience1 and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study

DÖNNINGHAUS, Victor, Revolution, Reform und Krieg. Die Deutschen an der Wolga im ausgehenden Zarenreich

À la veille de la Grande Guerre, près de 500 000 Allemands, répartis en environ 200 colonies, vivaient dans la région de la Volga, dans les districts de Saratov et Samara où ils formaient entre 7 et 8% de la population. V.D. leur consacre une dense et riche étude, explorant la situation sociale et politique de ces communautés entre 1905 et 1917, une période charnière inscrite entre guerres, révolutions et modernisation. Il dresse le constat de la grande précarité économique de ces populations..

Activities of Daily Living

Duménil Gérard. Le nouvel ordre néolibéral : pouvoir de classe contre solidarité nationale. In: Raison présente, n°159, 3e trimestre 2006. L'idée de nation. pp. 31-42

BERDING, Helmut, HELLER, Klaus, SPEITKAMP, Winfried, Krieg und Erinnerung. Fallstudien zum 19. und 20. Jahrhundert

Issus d’une table ronde organisée en février 1999 par les chercheurs du Sonderforschungsbereich de l’université de Gießen, les articles de ce volume étudient le rôle des guerres dans la genèse et les formes d’expression de la mémoire collective. Interrogeant les spécificités confessionnelles de la culture de guerre de 1870, C. RAK s’intéresse à l’expérience de guerre des aumôniers catholiques du diocèse de Rottenburg. S’ils affirment la légitimité d’un conflit conçu comme défensif, ils ignor..

HINZ, Uta, Gefangen im Großen Krieg. Kriegsgefangenschaft in Deutschland 1914-1921

Au moins 7 millions, peut-être 9 millions d’hommes, soldats et officiers, furent fait prisonniers pendant la Grande Guerre. Alors que la captivité de guerre constitua un des enjeux importants du conflit, tant au plan stratégique ou économique qu’imaginaire, le thème fut longtemps délaissé par l’historiographie. Ces « oubliés de la Grande Guerre », pour reprendre la juste expression d’Annette Becker, retiennent actuellement l’attention, peut-être parce que la captivité de guerre livre un assez..

Le faciès céramique d'un atelier sidérurgique présumé d'epoque flavienne à arancou (Pyrénées-Atlantiques)

L’étude céramologique du site d’Arancou – Las Courrèges (Pyrénées‐ Atlantiques, France), outre corroborer les données archéologiques ayant révélé une occupation datant de la seconde moitié du Ier s. ‐ IIème s. de notre ère, vient offrir de nouvelles données et correspondances statistiques sur le faciès de consommation ainsi que de nouveaux profils, notamment unepassoire, contribuant à affirmer à la fois la richesse mais aussi la diversité des activités s´étant déroulé sur le site. Elle offre de nouveaux contrastes sur l’occupation de cette extrémité de l’Aquitaine méridionale relativement peu documentée et des exploitations, notamment métallurgiques, qui ont pu s’y dérouler.El estudio del material cerámico de la excavación arqueológica de Arancou – Las Courrèges (Pyrénées‐Atlantiques, Francia) viene a confirmar los análisis arqueológicos, revelando una ocupación que data de la segunda mitad del siglo I d.C. ‐ inicios del siglo II d.C. Además, nos ofrece nuevos datos y nueva información estadística sobre la facies de consumo así como sobre nuevos perfiles, entre los que destacamos un colador. Esto nos permite definir tanto la identidad social de los ocupantes como la abundancia de actividades en el sitio. El estudio pone de relieve nuevos contrastes en el conocimiento que tenemos sobre la ocupación de este extremo de Aquitania meriodional, un área relativamente poco documentada, y sobre las actividades y explotaciones agrícolas que pudieron llevarse a cabo, especialmente la metalúrgica

A Poisson sample of a smooth surface is a good sample

International audienceThe complexity of the 3D-Delaunay triangulation (tetrahedralization) of n points distributed on a surface ranges from linear to quadratic. When the points are a deterministic good sample of a smooth compact generic surface, the size of the Delaunay triangulation is O(n log n). Using this result, we prove that when points are Poisson distributed on a surface under the same hypothesis, whose expected number of vertices is λ, the expected size is O(λ log^2 λ)

Un échantillon de Poisson d’une surface est un bon échantillon

The complexity of the Delaunay triangulation of $n$ points distributed ona surface ranges from linear to quadratic. When the points are a deterministic good sample of a smooth compact generic surface, the size of the Delaunay triangulationis $O(n\log n)$ [Attali et al.]. Using this result, we prove that when points are Poisson distributedon a surface under the same hypothesis, with intensity $\lambda$, the expected size is $O(\lambda \log^2 \lambda)$

Stochastic Analysis of Empty-Region Graphs

International audienceGiven a set of points $X$, an empty-region graph is a graph in which $p$, $q \in X$ are neighbors if some region defined by $(p, q)$ does not contain any point of $X$. We provide expected analyses of the degree of a point and the possibility of having far neighbors in such a graph when $X$ is a planar Poisson point process. Namely the expected degree of a point in the empty axis-alignedellipse graph for a Poisson point process of intensity $\lambda$ in the unit square is $\Theta(\ln\lambda)$. It is $\Theta(\ln\beta)$ if the ellipses are constrained to have an aspect ratio between 1 and $\beta>1$, and $\Theta(\beta)$ when the aspect ratio is constrained but ellipses are not axis-aligned