Polysialic acid is aunique carbohydrate that decorates the surface of the neural cell adhesion molecule. Polysialic acidis an onco-developmental antigen, expressed in tumours principally of neuroendocrine origin, notably neuroblastoma,strongly correlating with invasion and metastasis. Polysialylation is regulated by two polysialyltransferase enzymes, PST(ST8SiaIV)and STX(ST8SiaII),withSTX dominant in cancer. Post-development polysialic acid expression is only found at low levels in the brain, thus this could be a novel target for cancer therapy. It is hypothesized that inhibition of polysialyltransferasecould lead to control of tumour dissemination and metastasis.The aims of this thesis were to develop tools and in vitro assays to screen novel polysialyltransferaseinhibitors. A panel of tumour cell lines were characterised in terms of growth parameters (using the MTT assay) and polysialic acid expression. This includes a pair of isogenic C6 rat glioma cells (C6-STX and C6-WT) and naturally polysialic acid expressing neuroblastoma cells(SH-SY5Y). Following this, an in vitro assay was validated to screen modulation of polysialic acid expression by removing pre-existing polysialic acid expression using endoneuraminidase N and evaluated the amount of re-expression of polysialic acid using immunocytochemistry. Then, a functional assay was developed and validated for invasion, the matrigel invasion assay. Cytidine monophosphate (tool compound) significantly reduced polysialic acidsurface expression and invasion. A panel of six novel polysialyltransferase inhibitors was screened for cytotoxicity, polysialic acidsurface expression and invasion. Of the potential polysialyltransferase inhibitorsevaluated, ICT3176 and ICT3172 were identified from virtual screening of Maybridge library and were emerged as the most promising inhibitors, demonstrating significant (p<0.05)reduction in cell-surface polysialic acidre-expression and invasion in polysialic acid expressing cells.Furthermore, the specificity of compounds for polysialyltransferase (α-2,8-sialyltransferase) over othermembers of the wider sialyltransferase family (α-2,3-and α-2,6-sialyltransferases) was confirmed using differential lectin staining. These results demonstrated that small molecule inhibitors as STX is possible and provides suitable in vitrocell based assays to discovery more potent derivatives.

This study is a qualitative case study, with a theory-consuming approach and motive analytical structure that aims to examine Russia's ulterior motives, for the full-scale military invasion of Ukraine in February 2022. The analysis is based on a theoretical framework of two different international relations theories: realism and constructivism. Realism highlights security, military power and the survival of state in the international system while constructivism highlights the interactions between different constructed identities, norms and ideas within the international system. Together with the theoretical framework the analysis uses Kremlin's own statements, to see if it corresponds with the theoretical findings. The study concludes that the two theoretical perspectives complement each other in explaining Russia's ulterior motives and that Kremlin's own statements on Ukraine was able to correspond with the theoretical findings.

Background: Highly infiltrative growth and resistance to radiation as well as chemotherapy contribute to a poor prognosis of glioblastoma. To improve the survival of patients with glioblastoma, further research to uncover the complex signaling network is essential. Due to the central role of the signaling adaptor lamellipodin in nervous system development and cell migration, a function of lamellipodin in glioblastoma is conceivable. However, the specific function of lamellipodin in the invasion and radioresistance of glioblastoma is so far entirely unknown. Therefore, the present work investigates the invasion and radioresistance of glioblastoma cells and the underlying signaling mechanism under the influence of lamellipodin. Material and Methods: Expression of lamellipodin was evaluated in human astrocytes and nine glioblastoma cell lines by Western blot analysis. Localization of lamellipodin in glioblastoma cells was analyzed by applying immunofluorescence staining. The effects of lamellipodin silencing by siRNA on the glioblastoma characteristics invasion, survival, and residual DNA double strand breaks (DSB) upon X-ray irradiation, proliferation, apoptosis, and senescence were investigated. Alterations in molecular signaling were analyzed by phosphoproteome analysis upon control and lamellipodin depletion combined with/-out X-ray irradiation in A172 cells. Colony formation assays were performed after single and double knockdown of lamellipodin and the affected proteins to connect latter findings to clonogenic survival. Direct lamellipodin binding partners were explored using mass spectrometry analysis. Validation of protein-protein interaction was determined by immunoprecipitation and proximity ligation assay. Clonogenic survival assay was performed after triple knockdown of lamellipodin, previous proteins identified by phosphoproteome, and the direct interaction partner of lamellipodin. Hierarchical analysis was performed by analyzing the expression and phosphorylation of the determined proteins by immunoblot. Results: Lamellipodin was shown to be expressed and phosphorylated in varying amounts in the glioblastoma cell culture panel, with a preferential localization in membrane protrusions and the cytoplasm. The siRNA-specific depletion of lamellipodin tremendously decreased glioblastoma invasion and proliferation while exerting no impact on apoptosis or senescence. Moreover, seven of the nine studied glioblastoma cell lines were radiosensitized by lamellipodin silencing without affecting the number of residual DNA double strand breaks, while its overexpression improved radiation survival. Mechanistically, the loss of lamellipodin impaired the phosphorylation of nine proteins (EIF2A, EGFR, FOS, MKK6, NFKBIA, PRKAA2, RSK2, SRC, and TAK1), which are mostly implicated in the EGFR-MAPK signaling. The combinational silencing of lamellipodin and the relevant proteins achieved overall radiosensitization in A172 and U343MG cells. Furthermore, mass spectrometric analysis of lamellipodin immunoprecipitates demonstrated that the lamellipodin interactome alters in response to X ray irradiation conditions. RICTOR was confirmed as a direct linker of lamellipodin to the EGFR-MAPK signaling by immunoprecipitation and proximity ligation assay. In addition, triple depletion of lamellipodin, RICTOR, and EGFR resulted in similar degrees of radiosensitization as reported for lamellipodin knockdown, highlighting their superimposable role in glioblastoma radiation response. In line, lamellipodin silencing increased EGFR expression and phosphorylation, while lamellipodin phosphorylation was decreased upon EGFR deficiency. Conclusion: The results uncover the crucial function of lamellipodin for invasion, proliferation, and radiosensitivity of glioblastoma cells. Based on molecular analyses, lamellipodin was discovered as a determinant of EGFR signaling by interacting with RICTOR. Based on these data, the complexity of the signaling networks conducting radiation survival is broadened by adding the adaptor protein lamellipodin. / Hintergrund: Ein stark infiltrierendes Wachstum und Resistenzen gegenüber Bestrahlung und Chemotherapie tragen zu einer schlechten Prognose des Glioblastoms bei. Um die Therapie des Glioblastoms zu verbessern, ist die weitere Erforschung des komplexen Signalnetzwerkes notwendig. Aufgrund der essentiellen Rolle des Signaladaptors Lamellipodin für die Entwicklung des Nervensystems und der Migration von Zellen ist eine Funktion von Lamellipodin im Glioblastom vorstellbar. Die spezifische Funktion von Lamellipodin in der Invasion und Strahlenresistenz des Glioblastoms ist allerdings bisher völlig unbekannt. Die vorliegende Arbeit untersucht daher die Invasion und Strahlenresistenz von Glioblastomzellen sowie den zugrundliegenden molekularen Mechanismus im Hinblick auf Lamellipodin. Material und Methoden: Die Expression von Lamellipodin wurde in humanen Astrozyten und neun Glioblastom-Zelllinien mittels Western Blot Analyse untersucht. Die Lokalisierung von Lamellipodin in Glioblastomzellen wurde mit Immunfluoreszenzfärbung analysiert. Die Auswirkungen eines Lamellipodin-Knockdown mittels siRNA auf die Glioblastom-Eigenschaften Invasion, Überleben und residuale DNA-Doppelstrangbrüche (DSB) bei Röntgenbestrahlung, Proliferation, Apoptose und Seneszenz wurden untersucht. Veränderungen in molekularen Signalwegen wurden durch Phosphoproteomanalyse nach Kontroll- und Lamellipodin-Knockdown in Kombination mit und ohne Röntgenbestrahlung in A172 Zellen analysiert. Koloniebildungsassays wurden nach einfachem und doppeltem Knockdown von Lamellipodin und den betroffenen Proteinen durchgeführt, um letztere Ergebnisse mit dem klonogenen Überleben in Verbindung zu bringen. Direkte Lamellipodin-Bindungspartner wurden mittels massenspektrometrischer Analyse untersucht. Die Validierung der Protein-Protein-Interaktion wurde durch Immunpräzipitation und Proximity Ligation Assay bestimmt. Ein klonogenes Überlebensassay wurde nach dreifachem Knockdown von Lamellipodin, durch das Phosphoproteom identifizierten Proteinen und dem direkten Interaktionspartner von Lamellipodin durchgeführt. Die hierarchische Analyse erfolgte durch Analyse der Expression und Phosphorylierung der ermittelten Proteine mittels Immunblot. Ergebnisse: Die Expression und Phosphorylierung von Lamellipodin war unterschiedlich in den Glioblastomzelllinien. Die siRNA-vermittelte Deletion von Lamellipodin verringerte die Invasion und Proliferation von Glioblastomzellen enorm, während die Reduktion von Lamellipodin keine Auswirkungen auf Apoptose oder Seneszenz hatte. Darüber hinaus wurden sieben der neun untersuchten Glioblastomzelllinien durch das Ausschalten von Lamellipodin radiosensibilisiert, ohne dass sich dies auf die Anzahl der residualen DNA-Doppelstrangbrüche auswirkte, während die Überexpression von Lamellipodin das Überleben nach Bestrahlung verbesserte. Mechanistisch beeinträchtigte der Verlust von Lamellipodin die Phosphorylierung von neun Proteinen (EIF2A, EGFR, FOS, MKK6, NFKBIA, PRKAA2, RSK2, SRC und TAK1), die hauptsächlich an der EGFR-MAPK-Signalübertragung beteiligt sind. Die kombinierte Ausschaltung von Lamellipodin und den relevanten Proteinen führte zu einer allgemeinen Radiosensibilisierung in den Zelllinien A172 und U343MG. Darüber hinaus zeigte die massenspektrometrische Analyse von Lamellipodin-Immunpräzipitaten, dass sich das Lamellipodin-Interaktom als Reaktion auf Röntgenbestrahlung verändert. RICTOR wurde durch Immunpräzipitation und Proximity Ligation Assay als direktes Bindeglied von Lamellipodin zum EGFR-MAPK-Signalweg identifiziert. Darüber hinaus führte die dreifache Deletion von Lamellipodin, RICTOR und EGFR zu einem ähnlichen Grad an Radiosensibilisierung wie der Knockdown von Lamellipodin, was ihre gemeinsame Rolle bei der Strahlenreaktion von Glioblastomen unterstreicht. Darüber hinaus erhöhte die Ausschaltung von Lamellipodin die EGFR-Expression und -Phosphorylierung, während die Lamellipodin-Phosphorylierung bei EGFR-Mangel verringert wurde. Schlussfolgerung: Die Ergebnisse decken die entscheidende Funktion von Lamellipodin für die Invasion, Proliferation und Radiosensitivität von Glioblastomzellen auf. Basierend auf molekularen Analysen wurde Lamellipodin als eine Determinante der EGFR-Signalübertragung durch Interaktion mit RICTOR identifiziert. Auf der Grundlage dieser Daten wird die Komplexität des Signalnetzwerks, welches das Überleben durch Strahlung reguliert, durch das Adaptorprotein Lamellipodin erweitert.

Abstract   Title: Standardization or differentiation? - A study on companies' maintenance of legitimacy in times of war.   Level: Bachelor's thesis in Business Administration. Authors: Evelina Enander Sjökvist and Nina Olsson Islani. Supervisor: Asif M Huq. Date: May 2024.   Aim: "The purpose of the study is to examine the impact of war on companies' maintenance of legitimacy. How Nordic companies operating in Russia have communicated regarding this crisis to uphold their legitimacy".   Method: A qualitative research method with an abductive approach has been chosen in the form of a document study. A content analysis will be used on documents obtained from the Retriever database or companies websites.   Results and Conclusions: The results show that companies use different strategies when it comes to crisis management of the war between Russia and Ukraine. Clear standardization and differentiation exist both between companies and industries, showing their unique strengths and standards that the companies adhere to. A central conclusion that has characterized the study from the beginning is that this concerns sensitive information.   Contributions: The study has contributed to the research area of companies maintaining legitimacy in times of war and crisis management, the study focuses on companies that have acted in the war. An additional contribution is the analysis model that has been constructed.   Suggestions for future research: A suggestion for further research is to study the full consequences of the war and the sensitivity of information over time. It would be interesting to conduct a study focusing on comparing different years in the annual reports. / Sammanfattning    Titel: Standardisering eller differentiering? - En studie om företags bibehållande av legitimitet i krigstider.    Nivå: Kandidatuppsats i företagsekonomi. Författare: Evelina Enander Sjökvist och Nina Olsson Islani. Handledare: Asif M Huq. Datum: Maj 2024.    Syfte: “Studiens syfte är att studera krigets påverkan på företagens bibehållande av legitimitet. Hur nordiska företag med verksamhet i Ryssland kommunicerat angående denna kris för att upprätthålla sin legitimitet”.   Metod: En kvalitativ forskningsmetod med en abduktiv ansats har valts i form av en dokumentstudie. En innehållsanalys kommer att användas på dokument inhämtade från databasen Retriever och företags webbsidor.        Resultat och Slutsats: Resultaten visar på att företag använder sig av olika strategier när det gäller krishantering av kriget mellan Ryssland och Ukraina. Tydlig standardisering och differentiering finns både mellan företag och branscher, som visar på deras unika styrkor och standarder som företagen förhåller sig till. En central slutsats som präglat studien från början är att detta gäller känslig information.     Bidrag: Studien har bidragit till forskningsområdet kring företags bibehållande av legitimitet i krigstider samt krishantering då studien riktar sig mot företag som agerat gentemot kriget. Ett ytterligare bidrag till framtida forskning är den analysmodell som konstruerats.     Förslag till vidare forskning: Förslag till vidare forskning är att studera krigets fullständiga konsekvenser samt informationens känslighet längre fram i tiden. Det hade varit intressant att utföra en studie där jämförelse mellan olika årtal på årsredovisningarna varit i fokus.

Species that become naturalized in a new geographical range, subsequently multiply and spread, and persist to the detriment of resident communities, are known as alien invasive species. Two aspects of species invasion – spread and ecological impact – were examined using Lantana camara L. (henceforth lantana) as the study system, specifically in the context of a seasonally dry tropical forest ecosystem of the Mudumalai Wildlife Sanctuary and National Park. Lantana is a thicket-forming woody shrub of South and central American origin, which is now widespread across the tropics. The thesis is divided broadly into two parts -the first part examines the influences of environmental factors on the distribution and spread of lantana while the second part focuses on the effects of lantana on the distribution, survival and growth of native woody species. Much of the work presented in this thesis was conducted within a 50 ha permanent plot (the Mudumalai Forest Dynamics Plot, MFDP hereon) in Mudumalai, chiefly because the history of invasion by lantana has been recorded here since 1989. The influence of changing resources on lantana invasion was explored at two scales -small spatial but fine temporal scale in the MFDP and at the level of the landscape. Available data on an 18 year chronosequence of changes in the qualitative density of lantana from the MFDP and field studies between the years 2009 and 2010 were used to determine the environmental correlates of lantana spread in time and space. It was found that biotic factors such as the presence of the shrub Helicteres isora and abiotic factors such as proximity to drainages and the combination of fire and drought promoted the intensification of lantana invasion in time while proximity to streams, higher total annual rainfall and low fire frequency contributed to lantana invasion at the landscape level. The impacts of lantana on the seedlings of native woody species were assessed in 10m x 10m plots within the MFDP. An initial enumeration of 60 such plots revealed that animaldispersed, dry forest habitat preferring species were most affected by the presence of dense lantana. A follow-up study comprising of growth and survival measurements made on 1105 seedlings over two years (2008-2010) further confirmed that dry forest preferring species were most affected by the presence of dense lantana and that this response at the community level was most likely influenced by the most abundantly sampled species in this habitat preference guild – Catunaregam spinosa. In conclusion, while the environmental correlates of lantana most likely promoted its invasion, only certain guilds of native species seemed to be negatively affected by the presence of lantana.

L'acarien rouge de la tomate Tetranychus evansi (Tetranychidae) est considéré comme une espèce invasive à fort impact économique sur les cultures de solanacées. Il a été découvert pour la première fois en 1954 au Brésil, d'où il est probablement originaire. Historiquement, T. evansi a d'abord été signalé en Afrique et plus récemment en Europe et en Asie. L'objectif de cette thèse était de reconstruire les routes de colonisation de T. evansi et de dégager le scénario évolutif décrivant le mieux l'histoire de l'invasion. Nous avons d'abord analysé des échantillons collectés dans son aire actuelle de distribution, à l'aide des séquences d'un fragment du gène codant pour la sous-unité I de la Cytochrome Oxydase (COI) de l'ADN mitochondrial et de la région ITS1-5,8S-ITS2 de l'ADN nucléaire ribosomique. Les données soutiennent l'hypothèse d'une origine sud américaine de cette espèce et ont révélé que des événements d'invasions multiples et cryptiques ont eu lieu lors de la colonisation de l'Europe. L'invasion résulte de deux lignées génétiquement divergentes et originaires de deux régions géographiques distantes au Brésil. Ces deux lignées semblent avoir des potentiels invasifs contrastés. Elles s'hybrident au laboratoire ainsi que dans la nature. Grâce à 16 locus microsatellites que nous avons développés et utilisés comme marqueurs, nous avons déterminé les zones géographiques de cette hybridation. Nous avons également pu estimer des paramètres historiques de l'invasion et confronter différents scénarios d'introduction, par la comparaison de la composition génétique des populations récemment introduites avec celles de l'aire d'origine de T evansi, et par l'utilisation de la méthode d'inférence bayésienne (Approximate Bayesian Computation, ABC). Les résultats ABC contredisent partiellement le scénario d'invasion basé uniquement sur des données historiques. Ils suggèrent que T. evansi serait d'abord arrivé en Europe dans le sud de l'Espagne (en Andalousie) bien avant les signalements historiques. Ainsi, l'Andalousie semble avoir servi de source de colonisation pour des nouvelles zones en Afrique, d'autres régions méditerranéennes et d'Asie. Les résultats de cette thèse ouvrent des perspectives d'étude visant à comprendre pourquoi certaines populations d'une espèce allochtone réussissent à s'établir et à envahir un nouvel écosystème / The red tomato spider mite Tetranychus evansi (Tetranychidae) is regarded as an invasive species having an important economic impact on solanaceous crops. It was first discovered in Brazil in 1954, where it probably originated. Based on historical records, T. evansi was first reported in Africa and more recently in Europe and Asia. This work aims at reconstructing the colonization routes of T. evansi and identifies the scenario that best describes the evolutionary history of the invasion. To do this, we first analyzed samples collected from most parts of the world where the mite is currently known to occur. We used sequence variation of a fragment of the mitochondrial Cytochrome Oxidase I (COI) sub-unit I gene and the ITS1-5.8S-ITS2 of the nuclear ribosomal DNA. Our results were consistent with the hypothesis of a South American origin of this species. They also suggested that the invasion of south Europe resulted from multiple cryptic introductions from two genetically divergent lineages originated from two distant geographical regions in Brazil. These two lineages seem to have a differential invasive potential. Despite the high genetic divergence, crosses between mites stemming from the two lineages do occur both in the laboratory and in nature. Second, we used 16 microsatellite loci that we developed for this study and in association with Approximate Bayesian Computation (ABC) methods; we reconstructed the historical events of the cryptic invasion of the pest. ABC results challenge the invasion scenario captured by historical data only. They suggest that T. evansi first arrived to Europe in Southern Spain (Andalusia) long before historic records. Thus, Andalusia seems to have served as a source for colonization of new areas in Africa and other Mediterranean regions. The results obtained in this thesis provide an interesting framework to further study and understand why some populations of an exotic species might become invasive.

Le cancer épithélial de l’ovaire (CÉO) est le cancer gynécologique le plus létal. Bien que certains progrès aient été accomplis, une meilleure compréhension des mécanismes moléculaires impliqués dans le développement de ce cancer est requise. Notre laboratoire a démontré que la protéine tyrosine phosphatase DEP-1 était impliquée dans l’activation de Src, la survie, la migration et l’invasion des cellules endothéliales en réponse au VEGF. Des études ont proposé que Src ait également un rôle important dans la progression tumorale du CÉO. Ainsi, nous nous intéressons au rôle de DEP-1 dans le potentiel invasif du CÉO. Nous avons observé des niveaux d’expression variables de DEP-1 dans 6 lignées cellulaires du CÉO et constaté que ceux-ci corrèlent positivement avec le potentiel invasif des cellules dans le Matrigel. Des expériences d’ARNi ont démontré que la réduction de l’expression de DEP-1 inhibe des voies de signalisation pro-invasives telles que la phosphorylation de Src et de Cortactine, ainsi que la localisation de Cortactine aux lamellipodes. Cette déplétion de DEP-1 a également eu pour effet de diminuer d’autres voies de signalisation pro-tumorales, tel que la phosphorylation de l’EGFR et de P65 (NfκB). Conséquemment, la déplétion de DEP-1 par transfection d’ARNi se traduit par une perte du potentiel invasif des cellules, et une diminution de la résistance des cellules au Carboplatin. L’analyse de l’expression de DEP-1 par immunohistochimie dans les tumeurs ovariennes révèle l’existence d’une corrélation positive entre l’expression en protéine de DEP-1 et le cancer de l’ovaire de grade élevé et la survie des patientes, qui a également été confirmé sur une puce à ARN. Nos résultats suggèrent que DEP-1 favoriserait la progression tumorale du cancer épithélial de l’ovaire. Nous avons démontré que DEP-1 est impliquée dans l’invasion in vitro, et que son expression est associée à un cancer de l’ovaire plus agressif, faisant ainsi de DEP-1 une cible thérapeutique potentiellement intéressante. / Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. Our laboratory has previously shown that the protein tyrosine phosphatase DEP-1 is involved in Src activation, survival, migration and invasion of endothelial cells in response to VEGF. Studies have shown that Src may be implicated in the progression of epithelial ovarian cancer progression. Thus, we were interested in determining if DEP-1 had a role in the promotion of the Src invasive pathway in EOC. First, we have observed a variable protein expression of DEP-1 in six EOC cell lines, and that there was a positive correlation with invasion in Matrigel. We also showed in RNAi experiments that inhibition of DEP-1expression resulted in the decreased phosphorylation of Src and Cortactin, also loss of Cortactin localisation at the cellular membrane. We also observed dysregulation of other pro-tumoral pathways like EGFR and P65 (NfκB) diminution of phosphorylation. Consequently, DEP-1 depletion resulted in loss of invasive capacities of most of the cell lines, and diminution of chemoresistance in response to Carboplatin. Analysis of DEP-1 in EOC tumors revealed the existence of a positive correlation with an aggressive form of ovarian cancer, high grade status, and poorer survival. These results suggest a positive role of DEP-1 in tumor progression of EOC. Our results show for the first time that DEP-1 is implicated in invasion in vitro, and is associated with the most aggressive form of EOC. Thus, DEP-1 is an interesting therapeutical target for EOC.

Les infections à Salmonella Typhimurium constituent un problème de taille pour l’industrie porcine et la santé publique car cet animal est un réservoir pour les infections chez l’homme. De plus, on observe, chez des souches appartenant au lysotype (LT) 104, des résistances multiples aux antimicrobiens associées à des septicémies chez les porcs en engraissement, ce qui peut contribuer à la contamination des carcasses. Il faut donc contrôler l’infection au niveau du troupeau. Pour ce faire, il importe donc de mieux caractériser ces souches, comprendre la pathogénie de l’infection et identifier des facteurs de virulence. L’objectif principal de cette étude était de caractériser des isolats de S. Typhimurium provenant de porcs septicémiques et de les comparer avec ceux de porcs sains. Une banque d’isolats provenant de porcs septicémiques (ASC) et de porcs sains à l’abattoir (SSC) était constituée. Le lysotype des isolats a été identifié et ceux-ci ont été caractérisés selon le profil de résistance aux antimicrobiens, le SDS-PAGE et l’immunobuvardage et le PFGE. Chez les isolats ASC, LT 104 représentait 36.4% des isolats et chez les isolats SSC la proportion était de 51.5%. Les isolats pouvaient être résistants jusqu’à douze antimicrobiens, peu importe leur origine. Il n’a toutefois pas été possible d’associer une protéine spécifique au groupe d’isolats ASC. Parmi les souches LT 104, plusieurs groupes génétiques ont été identifiés. Les différentes étapes de la pathogénie de Salmonella ont ensuite été évaluées, dont l’adhésion et l’invasion des isolats des deux banques sur des cellules intestinales humaines. Nos résultats ont démontré que les isolats ASC avaient un pouvoir accru d’invasion comparés aux isolats SSC (P=0.003). Pour un sous-groupe d’isolats sélectionnés selon leur taux d’invasion, des tests de phagocytose, d’apoptose et d’adhésion au mucus intestinal ont été effectués en utilisant la cytométrie en flux. La survie des bactéries après la phagocytose a aussi été évaluée et la méthode MATS a été utilisée pour évaluer l'adhésion aux solvants. Les pourcentages de phagocytose chez les isolats SSC par les monocytes porcins étaient plus élevés que chez les isolats ASC à 15 minutes (P=0.02). Nous n’avons trouvé aucune différence significative pour les autres méthodes utilisées. Nous avons ensuite comparé le génome d’un isolat ASC (#36) à celui d’un isolat SSC (#1) par le SSH pour identifier des facteurs de virulence potentiels. Des clones correspondant à des gènes retrouvés sur le chromosome ainsi que sur des plasmides ont été identifiés. Ces résultats nous ont dirigés vers l’analyse des profils plasmidiques de tous les isolats. Les différents profils étaient retrouvés autant chez les isolats ASC que chez les isolats SSC. Deux profils (PL14 et PL20) étaient observés plus fréquemment chez les isolats LT 104 que chez les isolats d’autres lysotypes (P=0.01 et P=0.01, respectivement). Le séquençage d’un des plasmides de l’isolat ASC, démontrait la présence d’informations génétiques codant pour la réplication et une bêta-galactosidase-α. Il serait intéressant de préciser le rôle exact de ces gènes dans l’infection. Nos travaux suggèrent que les isolats de S. Typhimurium provenant de porcs septicémiques se distinguent par un pouvoir d’invasion accru ainsi que par des taux de phagocytose plus faibles dans les phases initiales de l’infection. Cette étude aura donc permis d’accroître les connaissances sur la pathogénie des infections à S. Typhimurium chez le porc. / Salmonella Typhimurium infections represent an important threat both to the swine industry and public health since pig is also a reservoir for human infections. Multiresistance to antimicrobial agents is often associated with S. Typhimurium belonging to phage type (PT) 104, and these isolates can cause septicemia in fattening pigs. It is thus necessary to control the infection at the herd level to avoid meat contamination by these isolates. However, in order to develop more efficacious control measures, it is important to characterize isolates, better understand the pathogenesis of infection and identify virulence factors. The main objective of this study was to characterize isolates of S. Typhimurium associated with septicemia in swine and to compare them to isolates recovered from healthy pigs. Isolates of S. Typhimurium associated with septicemia in swine (CS) were compared to isolates recovered from healthy animals at slaughterhouses (WCS). The phage type of each isolate was identified and these isolates were characterized by antimicrobial resistance, SDS-PAGE and immunoblotting, and PFGE. Among the CS isolates, PT 104 represented 36.4% of isolates while it represented 51.5% of WCS isolates. Resistance to as many as twelve antimicrobial agents was found in isolates from CS and WCS. However, it was not possible to associate any particular protein to septicemic isolates. Multiple genetic profiles were identified among the isolates of PT 104. Different steps of the pathogenesis of Salmonella infection were evaluated, in particularly the ability to adhere to and invade intestinal epithelial cell lines by CS and WCS isolates. The isolates recovered from diseased animals invaded intestinal epithelial cell lines at a higher rate than isolates from healthy pigs (P=0.003). Some isolates were selected according to their invasion rate and some analysis, using flow cytometry were done to evaluate phagocytosis, induction of apoptosis, and adhesion to intestinal mucus. The survival in monocytes was evaluated and the MATS method was used to evaluate the bacterial surface properties, measuring interactions with solvents. Isolates from WCS were more phagocytized than isolates fom CS at 15 minutes (P=0.02). We found no significant difference for the other methods used. Using SSH, we also compared the genome of a CS isolate (#36) to that of a WCS isolate (#1), for the identification of putative virulence factors. Clones with chromosome and plasmids homology were obtained. It was therefore decided to analyze the plasmid profiles of all isolates. Two profiles (PL14 and PL20) were more frequently observed in the PT 104 isolates than in the isolates belonging to other phage types (P=0.01 and P=0.01, respectively). Various profiles were found in both isolates from septicemic pigs and those from healthy pigs. An interesting plasmid of the CS isolate was sequenced. This plasmid possesses genetic information for replication as well as a beta-galactosidase-α. It would be needed to characterize the role of these putative virulence factors in the future. Our work suggests that isolates from septicemic pigs may be distinguished from isolates from healthy pigs by their better ability to invade intestinal cells as well as by a lower rate of phagocytosis in the early steps of infection. This study increased our knowledge on the pathogeny of S. Typhimurium infection in pigs.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.

Thèse numérisée par la Division de la gestion de documents et des archives de l'Université de Montréal.