Mémoire numérisé par la Direction des bibliothèques de l'Université de Montréal.

Natural products continue to be a valuable source of compounds in research involving chemical ecology and drug discovery. Secondary metabolites are biosynthesized to benefit the host organism in its environment (feeding deterrence from predators, antibiotic properties to avoid infection, etc.) but these compounds also serve as useful scaffolds in drug discovery applications. The research herein describes both aspects of these two branches of natural products chemistry. The Antarctic sponge Dendrilla membranosa produces diterpenes, of which membranolide A, deters feeding of the predatory amphipod Gondogenia antarctica. A metabolomic study of several sponges was undertaken to determine environmental factors that govern the metabolism of D. membranosa. Habitat specificity, above or below the algal canopy, was a significant factor for the chemical clustering of sponges as well as the abundance of potential amphipod predators that are prevalent within the canopy. Another D. membranosa diterpene, aplysulphurin, undergoes degradation upon methanolic treatment to form the methoxy membranolides B-H. An investigation of these artifacts reveals potent activity against the leishmaniasis-causing parasite Leishmania donovani. Microorganisms also generate a significant number of bioactive natural products. Biotic and abiotic culture stressors such as co-culturing and epigenetic modification, respectively, will be explored to turn on cryptic biosynthetic pathways. These techniques are shown to produce unique secondary metabolites from cultures and further reinforce the one strain many compounds approach to the versatile and formidable microbial domain.

The relationship between the cellulolytic Clostridium termitidis and the electrogenic Geobacter sulfurreducens was evaluated in terms of co-culture sustainability and hydrogen production. Batch co-culture experiments in triplicate balch tubes were conducted using cellobiose as the sole carbon source and fumarate as a terminal electron acceptor. Despite high initial concentrations of acetate, no formate and very low H2 concentrations were detected, supporting the hypothesis that a syntrophic association exists between both bacteria. Co-culture growth characterization experiments were repeated in three microbial electrolysis cells and cellobiose as the sole carbon source. Initially, 9.7 mol-H2 mol-1-glucose was produced. However, a sustainable co-culture could not be maintained despite efforts to reduce reactor temperature and triple the medium’s buffering capacity. Strategies to achieve a sustainable co-culture are to minimize the carbon flux through C. termitidis by using complex substrates, maintain neutral operating conditions, and introduce acetogenic bacteria to control the flux of metabolic intermediates.

The relationship between the cellulolytic Clostridium termitidis and the electrogenic Geobacter sulfurreducens was evaluated in terms of co-culture sustainability and hydrogen production. Batch co-culture experiments in triplicate balch tubes were conducted using cellobiose as the sole carbon source and fumarate as a terminal electron acceptor. Despite high initial concentrations of acetate, no formate and very low H2 concentrations were detected, supporting the hypothesis that a syntrophic association exists between both bacteria. Co-culture growth characterization experiments were repeated in three microbial electrolysis cells and cellobiose as the sole carbon source. Initially, 9.7 mol-H2 mol-1-glucose was produced. However, a sustainable co-culture could not be maintained despite efforts to reduce reactor temperature and triple the medium’s buffering capacity. Strategies to achieve a sustainable co-culture are to minimize the carbon flux through C. termitidis by using complex substrates, maintain neutral operating conditions, and introduce acetogenic bacteria to control the flux of metabolic intermediates.

A huge discrepancy between the number of patients on the waiting list for organ transplants and the actual available donors has led to search for alternative approaches to substitute compromised or missing tissues and organs. Tissue engineering is a promising alternative to organ transplantation with the aim to fabricate functional organs through the use of biological or biocompatible scaffolds. Nanogels made from self-assembling ultrashort peptides are promising biomaterials for a variety of biomedical applications. Our group at KAUST is interested in the development of novel synthetic peptide-based biomaterials that combine the advantages of both natural and synthetic hydrogels for various applications. In this study, we have investigated two compounds of a novel class of rationally designed ultrashort peptides, Ac-IVFK-NH2 (Ac-Ile-Val-Phe-Lys-NH2) and Ac-IVZK-NH2 (Ac-Ile-Val-Cha-Lys-NH2). These compounds have an innate tendency to self-assemble into nanofibrous hydrogels which can be used as 3D scaffolds, for example for the fabrication of 3D skin grafts for wound healing. We have evaluated the efficacy of the peptide scaffolds in treating full-thickness wounds in minipigs. Additionally, we assessed the ability of these scaffolds in supporting skeletal muscle tissue proliferation and differentiation. We found that our innovative nanogels supported a substantial increase in human dermal fibroblast and myoblast growth and cells viability, and supported myoblast differentiation. Also, microscopic observation of the direct contact of keratinocytes and fibroblasts revealed enhancement in keratinocytes proliferation. In addition, we demonstrated the ability of human umbilical vein endothelial cells to form tube like structure within peptide nanogels using immunofluorescence staining. Moreover, we successfully produced artificial 3D vascularized skin substitutes using these peptide scaffolds. We selected these peptide nanogels and were able to produce in situ silver nanoparticles within the nanogels, solely through UV irradiation, with no reducing agent present. We then assessed the efficacy of the silver nanoparticle-containing peptide nanogels on minipigs with full-thickness excision wounds. The application of the peptide nanogels on full thickness minipig wounds demonstrated that the scaffolds were biocompatible and did not trigger wound inflammation, and thus safe for topical application. The effect of nanogels, both with and without the addition of the silver nanoparticles, revealed that the scaffold itself has a high potential to act as an antibacterial agent. Interestingly, the effect of the peptide nanogels on wound closure was comparable to that of standard care hydrogels. Furthermore, we have demonstrated that both peptides can act as printable bioinks which opens up the possibility of 3D bioprinting of different cell types in the future. We believe that the described results represent an advancement in the context of engineering skin and skeletal muscle tissue, thereby providing the opportunity to rebuild missing, failing, or damaged parts.

Ce projet de thèse se propose d’évaluer le devenir, la cytotoxicité et la réponse inflammatoire pulmonaire in vitro suite à l’exposition aux nanoparticules, et plus particulièrement vis-à-vis de la région alvéolaire.Les nanoparticules étudiées sont formulées à base d’acide poly (lactide-co-glycolide) (PLGA) (polymère biodégradable), stabilisées, ou non, par différents polymères de surface (alcool polyvinylique (PVA), chitosane (CS), pluronic F68 (PF68)). Les nanoparticules ont une taille d’environ 200 nm, et présentent des charges de surface neutre (PLGA/PVA), positive (PLGA/CS) ou négative (PLGA/PF68 et PLGA sans stabilisant). Des nanoparticules non-biodégradables de dioxyde de titane (TiO2) et de polystyrène ont été choisies comme contrôle positif. Pour mimer les conditions alvéolaires, la lignée cellulaire A549 d’épithélium alvéolaire humain a été utilisée en mono-culture et en co-culture en contact direct avec des macrophages différenciés de monocytes humains (lignée THP-1). Les caractérisations phénotypique et microscopique de la co-culture, ont confirmé la présence de deux types cellulaires viables et en contact. Le CD14, récepteur membranaire exprimé uniquement par les macrophages, sera utilisé pour identifier chaque sous-population cellulaire. D’autre part, l’analyse du récepteur CD54 a montré la présence d’interactions intercellulaires en co-culture : exprimé uniquement par les macrophages en mono-culture, il est exprimé par les deux sous-populations cellulaires en co-culture. Ces interactions ont été confirmées lors de la quantification des cytokines sécrétées après exposition au lipopolysaccharide: les niveaux de sécrétions en co-culture étant jusqu’à 5 fois supérieurs aux niveaux théoriques (issus de la somme des sécrétions en mono-culture).L’analyse en microscopie confocale a confirmé que les nanoparticules sont internalisées par chaque type cellulaire, Les cinétiques d’internalisation suivies en cytométrie en flux ont montré que les nanoparticules de charge de surface négative sont internalisées en plus grande quantité que les autres, quelque soit le type cellulaire, en mono ou en co-culture, selon un mécanisme énergie-dépendant. Enfin, en co-culture, les macrophages internalisent davantage de nanoparticules que les cellules épithéliales.La cytotoxicité des nanoparticules a été évaluée par la mesure de l’activité mitochondriale, l’étude de l’intégrité membranaire, et le type de mort cellulaire. Les résultats montrent qu’à faible concentration toutes les nanoparticules de PLGA induisent une cytotoxicité généralement faible (60 à 80 % de viabilité), avec une mort exclusivement nécrotique, sans induire de forts dommages à la membrane. La toxicité des nanoparticules de PLGA/CS peut être expliquée par la toxicité propre du chitosane. A forte concentration, le cas des nanoparticules de PLGA sans stabilisant mérite d’être noté, car elles n’induisent aucune cytotoxicité vis-à-vis des macrophages, contrairement aux nanoparticules stabilisées. La cytotoxicité des nanoparticules de TiO2 est plus importante, mais peu de dommages à la membrane sont causés. La réponse inflammatoire a été évaluée par la quantification des cytokines sécrétées après 24 h d’exposition aux nanoparticules (0,1 mg/mL). En mono-culture, seules les nanoparticules de PLGA/PF68 induisent une réponse inflammatoire sur les cellules A549, corrélée à leur plus grande internalisation. En co-culture, la réponse inflammatoire est peu prononcée. En revanche, ni les polymères de surface ni les nanoparticules de PLGA sans stabilisant, n’induisent de réponse inflammatoire spécifique.Ces résultats montrent la faible toxicité des nanoparticules de PLGA vis-à-vis des conditions alvéolaires, et soulignent l’importance du recouvrement de surface. En conclusion, les nanoparticules de PLGA testées présentent un fort intérêt pour une application biomédicale, modulée par l’ajustement des propriétés de surface. / The pulmonary route has attracted great attention for the delivery of nanomedicines due to the non invasiveness, a weak enzymatic activity and potential alveolar retention and/or absorption. However, the potential pulmonary toxicity of nanoparticles raises a lot of concern, especially for manufactured, non-biodegradable nanoparticles. In this study, we design and characterize an in vitro model of lung epithelium based on a co-culture of alveolar epithelial-like cells (A549) and macrophages (differentiated from THP-1 monocytes), and use it to assess the potential toxicity of various biodegradable nanoparticles in the form of nanocarriers, as compared to non-biodegradable nanoparticles used in manufactured products. The ultimate goal is to provide a safety pattern of nanoparticles relevant for drug delivery to the lung.The co-culture was characterized by flow cytometry (analysis of three cell membrane receptors: CD14, CD11b and CD54) and confocal laser scanning microscopy. The presence of two different cell types was evidenced, as well as several cellular interactions. For instance, after exposure to a pro-inflammatory compound, synergistic effects were observed, in terms of cytokine secretions ( IL-6, IL-8, TNF-α and MCP-1). Such co-cultures are thus a valuable tool to investigate the inflammatory response following exposure to nanoparticles. On the other hand, the cell membrane receptor CD14 (expressed only by macrophages) was used as an identification tool to distinguish each cell population in co-culture.Biodegradable nanoparticles having size around 230 nm, were prepared according to an emulsion-evaporation process using poly(lactide-co-glycolide) (PLGA). The use of polyvinylalcohol (PVA), chitosan (CS) or poloxamer (PF68) as stabilizers allows the formation of, respectively, neutral, positively- or negatively-charged nanoparticles. In addition, stabilizer-free nanoparticles (negatively charged) were prepared. Commercial titanium dioxide and polystyrene nanoparticles were used as non-biodegradable nanoparticles.After exposure to nanoparticles, uptake kinetics (flow cytometry and confocal microscopy) were performed in cells in mono and co-culture. Negatively-charged nanoparticles (stabilizer-free PLGA and PLGA/PF68 nanoparticles) were found in higher quantity in each cell population. Several cytotoxicity tests (MTT, trypan blue, selective membrane permeability, lactate dehydrogenase (LDH) release) have shown a low to medium cytotoxicity of PLGA nanoparticles. The cytotoxicity of PLGA/CS nanoparticles was attributed to the cytotoxicity of the chitosan in solution, whereas the cytotoxicity of PLGA/PF68 nanoparticles was attributed to their higher uptake. After 24 h exposure to a low dose of PLGA nanoparticles, a low inflammatory response was detected. Non-biodegradable nanoparticles have shown a slightly higher toxicity.Differences observed among PLGA nanoparticles in terms of cytotoxicity, cell uptake quantity and inflammatory response highlight the importance of the coating of nanocarriers for drug delivery application.

Le sepsis sévère est un problème majeur de santé publique mondiale. Sa mortalité élevée résulte d’une réponse dérégulée de l’hôte au sepsis, associant hyper inflammation et immunodépression. Le choc septique est la forme la plus grave du sepsis, impliquant une défaillance cardiovasculaire à laquelle peuvent se surajouter d’autres défaillances d’organes. Le foie, organe majeur impliqué dans la défense et la réponse au stress induit par la septicémie peut être victime de cette réponse inflammatoire exagérée. Une dysfonction hépatocellulaire (DHC) peut survenir et évoluer jusqu’à la défaillance d’organe. Dans ce cas, l’existence d’une insuffisance hépatique est associée à un mauvais pronostic dans le choc septique à court terme. A partir d’une grande cohorte prospective de patients en choc septique, nous avons montré dans ce travail que cette DHC était associée à une surmortalité à long terme. Malgré, une meilleure connaissance de la physiopathologie du sepsis et en particulier des altérations du foie, l’impact des thérapeutiques utilisées au cours du choc septique, telles que les catécholamines (adrénaline, noradrénaline), reste indéterminé. Les travaux préliminaires de notre équipe avaient permis de montrer l’effet pro-inflammatoire de l’adrénaline sur un modèle de culture hépatocytaire. Dans ce travail, nous avons cherché à évaluer l’influence des cellules de Küpffer acteur de l’environnement péri-hépatocytaire. Pour cela nous avons utilisé un modèle de co-culture d’hépatocytes (HepaRG) et de macrophages (THP1 différenciés par PMA), stimulé par le lipopolysaccharide (LPS) et/ou l’adrénaline. L’analyse de la réponse d’expression génique et de production de cytokines a permis d’identifier l’adrénaline comme facteur capable de modifier la réponse immune vers un état pro-inflammatoire même en présence d’un mécanisme anti-inflammatoire développé par les macrophages, indiquant ainsi un rôle potentiellement délétère de l’adrénaline sur les mécanismes de défenses du foie. / Severe sepsis is a major health problem. Its high mortality rate over the world is the result of a dysregulated host response to sepsis including an exaggerated inflammation response and immune suppression. Septic shock is the most severe expression of sepsis, including cardiovascular failure and other organ failure. The liver, a major organ involved in the defense and stress response induced by sepsis may also be a victim of this inflammatory response to infection. A hepatocellular dysfunction (HCD) can develop and evolve to the organ failure. In this case, the liver failure is associated with poor prognosis in septic shock in the early course of sepsis. Here, we have shown in a large prospective cohort of patients with septic shock that the HCD was associated with long-term mortality. Despite a better understanding of the pathophysiology of sepsis, especially liver changes, the impact of treatment used during septic shock, such as catecholamines (epinephrine, norepinephrine), remains unknown. The preliminary work of our team had demonstrated the proinflammatory effect of adrenaline on a hepatocyte culture model. In this work, we studied the influence of hepatocyte environment especially Küpffer cells. Thus, we used a co-culture model including hepatocytes (HepaRG) and macrophages (differentiated THP1 PMA) stimulated by lipopolysaccharide (LPS) and / or adrenaline. The gene expression and the cytokine profile analysis allowed to identify adrenaline as a factor able to shift the immune response to a proinflammatory state even if macrophages developed an anti-inflammatory response, indicating a deleterious effect of adrenaline on liver defense mechanisms.

La fibrose kystique (FK) est une maladie génétique autosomale récessive conduisant à une défaillance pulmonaire mortelle. Celle-ci est causée par l’expression dysfonctionnelle de l’allèle CFTR codant pour une protéine transmembranaire impliquée dans le transport Cl- des cellules de l’épithélium pulmonaire vers la lumière des voies respiratoires. Cette mutation induit la production d’un mucus visqueux qui entrave les voies respiratoires et favorise l’accumulation de bactéries pathogènes. L’éradication de cette présence bactérienne est maintenant l’enjeu primordial chez les patients FK afin de procurer un bien-être et de prolonger l’espérance de vie de ceux-ci. Le cheval de bataille de cette lutte au mieux-être du patient FK s’appuie en partie sur l’efficacité des antibiotiques. Cependant, nous nous heurtons à la capacité d’adaptation des bactéries face à l’antibiothérapie, ce qui nous conduit à développer sans cesse de nouvelles molécules thérapeutiques. Ainsi, l’essence de ce projet de recherche a été de caractériser l’efficacité de la tomatidine (TO); l’aglycone de la tomatine (un glycoalcaloïde), produit par les plants de tomate et de son analogue : la molécule FC04-100. Par le passé, notre laboratoire a établi que la TO possède une action antibactérienne contre Staphylococcus aureus prototype via l’inhibition de l’expression des facteurs de virulences associés au système de régulation ARG ainsi qu’en agissant comme potentialisateur d’action des aminoglycosides (AMI). De plus, la TO est également un inhibiteur de la réplication intracellulaire de S. aureus small-colony variant (SCV) infectant des cellules épithéliales pulmonaires différenciées (Calu-3). Le premier volet de mon projet a été consacré à l’évaluation du potentiel d’action de la TO contre S. aureus et Pseudomonas aeruginosa; deux bactéries fréquemment co-isolées des poumons des patients. Ainsi, lors de cette étude, j’ai démontré pour la première fois que la TO peut être employée seule contre S. aureus en tant qu’agent bactéricide lorsque celle-ci est utilisée en présence de P. aeruginosa. Ce phénomène dépend de la production par P. aeruginosa, du 2-heptyl-4-quinolone-N-oxide (HQNO) de l’endopeptidase LasA. De plus, j’ai évalué la possibilité d’utiliser un AMI et TO lorsque S. aureus et P. aeruginosa sont en co-culture afin de réduire la population bactérienne de ces deux pathogènes. Les résultats obtenus ont permis de démontrer qu’une combinaison, de tobramycine (TOB) et TO, permet d’inhiber significativement la croissance bactérienne d’un S. aureus résistant à la méthiciline (MRSA) résistant à la TOB et P. aeruginosa, co-cultivés en condition planctonique. Le deuxième volet de ma maîtrise visait à mesurer l’efficacité antibactérienne de FC04-100 en collaboration avec ma collègue Isabelle Guay. Pour ce projet, j’ai démontré l’efficacité de la combinaison FC04-100 et la gentamicine (GEN) contre un biofilm de S. aureus. Pour ce faire, j’ai utilisé une méthode de culture en microplaque 96 puits, permettant ainsi de former plusieurs bioflims et de tester plusieurs concentrations d’antibiotiques. Les résultats suite à l’exposition des biofilms à la combinaison TO-GEN ont démontré qu’il était possible de réduire significativement la viabilité bactérienne de S. aureus en biofilm. De plus, j’ai comparé l’efficacité de FC04-100 à TO dans un essai d’infection de cellules Calu-3 différenciées et infectées par une souche clinique de S. aureus SCV. Les résultats révèlent que ces deux composés diminuent significativement la viabilité bactérienne, et ce, en proportion similaire par rapport aux cellules infectées non traitées. L’ensemble des résultats obtenus dans ces deux projets a permis de démontrer clairement le potentiel antimicrobien de la TO et de son analogue FC04-100. Cette découverte apporte donc un nouveau squelette de molécule qui pourrait s’avérer utilisable comme antibiotique.

Cystic Fibrosis (CF) is the most common hereditary genetic disorder among Caucasians. Pseudomonas aeruginosa is a major cause of morbidity in cystic fibrosis patients. Chronic infection with P. aeruginosa eventually occurs and is associated with a switch to biofilm formation of the bacteria. The symptoms and pathology of acute and chronic P. aeruginosa infections differ greatly. The first line of defense within the lung is the physical barrier of the lung epithelia. The examination of established biofilm interactions with lung epithelia is difficult. Here, I use the Calgary Biofilm Device co-culture system to conduct the concurrent analysis of established biofilms and planktonic bacteria with A549 lung cells. Comparison of P. aeruginosa biofilm and planktonic bacteria’s effects on A549 lung cells showed that planktonic bacteria caused more A549 cell rounding and death, while biofilm stimulated more IL-8 release by epithelial cells. Biofilm was shown to secrete significantly more Pseudomonal Elastase than planktonic, causing A549 morphological changes and loss of tight junctions. The antimicrobial peptide LL-37 was shown to differentially affect biofilm and planktonic bacteria. LL-37 caused a decrease in twitching of planktonic bacteria and exposure to LL-37 for 48 hours resulted in a decrease in elastase secretion likely due to down-regulated type 2 secretion. When established biofilms were compared with newly adherent biofilms, young biofilms were shown to have characteristics similar to both planktonic bacteria and mature biofilms. From this data we can follow the pattern of bacterial virulence as P. aeruginosa transitions from the planktonic mode of growth to the eventual mature biofilm that is associated with chronic infection. In conclusion, this study provides the foundation for a co-culture system that can be used to study the host-pathogen interactions of mammalian epithelia with established P. aeruginosa biofilms. The future adaptations of this model will better represent the in vivo characteristics of chronic lung infection to delineate ongoing virulence mechanisms of the bacteria causing host cell stimulation and damage. / May 2016

L. monocytogenes is ubiquitous in environment and can grow and survive in a wide range of environmental conditions. It contaminates foods via raw materials or food processing environments. However, the current knowledge of its ecology and in particular, the mode of environmental survival and transmission of L. monocytogenes remains limited. One important aspect of environmental survival of L. monocytogenes may be contact with other microorganisms, including amoebae, which naturally feed on bacteria as a source of nutrients. In this context, research has shown that several intra-cellular pathogens are able to survive or replicate within free-living amoebae. In view of the potential for amoebae to act as environmental reservoirs for bacteria, the interaction of L. monocytogenes with freeliving Acanthamoeba spp. and the impact of plasmid-associated genes on their interaction were investigated. Several strains of environmental and clinical isolates of L. monocytogenes were used for co-culture with amoebae. Axenic amoebae were isolated from environmental sources (water, soil) by cultivation in PYG supplemented with antibiotics. L. monocytogenes strains were co-cultured with amoebae on plates, in trays (as monolayers of amoeba cells) and in flasks to provide qualitative and quantitative assessments of the survival of bacteria and amoebae. Bacteriological methods and microscopy (fluorescence, TEM and phase contrast) were used to track the fate of internalized bacteria. A vector that allowed GFP expression under control of the prfA promoter was used to assess the expression of Listeria virulence genes within amoeba cells. The role plasmid encoded genes in interactions of L. monocytogenes with amoebae was assessed using plasmid-cured versus wild type in the co-cultures. Finally the mechanisms of bacterial uptake and killing by A. polyphaga were assessed using chemical inhibitors that affected actin polymerization (Cytochalasin D, Wortmannin), phagosome-lysosome fusion (Suramin) and phagosomal acidification (ammonium chloride, Bafilomycin A and Monensin). Sequence analysis of a section of the large plasmid from strain DRDC8 revealed a high level of similarity of gene organization and DNA sequences with plasmid-borne genes found in other Listeria spp. and Gram-positive bacteria. While the majority of environmental isolates of L. monocytogenes contained a large plasmid, it was absent in clinical isolates. Further, plasmid of DRDC8 was lost during serial passage in HeLa cells. This data indicated that the plasmid may be readily lost during isolation procedures or during growth within host animals/cells and thus plasmid instability may explain the absence of plasmid in clinical isolates. Co-culture of L. monocytogenes with Acanthamoeba spp. showed these amoebae are able to actively phagocytose and kill bacteria within 2-5 h irrespective of temperature used. Amoebae killed both plasmid cured and LLO mutants with the same rate for the parental bacteria. Fluorescence microscopy and TEM of bacteria within trophozoites showed the bacteria become confined within tight vacuolar structures surrounded by lysosomes and mitochondria and degraded after 4 to 5 h post phagocytosis. This data indicated that although L. monocytogenes is an effective pathogen of mammalian cells, it could not escape from phagosomes and evade the killing mechanisms of amoeba trophozoites. Consequently, bacteria are killed within phagolysosome in trophozoites before they express their virulence genes to escape from phagosomes and get access to cytoplasm. This was confirmed by observing no GFP expression by bacteria carried prfA::gfp construct in co-culture with amoebae whereas it was observed during co-culture with HeLa cells. Using inhibitors, the mechanisms involved in phagocytosis, and killing of L. monocytogenes cells by A. polyphaga were assessed. The results showed that the uptake of bacterial cells is mediated by the trophozoites but not the bacteria and mannose binding protein is not involved in this process. Furthermore, pre-treatment of trophozoites with inhibitors indicated both phagosomal acidification and phagosome lysosome fusion are involved in killing of bacteria. These results suggest that compared to mammalian cells e.g. HeLa cells, amoeba trophozoites are better able to effectively inactivate and destroy internalized L. monocytogenes cells. In conclusion, Acanthamoeba spp. are able to uptake and kill L. monocytogenes cells in phagolysosome compartments. However, bacteria can saprophyticaly grow on materials released from amoeba trophozoites. Thus this group of amoebae is not able to harbour L. monocytogenes cells, or act as environmental reservoirs for this opportunistic pathogen under the laboratory conditions tested. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1292868 / Thesis (Ph.D.) -- University of Adelaide, School of Molecular and Biomedical Science, 2007