Listeria monocytogenes (L. monocytogenes) are Gram-positive, facultatively anaerobic and intracellular bacilli, occupying a wide range of ecological niches and are responsible for a number of serious infections in man. Primarily transmitted to humans through contaminated food stocks, L. monocytogenes invade mammalian cells in a phagosome, escaping and growing in the cell cytoplasm. Currently, there is a great deal of information about pathogenesis of L. monocytogenes, however, much less is known about the physiology of the bacteria. In particular, very little is known about the physiology during intracellular growth and even less about host cell physiology and changes in response to infection. The focus of this research was to address these issues using a multidisciplinary approach, utilising multiple biological techniques. The catabolic metabolism of L.monocytogenes was elucidated using mutagenesis and protein purification studies. The results are not completely conclusive; however, it was shown that unlike in Escherichia coli, L.moncytogenes may not be dependent on fermentation enzymes Ldh and Pflb during anaerobic growth. Instead anaerobic respiration is hypothesised, utilising a putative fumarate reductase with fumarate as a terminal electron acceptor. The putative fumarate reductase gene was purified and confirmed to have enzymatic activity.External and internal metabolism of HeLa cells, and the effect of L.monocytogenes infection was elucidated by mass spectrometry. The external metabolomic studies proved inconclusive. The internal metabolomic studies show that a number of key amino acids are being sequestered by L.monocytogenes during the course of an infection. Also, the studies show that a large number of carbon compounds are being sequestered by L.monocytogenes, pointing to a complex carbon metabolism for L.monocytogenes during intracellular growth. A targeted analysis of the nitrogen metabolism of L.monocytogenes has shown that L.monocytogenes may utilise a number of nitrogen compounds with glutamine and glutamate being particularly important. The ability to synthesise glutamine de novo is shown to be essential for normal intracellular growth.

Les molécules du Complexe Majeur d'Histocompatibilité de classe I (CMH I) contrôlent la plasticité synaptique dans le système nerveux central (SNC) et plusieurs travaux expérimentaux suggèrent des interactions antigène-dépendantes entre des neurones infectés par des virus et les lymphocytes T CD8. Cependant, le rôle de la présentation des antigènes par le CMH I des neurones sur la physiopathologie de l'infection par Toxoplasma gondii (T. gondii) n'a pas encore été clarifié. Après la dissémination aigue sous forme de tachyzoites, T. gondii se convertit en bradyzoites, forme persistante dans les neurones du SNC. Chez les individus immunocompétents, la toxoplasmose latente est associée à des variations des fonctions cognitives ainsi qu'à des pathologies neuropsychiatriques. Les sujets dont le système immunitaire est dysfonctionnel peuvent développer une encéphalite létale causée par T. gondii, qui est caractérisée par une réplication du parasite, une infiltration massive et des agrégats leucocytaires et l'activation des cellules gliales. Les lymphocytes T (LT) CD8 et le CMH I sont des facteurs-clés contrôlant la résistance à l'encéphalite. Utiliser les LT CD8 pour éliminer les kystes chez des sujets à risque est une piste thérapeutique intéressante en raison de l'absence d'approches pharmacologiques ciblant les bradyzoites. A ce jour, les mécanismes et la pertinence fonctionnelle de la présentation des antigènes dérivés de T. gondii par les neurones restent à déterminer, ainsi que la contribution des différents stades parasitaires au contrôle de l'infection. L'utilisation de nouveaux parasites exprimant un antigène immunodominant uniquement au stade tachyzoite a permis de montrer que la reconnaissance par les LT CD8 d'antigènes issus des tachyzoites est suffisante pour une protection efficace contre l'encéphalite.[...] / In the Central Nervous System (CNS), Major Histocompatibility Complex class I (MHC I) molecules regulate synaptic plasticity and evidence suggests antigen-specific interactions between virus-infected neurons and CD8 T cells. Yet, little is known about the impact of neuronal MHC I presentation on the pathophysiology of infection by the neurotropic Toxoplasma gondii (T. gondii) parasite. Following acute dissemination as tachyzoites, T. gondii converts into bradyzoites that persist inside cysts within neurons of the CNS. In immunocompetent hosts, latent toxoplasmosis is associated with cognitive changes and neuropsychiatric disorders. Hosts with sub-optimal immune responses may develop a lethal T. gondii Encephalitis (TE), characterized by parasite replication, granuloma-like structures with massive immune cell influx and glial cell activation. CD8 T cells and MHC I are key determinants of TE resistance. Harnessing CD8 T cells in at-risk individuals may turn helpful in the future as we are currently lacking an effective pharmacological approach to eradicate bradyzoites. Yet the mechanisms and functional relevance of neuronal MHC I presentation of T. gondii remain unexplored, as well as which stage of the parasite contributes to efficient control of the infection. Using new T. gondii parasites with restricted expression of the immunodominant antigen at the tachyzoite stage, this work showed that CD8 T cell recognition of tachyzoite antigens at early stages of brain invasion is enough to protect from TE. Interestingly, by comparing situations of toxoplasmosis with varying TE severity and by pioneering antigen presentation assays with T. gondii-infected primary neurons, we revealed that TE susceptibility may be underlied by sub-optimal MHC I presentation of tachyzoites antigens by neurons. At last, we describe a mouse model that allows conditional deletion of a MHC I allele that is essential for TE resistance (H-2Ld). [...]