A travers l'évolution, les agents pathogènes ont développé des stratégies leur permettant de survivre au sein de leur hôte en interférant avec la biogénèse des phagolysosomes. Comme C. burnetii vit dans un phagosome acide incapable de fusionner avec les lysosomes et que sa virulence est associée à l'expression de son LPS, nous avons étudié le rôle du LPS de C. burnetii dans le détournement de la conversion phagosomale. En effet, nous avons montré que C. burnetii virulent ainsi que son LPS se localisent dans des compartiments Lamp-1+ qui n'acquièrent pas la CathepsineD et Rab7 n'est pas recruté à leur surface. Contrairement au LPS du variant avirulent de C. burnetii, qui est localisé dans les lysosomes, le LPS de C. burnetii virulent (vLPS) n'induit pas l'activation de la MAPKinase p38, empêche le recrutement de Rab7 à la surface des compartiments en déstabilisant le complexe HOPS. Finalement, nous avons démontré que la bactérie virulente exprimant le vLPS détourne la conversion phagosomale pour survivre et pour se multiplier dans les macrophages en évitant l'activation de l'axe MAPK-p38/Vps41-HOPS. Nous avons également étudié les mécanismes permettant à Tropheryma whipplei, l'agent de la maladie de Whipple, de se répliquer dans les macrophages puisque les macrophages sont la cible in vivo de cette bactérie. Nous avons montré que T. whipplei bloque la conversion de son phagosome. / Through evolution, pathogens have developed strategies to survive within their host by interfering with the biogenesis of phagolysosomes. As it is known that C. burnetii lives in acidic phagosome which is unable to fuse with the lysosomes and that its virulence is associated with the expression of LPS, we studied the role of C. burnetii LPS in hijacking of phagosomal conversion. Indeed, we showed that the virulent C. burnetii and its LPS are located in Lamp-1+ compartments which do not acquire CathepsineD and Rab7 is not recruited to their surface. Contrary to LPS of avirulent C. burnetii, which is located in the lysosomes, the LPS of virulent C. burnetii (vLPS) does not induce activation of the p38 MAPKinase and it prevents the recruitment of Rab7 to the surface of compartments by destabilizing the HOPS complex. Finally, we demonstrated that virulent bacteria expressing virulent LPS hijack phagosomal conversion to survive and multiply in macrophages by preventing activation of p38-MAPK/Vps41HOPS axis. We also studied the mechanisms by which Tropheryma whipplei, the agent of Whipple's disease, replicates in macrophages, which are its target in vivo. We have shown that T. whipplei blocks the conversion of its phagosome. Indeed, after purification of phagosomes containing-T. whipplei, we observed by Western blot and confocal microscopy that T. whipplei survives in an immature phagosome with characteristics of both early and late phagosomes (presence of Rab5 and Rab7) making it unable to fuse with lysosomes. As the IL-16 is known to induce replication of T. whipplei, we studied the effect of this cytokine on the phagosome biogenesis of T. whipplei.