FIG.2.

The role of free-living amoebae as a reservoir of intracellular bacteria, as a Trojan horse, in the transmission of its bacterial host, in the selection of virulence traits, and in the adaptation of the bacteria to macrophages. The bacteria are shown in red, the amoebae are shown in grey, and their mitochondria are shown in green. (Top) Life cycle of amoeba-resistant bacteria within amoebae present in the environment or in the nasal mucosa. (Bottom) Amoeba-resistant microorganisms in the lower respiratory tract. During the cycle of intra-amoebal replication, bacteria select virulence traits. Moreover, amoebal vacuoles represent an important reservoir of bacteria, which may reach alveolar macrophages within amoebae, within expelled vesicles, or free. The strategy of resistance to macrophage microbicidal effectors varies from species to species and might have been acquired following exposure to environmental predators such as free-living amoebae.