The infection process of Piscirickettsia salmonis in fish macrophages is dependent upon interaction with host-cell clathrin and actin.

Piscirickettsia salmonis is an aggressive fish pathogen that causes Piscirickettsiosis, a systemic disease that threatens the sustainability of salmon production in Chile. To date, the infection strategies of this bacterium are poorly characterized, a Dot/Icm Type IV Secretion System homolog for intracellular multiplication and survival in macrophages is suggested. Since an invading pathogen and its host develop a complex interaction in which the pathogen strives to survive and replicate, while the host tries to eliminate infected cells and the invading pathogen, we decided to evaluate how the bacterium enters macrophages, its preferred target in vivo, and to follow its fate while struggling with its host using actin cytoskeleton as a molecular marker. We were able to demonstrate that clathrin is required for internalization and that actin cytoskeleton plays a demonstrative role throughout the infective process. Indeed, unlike other fish pathogens, P. salmonis fully exploits the actin monomers both from the disorganized cytoskeleton and an apparently pathogen-induced de novo synthesis of actin, generating tridimensional vacuoles that are increasingly detected at later stages of infection. We expect our results to contribute to a better understanding of the pathogenesis of this important fish pathogen.