The unraveling panoply of Francisella tularensis virulence attributes

Francisella tularensis is a highly infectious Gram-negative bacterium causing the zoonotic disease tularemia. This facultative intracellular pathogen multiplies in vivo mainly inside macrophages, but has the capacity to infect and survive in many other cell types, including other phagocytic and nonphagocytic cells. In vitro, F. tularensis escapes rapidly from the phagosomal compartment and replicates in the cytoplasm of infected cells. An impressive number of novel genes related to F. tularensis pathogenesis have been identified recently. However, the information on biological functions still remains limited to a few of them. In this review, we will try to provide a comprehensive overview of the bacterial attributes, currently known — or suspected — to participate in F. tularensis virulence and will highlight the future challenges in F. tularensis research.