Francisellaceae is a family of bacteria that are primarily known for their role as pathogens in various animal species. These bacteria are small, gram-negative, and often found in the blood of their hosts. They are particularly notable for their association with certain diseases in mammals, including Francisella tularensis, which causes tularemia in humans. Members of the Francisellaceae family are typically intracellular, meaning they can live and reproduce within the cells of their hosts. This ability allows them to evade the host's immune system, making infections difficult to treat. Research on these bacteria is important for understanding their biology and developing effective treatments for the diseases they cause.