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Optimisation of External Factors for Growth of Francisella novicida Within Dictyostelium discoideum

Francisella tularensis is a gram-negative, highly infectious bacterium that causes the zoonotic disease tularemia. The bacterium is able to replicate in mammalian, amoebae and arthropod cells. The social amoeba Dictyostelium discoideum has been used as a model organism to study phagocytosis, cell differentiation, cytokinesis, cell motility and virulence factors for many bacterial pathogens, such as Legionella, Mycobacterium, Klebsiella, and Salmonella. The aim of this study was to determine the influence of different incubation temperature and infectious dose on the ability of F. novicida to invade, survive and replicate in D. discoideum. The amoeba cells were infected with a different multiplicity of infection (5, 10, 100) and incubated at different temperatures (22, 25, 27, 30, 37 °C). The number of intracellular and extracellular bacteria within D. discoideum, as well as cytotoxicity, was determined at 2, 4, 24, 48 and 72 hours after infection. Our results show that the optimal temperature for Francisella intracellular grow within amoeba was 30 °C with the MOI of 10. We can conclude that this MOI and temperature induced linear growth of bacteria in Dictyostelium with low cytotoxicity.

Francisella, Dictyostelium, temperature, MOI, cytotoxicity

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