Abstract
The amoeba Dictyostelium discoideum has been used as a model organism to study host-pathogen interaction in many intracellular bacteria. Francisella tularensis is a Gram-negative, highly infectious bacterium that causes the zoonotic disease tularemia. The bacterium is able to replicate in different phagocytic and nonphagocytic cells including mammalian, amoebae, and arthropod cells. The aim of this study was to determine the optimal temperature and infection dose in the interaction of Francisella novicida with D. discoideum in order to establish a model of Francisella infection in the social amoeba. The amoeba cells were infected with a different multiplicity of infection (5, 10, and 100) and incubated at different temperatures (22, 25, 27, 30, and 37°C). The number of intracellular bacteria within D. discoideum, as well as cytotoxicity, was determined at 2, 4, 24, 48, and 72 hours after infection. Our results showed that the optimal temperature for Francisella intracellular replication within amoeba is 30°C with the MOI of 10. We can conclude that this MOI and temperature induced the optimal growth of bacteria in Dictyostelium with low cytotoxicity.
Highlights
Francisella tularensis is a small Gram-negative bacterium that causes the zoonotic disease tularemia
We examined the role of various incubation temperatures and the dose of infection on F. novicida capability to survive and replicate within D. discoideum
Prolonged Survival of Bacteria In Vitro Is Temperature Dependent. e effect of different incubation temperatures on the survival of F. novicida in vitro was examined. e bacterial suspensions were incubated at temperatures of log10 (CFU/ml) log10 (CFU/ml)
Summary
Francisella tularensis is a small Gram-negative bacterium that causes the zoonotic disease tularemia. Ere are three subspecies of F. tularensis that cause human illness: tularensis (Type A), holartica (Type B), and mediasiatica [3]. F. novicida, F. philomiragia, and F. hispaniensis can cause tularemia in immunocompromised people [4]. F. noatunensis has been recognized as a fish pathogen, while recently new environmentally adapted species have been discovered including F. piscidida, F. guangzhouensis, F. opportunistica, F. Francisella is known as a fastidious organism with many growth requirements in vitro. E bacterium is difficult to culture and grows slowly at 37°C, requiring enriched growth medium [8]. Each species of the genus Francisella require different growth and medium conditions. Francisella requires medium supplemented with cysteine for cultivation
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