Edward Francis is the most significant scientist in the field of tularemia research. F. tularensis is a gram negative, aerobic, ascporogenous, immobile bacteria that belongs to family Francisellaceae. F. tularensis is one of the most infectious bacteria that can cause deadly disease tularemia by inhalation of only 10-15 bacteria. It is considered that F. tularensis can be used as a biological weapon, which is why all research that includes F. tularensis must be conducted in BSL-3 laboratories. There are three subspecies of F. tularensis that can cause disease in humans: tularensis (type A), holartica (type B) and mediasiatica. F. novicida, F. philomoragia and F. hispaniensis can cause tularemia in immunocompromised people. On the other hand, F. noatunensis is known as a fish pathogen while recently discovered species adapted to the environment include F. piscidida, F. guangzhouensis, F. opportunistica, F. salina, F. uliginis, F. 37 frigiditurris and F. adeliensis. All subspecies F. tularensis are different in virulence, geographical origin, and ability of causing diseases in humans or in animals. Transmission and infection in humans and other mammals can occur by contact with infected animals and animal products, through contaminated food and water, by insect bites such as ticks and mosquitoes and by aerosol. Symptoms of tularemia and severity of infections depend on the virulence of the pathogen, the way the bacteria enters the body, and the immune system. F. tularensis subsp. holarctica LVS (Live Vaccine Strain) is live attenuated vaccine produced from holartic strains in the countries of the former Soviet Union. The use of the vaccine in the United States and its licensing has not been yet accomplished due to a lack of knowledge about mechanisms that can weaken the bacteria. Genes found within FPI (Francisella pathogenicity island) have shown an important role in intracellular survival and reproduction of Franciselle in mammalian cells. Therefore, the aim of this study was determining the role of the iglI, iglG and genes pdpC F. tularensis subsp. holarctica in intracellular reproduction of A. castellanii to explain the life cycle of the bacterium under enviromental conditions. In practical work were used bacterial strain F. tularensis LVS, mutants iglI, iglG, pdpC and amoeba A. castellanii. Bacterial growth in amoebae were followed during 3 days. Since the number of bacteria in amoeba cells are the same as in the wild strain, it is concluded that the iglI, iglG and pdpC genes have no role in intracellular reproduction of F. tularensis subsp. holarctica strain LVS in amoeba A. castellanii. We can conclude that the bacterium does not exhibit the same virulence factors in amoeba cells and mammalian cells.