Legionella pneumophila is a gram-negative aerobic bacteria which belong to the family Legionelaceae. Legionella is ubiquitous in the nature, and is particularly widespread in the aquatic environment. The ability to survive in protozoa allows the bacterium to survive in unfavorable conditions. L. pneumophila causes a milder form of febrile disease, pontiac fever and severe form of the disease, atypical pneumonia, which is called legionnaires' disease. Francisella tularensis is a gram-negative bacteria which belongs to the family Franciselaceae. The family Franciselaceae contains only genus Francisella which includes the following subspecies: F. tularensis, F. hispaniensis, F. philomiragia, F. noatunensis and F. novicida.F. tularensis is divided into three subspecies of F. tularensis subsp. tularensis (type A), F. tularensis subsp. holarctica (type B) and F. tularensis subsp. mediastatica. F. tularensis subsp. tularensis (type A) and F. tularensis subsp. holarctica (type B) cause disease in humans, while F. tularensis subsp. mediastatica showed to be less virulent. F. tularensis subsp. tularensis is avery virulent bacterium, and because of a very low infection dose and airbone transmission, is considered a potential biological weapon.Until recently, the fourth subspecies considered novicida, but it is still classified as a separate species. F. novicida is the avirulent bacteria that causes disease only in immunocompromised. The aim of this study was to monitor the entry and growth of bacteria F. novicida and L. pneumophila in Dictyostelium discoideum cells after treatment with cytochalasin D. Also, we wanted to determine whether the concentration of cytochalasin D has an influence on number of intracellular bacteria. Cytochalasin D, an alkaloid fungi depolymerize actin filaments in a way that it binds to one end and thereby blocks its further growth and thus is referred to as a polymerization inhibitor of actin filaments. The kinetics of growth and reproduction of bacteria L. pneumophila and F. novicida in amoeba D. discoideum treated with cytochalasin D is followed by a period of 1, 5, 24 and 48 hours after infection. Number of intracellular bacteria was determined by seeding tenfold dilutions on BCYE surface.Our results show that the bacteria F. novicida and L. pneumophila successfully survive and replicate in amoeba D. discoideum. The number of bacteria F. novicida within the amoeba reaches maximum in the period of 48 hours after infection. However, the results showed that the addition of cytochalasin D, as well as its concentration, has no impact on the growth of F. novicida and L. pneumophila in amoeba D. discoideum.