Abstract

Piscirickettsia salmonis is a Gram-negative bacterium and a facultative intracellular pathogen, etiological agent of “Salmon Rickettsial Syndrome (SRS)”, a disease that seriously affects the salmon farming in Chile. Although, the disease produce economic loses over US$700 million per year, do not exist efficient control and prophylactic strategies. The life cycle of P. salmonis has not be completely described, although the agent has been detected in native fishes, has not been identified reservoirs or vectors in the marine environment. Elucidate the life cycle of this pathogen is the key to develop new and efficient preventive and control strategies. Objectives: Determinate the capacity of P. salmonis to infect and survive in free-living protozoa, using Acanthamoeba castellanii as model. Methods: Was done an infection kinetics of 2, 24, 48 and 168 h in 712-PYG broth at 18ªC with a MOI of 10, using a P. salmonis EM-90. The infection was determined by immunofluorescence using epifluorescence and Confocal microscopes. Additionally, were evaluated the expression by qRT-PCR of P. salmonis virulence genes (Dot/Icm secretion system). Results: Our results confirm that P. salmonis is able to infect A. castellanii. The internalization was through phagocytosis and the bacteria remains inside digestives and contractile vacuoles at least for seven days, in both, trophozoite and cyst of the amoeba. The expression of dot/icm genes at earlier stages of infection confirm the viability of P. salmonis inside the amoeba and demonstrate an active infection. Finally, Our results suggest that P. salmonis could use marine amoeba as putative vector or reservoir in salmon farms.