Experimental Lactococcus garvieae infection in zebrafish and first evidence of its ability to invade non-phagocytic cells

Zebrafish has been used for studying infections and host-pathogen interactions in different bacterial fish pathogens. In the present study we evaluated the ability of Lactococcus garvieae to infect zebrafish when inoculated intraperitoneally with 2 × 107 UFC of this pathogen. L. garvieae can colonize and invade zebrafish at multiple anatomical sites causing a lethal acute septicemic infection with clinical signs and lesions consistent with those observed in lactococcosis outbreaks. Immunohistochemical studies showed the presence of L. garvieae into macrophages as well as into non-phagocytic zebrafish cells of liver (hepatocytes). The internalization capacity showed by L. garvieae in zebrafish cells was confirmed in the rainbow trout cell line RTG-2. Our results provide the first evidence that L. garvieae is able to invade non-phagocytic host cells.