IN-VITRO INFECTION OF A CELL-LINE FROM ICTALURUS-NEBULOSUS WITH PISCIRICKETTSIA-SALMONIS

Piscirickettsia salmonis, the etiologic agent of salmonid rickettsial septicemia (SRS), affects several species of salmonids. Previous repor ts using the appearance of cytopathic effect (CPE) as the criterion fo r susceptibility, showed that Piscirickettsia salmonis (ATCC strain) c an be grown in vitro in some cells lines derived from salmonid fish, b ut not in BE cells from brown bullhead (Ictalurus nebulosus) and BF-2 cells from bluegill (Lepomis macrocthirus). In this study we describe growth of P. salmonis (ATCC strain VR 1361) in a cell line previously believed to be nonpermissive for this organism. CPE was first detected in chinook salmon embryo (CHSE-214) and epithelioma papulosum ciprini (EPC) cell fines at 6 d postinfection (dpi). In contrast, using BE ce ll line, CPE was first detected 45 dpi and the monolayer completed CPE by 78 dpi. Electron microscopic examination of BE cells 78 dpi reveal ed free, intracytoplasmic and extracellular localization of the agent. P. salmonis was also observed within membrane-bounded vacuoles in BB cells, similar to that described in CHSE 214 cells. Contrary to earlie r reports, results from the present study show that the BB cell line, is susceptible to Piscirickettsia salmonis infection, The delayed onse t of CPE in BB cells in comparison to other permissive cell lines sugg ests that BB cells are not ideal hosts for P. salmonis. Interestingly, however, these results demonstrate that P. salmonis can infect non-sa lmonid cell lines, and raises the possibility that nonsalmonid fish ma y play a role in the persistence and transmission of SRS in the natura l environment.