A Piscirickettsia salmonis-like bacterium associated with mortality of white seabass Atractoscion nobilis

摘要: Mortality among hatchery-reared juvenile white seabass Atractoscion nobilis in southern California, USA, was associated with infections by a Piscirickettsia salmonis-like organism (WSPSLO). Infected fish had no consistent external signs other than pale gills, lethargy and impaired swimming behavior. Internally, the kidney spleen were enlarged, some livers multiple foci. Smears from infected kidney, liver, stained Wright-Giemsa intracytoplasmic coccoid organisms, often pairs, that ranged size 0.5 to 1.0 microm. Microscopic lesions included multifocal hepatic, renal, splenic necrosis, intralesional macrophages contained WSPSLO. The bacterium isolated on cell lines of salmonid (CHSE-214) (WSBK) origin. WSPSLO induced plaque formation destroyed monolayers within 10 14 d incubation at temperatures 15 20 degrees C. retained infectivity for up 4 13 C, 7 but it inactivated 37 56 C 24 1 h, respectively. Freezing -20 reduced 100-fold. Dehydration resuspension distilled water completely bacterium. In contrast, nearly all its CHSE-214 cells following 72 h period seawater Polyclonal rabbit antibodies made reacted specifically indirect fluorescent antibody tests (IFAT) cultures smears tissues. Tissue salmon or P. salmonis weakly anti-WSPSLO serum. Conversely, polyclonal anti-P. serum produced positive reaction cells. as propagated highly virulent coho Oncorhynchus kisutch, inducing 80% mortality intraperitoneal injection 10(2.5)-50% tissue culture infectious doses per fish. We conclude possesses antigenic differences yet virulence equal known strains salmonis.