Experimental vertical transmission of Piscirickettsia salmonis and in vitro study of attachment and mode of entrance into the fish ovum

Abstract

Piscirickettsia salmonis is a pathogenic bacterial agent causing septicaemic disease in salmon. Since its isolation in Chile in 1989, P. salmonis has continually produced high mortality rates in salmon farms. Little information exists regarding the mechanisms of vertical transmission of this pathogen. Experimental vertical transmission was established in the present study by inoculation of male and female rainbow trout broodstock with P. salmonis. The bacterium was subsequently detected using indirect immunofluorescence in milt and coelomic fluid of the majority of inoculated broodstock (14/15). Bacteria were detected in the fry when 1 or both parents were inoculated, although none of the infected fry presented signs of the disease. P. salmonis was also detected in progeny obtained through fertilisation ova from non-inoculated females incubated in a medium containing a bacterial suspension, demonstrating transmission during the process of fertilisation. Ova infected in vitro were examined at sample periods from 30 s to 60 min using scanning electron microscopy. This demonstrated that the bacterium attaches to the ova by means of membrane extensions, structures which we have called 'piscirickettsial attachment complex' (PAC) and which would allow later penetration into the ovum.

Immunization Strategies against Piscirickettsia salmonis Infections: Review of Vaccination Approaches and Modalities and Their Associated Immune Response Profiles

“…No vector or intermediate host has been identified (17), and during experimental trials, the pathogen has been observed in the milt and celomic fluid of adult brood fish, and also in fry of infected brood fish, suggesting that the bacterium is transmitted vertically (33). P. salmonis has also been reported from outbreaks in freshwater (1), but is primarily a pathogen that causes clinical disease in sea water.…”

Identification and genetic characterization of Piscirickettsia salmonis in native fish from southern Chile

“…Vertical transmission of the bacteria from progenitors to eggs has also been demonstrated in vitro and in vivo through the detection of bacteria in eggs experimentally infected with the bacteria taken from healthy females. Moreover, in trout infected by intraperitoneal injection of P. salmonis, the bacterium was detected in eggs and in coelomic and seminal fluids, and potential mechanisms for transmission have been proposed (Larenas et al 2003).…”

Draft Genome Sequence of the Fish Pathogen Piscirickettsia salmonis

“…Notable aspects to the P. salmonis genome sequence include the presence of type IV pilus genes, which may represent the appendages seen as the bacteria come into contact with fish cells (11), and bacteriophage genes that may represent the phage particles associated with P. salmonis (12). Type IV secretion system/conjugation genes are present in large clusters, which may be critical for intracellular survival and/or replication.…”