Evidence of exotoxin secretion of Piscirickettsia salmonis, the causative agent of piscirickettsiosis

Abstract

Piscirickettsia salmonis is the aetiological agent of piscirickettsiosis, a disease which affects a variety of teleost species and that is particularly severe in salmonid fish. Bacterial-free supernatants, obtained from cultures of three isolates of Piscirickettsia salmonis, were inoculated in Atlantic salmon, Salmo salar L., and in three continuous cell lines in an effort to determine the presence of secretion of extracellular products (ECPs) by this microorganism. Although steatosis was found in some liver samples, no mortalities or clinical signs occurred in the inoculated fish. Clear cytotoxicity was observed after inoculation in the cell lines CHSE-214 and ASK, derived from salmonid tissues, but not in MDBK, which is of mammalian origin. The degree of cytotoxicity of the ECPs was different among the P. salmonis isolates tested. The isolate that evidenced the highest cytotoxicity in its ECPs exhibited only an intermediate virulence level after challenging fish with bacterial suspensions of the three P. salmonis isolates. Almost complete inhibition of the cytotoxic activity of ECPs was seen after proteinase K treatment, indicating their peptidic nature, and a total preclusion of the cytotoxicity was shown after their incubation at 50 °C for 30 min. Results show that P. salmonis can produce ECPs and at least some of them are thermolabile exotoxins that probably play a role in the pathogenesis of piscirickettsiosis.

Transcriptome Analysis of the Intracellular Facultative Pathogen Piscirickettsia salmonis: Expression of Putative Groups of Genes Associated with Virulence and Iron Metabolism

“…Additionally, P . salmonis can produce extracellular products (EPCs), at least some of which are thermo-labile exotoxins that probably play a role in the pathogenesis of Piscirickettsiosis [35]. Overall, the results showed that P .…”

“…Furthermore, the expressed genes related to flagellar structure could play a similar role to a type III secretion system during pathogenic processes, supporting the production of extracellular products by P . salmonis [35], but still this require further analysis considering the interaction with the host.…”

Addressing viral and bacterial threats to salmon farming in Chile: historical contexts and perspectives for management and control

“…Gene expressions related to flagella structures have been reported in P. salmonis (Rojas et al . ; Carril et al . ), and a relationship between biofilm formation and genes related to chemotaxis has been suggested (Albornoz et al .…”

Effect of Piscirickettsia salmonis inoculation on the ASK continuous cell line

“…Since then, this condition has been detected in a variety of teleost fish from distant geographical regions in the world, but so far it has been consistently more severe in salmonid species reared in the South Pacific Ocean in Chile ( Arkush & Bartholomew ; Rojas et al . ).…”

“…), and these cells were since then the most extensively used substrate for this bacterium propagation (Arkush & Bartholomew ; Rojas et al . ). For some years, it was thought that P. salmonis could replicate in vitro only in cell cultures, but rather recently, it was found that it can also be grown in some enriched artificial media (Mauel, Ware & Smith ; Mikalsen et al .…”