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

• Published in: Journal of Fish Diseases
• Main Authors: Rojas, M E, Galleguillos, M, Díaz, S, Machuca, A, Carbonero, A, Smith, P A
• Other Authors: Grant Fondecyt
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2013
• Subjects: Atlantic salmon
• Online Access: http://dx.doi.org/10.1111/jfd.12019; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fjfd.12019; https://onlinelibrary.wiley.com/doi/pdf/10.1111/jfd.12019

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 P iscirickettsia salmonis, were inoculated in Atlantic salmon, S almo salar L ., and in three continuous cell lines in an effort to determine the presence of secretion of extracellular products ( ECP s) 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 ECP s was different among the P . salmonis isolates tested. The isolate that evidenced the highest cytotoxicity in its ECP s 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 ECP s 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 ECP s and at least some of them are thermolabile exotoxins that probably play a role in the pathogenesis of piscirickettsiosis.