Abstract

Piscirickettsiosis is a bacterial, septicaemic disease caused by the obligate intracellular bacterium Piscirickettsia salmonis that affects maricultured salmonid species. The LF-89 type strain has been reported to be a highly virulent strain. This work presents a comparison of the virulence and electrophoretic profile shown by two passages, 13th (P13) and 42nd (P42) of the LF-89 strain of P. salmonis cultured in the CHSE-214 cell line. Two groups of 20 coho salmon (Oncorhynchus kisutch) were inoculated with P13 and P42, respectively, both with 105.3 TCID50/mL of the bacterium. None of the fish challenged with P. salmonis P42 died, while those inoculated with P13 reached a cumulative mortality of 70% at 30 days post-inoculation. By SDS-PAGE, four peptide bands of molecular weights between 70 and 110 kDa were found in P42 but not in P13 of this bacterium. These results suggest that the pathogenic nature of a strain could be reflected in its electrophoretic pattern. It would be worthwhile to considere the changes in protein expression and associated virulence within strains of P. salmonis in the research aimed to develop vaccines and new diagnostic tests for this fish pathogen.