Abstract

Piscirickettsia salmonis is a facultative intracellular Gram-negative bacterium, known as the etiological agent of the salmonid rickettsial syndrome (SRS). It causes a systemic infection in salmonid fishes and it is one of the main agents responsible for the high mortality in farmed salmons. P. salmonis induces histological changes in salmon tissues, mainly in liver, kidney, spleen and intestine,[1] but the possible effect of this bacterium on lipid metabolism in salmon fishes is still unknown. Detection of this bacterium includes mainly, molecular biology techniques and immunohistochemistry. Recently, the use of mass spectrometry profiling technique to detect P. salmonis in serum samples has been also reported.[2] In the searching of new detection alternatives for this bacterium, the present study aims to evaluate the changes in lipid metabolism of salmonid liver due to the presence of P. salmonis and to compare lipid profiles in healthy and infected fishes using mass spectrometry techniques and statistical tools. Salmon liver samples were obtained from a controlled bioassay, where Atlantic salmon (Salmo salar) was challenged with P. salmonis in a cohabitation model. To test the hypothesis that liver lipid metabolism is altered in presence of P. salmonis, a comparison of the lipid profile in healthy and P. salmonis infected fishes were performed. The presence of the bacterium in salmon samples was checked by RT-PCR and histochemistry analysis . Lipids were extracted following the classical methodology reported by Folch et al. (1957)[3] with modifications. The obtained lipid extracts were analyzed by ESI-MS and MALDI-TOF-MS techniques. Liver lipid profiles showed differences between healthy and P. salmonis infected fishes. Those differences were corroborated through statistical analysis. The obtained results demonstrated that Atlantic salmon exhibits changes in its lipid metabolism in presence of P. salmonis and those changes can be detected by mass spectrometry techniques. The results exposed in this work indicate that the use of mass spectrometry techniques could be considered as an alternative to traditional methods to detect the presence of P. salmonis in salmon tissues.