Abstract
BackgroundThe study presents the phenotypic and genetic characterization of selected P. salmonis isolates from Atlantic salmon and rainbow trout suffering from SRS (salmonid rickettsial septicemia) in Chile and in Canada. The phenotypic characterization of the P. salmonis isolates were based on growth on different agar media (including a newly developed medium), different growth temperatures, antibiotics susceptibility and biochemical tests.ResultsThis is the first study differentiating Chilean P. salmonis isolates into two separate genetic groups. Genotyping, based on 16S rRNA-ITS and concatenated housekeeping genes grouped the selected isolates into two clades, constituted by the Chilean strains, while the Canadian isolates form a branch in the phylogenetic tree. The latter consisted of two isolates that were different in both genetic and phenotypic characteristics. The phylogenies and the MLST do not reflect the origin of the isolates with respect to host species. The isolates included were heterogeneous in phenotypic tests.ConclusionsThe genotyping methods developed in this study provided a tool for separation of P. salmonis isolates into distinct clades. The SRS outbreaks in Chile are caused by minimum two different genetic groups of P. salmonis. This heterogeneity should be considered in future development of vaccines against this bacterium in Chile. Two different strains of P. salmonis, in regards to genetic and phenotypic characteristics, can occur in the same contemporary outbreak of SRS.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-016-0681-0) contains supplementary material, which is available to authorized users.
Highlights
The study presents the phenotypic and genetic characterization of selected P. salmonis isolates from Atlantic salmon and rainbow trout suffering from salmonid rickettsial septicemia (SRS) in Chile and in Canada
Phenotypic characterization The colonies grown on SRS blood agar (SRS-blood agar (BA)) were slightly convex, grey-white, shiny, and centrally opaque with translucent, slightly undulating margins
The present study shows the 18 Chilean P. salmonis isolates as two genetically distinct groups, a separation supported by all three genotyping methods
Summary
The study presents the phenotypic and genetic characterization of selected P. salmonis isolates from Atlantic salmon and rainbow trout suffering from SRS (salmonid rickettsial septicemia) in Chile and in Canada. The Chilean aquaculture industry has constantly faced problems with Piscirickettsia salmonis, which causes salmonid rickettsial septicemia (SRS) [1]. This disease causes high mortalities in several salmonids species Atlantic salmon (Salmo salar), Rainbow trout (Onchorhyncus mykiss), Coho salmon (Onchorhyncus kisutch), and was responsible for 90 % of the total use of antibiotics in Chile in 2014 [2]. This lack of protection suggests that more basic knowledge is needed about the biology of P. salmonis
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