Genetic variation amongFlavobacterium psychrophilumisolates from wild and farmed salmonids in Norway and Chile

Abstract

Aims: To aim of the study was to describe the genetic relationship between isolates of Flavobacterium psychrophilum with a main emphasis of samples from Chile and Norway. The isolates have been obtained from farmed salmonids in Norway and Chile, and from wild salmonids in Norway, but isolates from North America and European countries are also included in the analysis. Methods and Results:The study is based on phylogenetic analysis of 16S rRNA and seven housekeeping genes (HG), gyrB, atpA, dnaK, trpB, fumC, murG and tuf, and the use of a multilocus sequence typing (MLST) system, based on nucleotide polymorphism in the HG, as an alternative to the phylogenies. The variation within the selected genes was limited, and the phylogenetic analysis gave little resolution between the isolates. The MLST gave a much better resolution resulting in 53 sequence types where the same sequences types could be found in Chile, North America and European countries, and in different host species. Conclusions: Multilocus sequence typing give a relatively good separation of different isolates of Fl. psychrophilum and show that there are no distinct geographical or host-specific isolates in the studied material from Chile, North America and Europe. Nor was it possible to separate between isolates from ulcers and systemic infections vs isolates from the surface of healthy salmonids. Significance and Impact of the Study: This study shows a wide geographical distribution of Fl. psychrophilum, indicating that the bacterium has a large potential for transmission over long distances, and between different salmonid hosts species. This knowledge will be important for future management of salmonids diseases connected to Fl. psychrophilum.

Variable Number of Tandem Repeats (VNTR) analysis of Flavobacterium psychrophilum from salmonids in Chile and Norway

“…The present study shows the same separation between F. psychrophilum isolates from Norway and Chile, as that documented in the previous MLST work [ 36 ]. The VNTR method used confirmed also the high diversity of the Chilean isolates shown by MLST, and other work by Avendaño et al [ 37 ] including a large number of isolates.…”

“…a MLVA system . The method gave, to a large extent, the same resolution as that found in a previous MLST study Apablaza et al [ 36 ], with a high diversity among Chilean isolates and less variation among the Norwegian isolates. The method was not able to separate isolates with respect to host species except for one cluster of distinct isolates from wild Atlantic salmon in Norway.…”

Multilocus Sequence Typing Identifies Epidemic Clones of Flavobacterium psychrophilum in Nordic Countries

“…Our study shows that since first recognition of BCWD in the Nordic countries, most outbreaks in rainbow trout have been caused by a group of closely related strains belonging to CC-ST10 (Table 1). Unfortunately, the previous work regarding MLST of Norwegian and Chilean F. psychrophilum isolates by Apablaza et al (41) involved sequencing of shorter loci and did not allow assigning of comparable STs. However, CC-ST10 in the present investigation includes ST2, the predicted founder in French (35), Japanese (39), Swiss (42), and global (27) studies.…”

Flavobacteria Isolated from the Milt of Feral Chinook Salmon of the Great Lakes

“…Another possible explanation could be related to the particular strains of F. psychrophilum infecting Great Lakes Chinook Salmon. Indeed, both Madsen and Dalsgaard (2008) and Kumagai and Nawata (2011) found multiple genetically distinct groups of F. psychrophilum in the milt of multiple salmonid species, and recent studies have found that genetic differences among F. psychrophilum strains can be associated with differential virulence and host species predilections (Nicolas et al 2008;Siekoula-Nguedia et al 2012;Apablaza et al 2013;Fujiwara-Nagata et al 2013;Strepparava et al 2013;Avendaño-Herrera et al 2014).…”