Summary auto-generated
This study characterized Vibrio viscosus and Vibrio wodanis, psychrotropic bacteria associated with 'winter ulcer' disease in farmed salmonid fish in Scandinavia and Scotland. Researchers analyzed 68 fish isolates and 3 reference strains using biochemical tests, protein electrophoresis (SDS-PAGE), and DNA fingerprinting (AFLP). V. viscosus strains from diseased fish formed homogeneous subgroups correlating with geographical origin, with Norwegian and Icelandic isolates showing distinct patterns. V. wodanis strains demonstrated greater genetic and biochemical heterogeneity without clear geographical clustering. Sequencing of 16S rRNA genes revealed V. viscosus shared 99% sequence similarity with Moritella marina, placing it outside the Vibrio genus. V. wodanis showed 98.8% similarity to Vibrio logei. Virulence testing confirmed V. viscosus strains were pathogenic to Atlantic salmon, causing characteristic skin ulcers and internal hemorrhaging. Based on phylogenetic evidence, the authors proposed reclassifying V. viscosus as Moritella viscosa comb. nov., reflecting its true evolutionary relationship within the γ-proteobacteria.
Key findings
- V. viscosus shares 99% 16S rRNA sequence similarity to Moritella marina and should be reclassified as Moritella viscosa, not retained in genus Vibrio
- V. viscosus strains clustered by geographical origin (Iceland vs. Norway) using AFLP fingerprinting, suggesting clonal spread within and between farms
- V. wodanis strains showed greater genetic and phenotypic heterogeneity than V. viscosus and did not cluster by geography
- Challenge experiments confirmed V. viscosus strains were virulent to Atlantic salmon, producing characteristic winter ulcer lesions with skin necrosis and internal hemorrhaging
- V. viscosus is a psychrotroph restricted to 4-21°C growth, with specific salt tolerance requirements (2-3% NaCl) distinct from M. marina
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Abstract
Vibrio viscosus and Vibrio wodanis are recently described species of psychrotropic bacteria that have been found associated with a disease called 'winter ulcer', affecting salmonid fish reared in saline water in Norway, Iceland and recently in Scotland. V. viscosus and V. wodanis strains initially isolated from fish in Iceland and Norway were subjected to characterization using biochemical tests, SDS-PAGE of whole-cell proteins and a novel DNA fingerprinting method, amplified fragment length polymorphism (AFLP). The V. viscosus strains isolated from diseased fish grouped into homogeneous subgroups according to geographical origin and challenge experiments revealed that representatives of these groups are virulent. The results revealed that the V. wodanis strains are heterogeneous genotypically and phenotypically. Sequencing of almost complete 16S rRNA genes of V. viscosus and V. wodanis revealed that V. viscosus showed a 99.1% sequence similarity to Moritella marina and V. wodanis showed a 98.8% sequence similarity to Vibrio logei CIP 103204. A reclassification of Vibrio viscosus as Moritella viscosa comb. nov. is proposed.