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Characterization of spaC-type Erysipelothrix sp. isolates causing systemic disease in ornamental fish.
E K Pomaranski1, S R Reichley2, R Yanong3
1Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, Davis, CA, USA.
Journal of Fish Diseases
|July 15, 2017
Summary
Ornamental fish are experiencing mortality from a novel Erysipelothrix sp. bacterium. Genetic analysis reveals these fish pathogens are distinct from other Erysipelothrix species.
Area of Science:
- Aquatic microbiology
- Fish pathology
- Bacterial genomics
Background:
- Erysipelothrix sp. infections have caused low-to-moderate mortality in ornamental fish since 2012.
- Histological findings include facial cellulitis, necrotizing dermatitis, myositis, and disseminated coelomitis with Gram-positive bacteria.
Purpose of the Study:
- To phenotypically and genetically characterize Erysipelothrix sp. isolates from diseased ornamental fish.
- To compare these isolates with known Erysipelothrix rhusiopathiae and Erysipelothrix tonsillarum strains.
Main Methods:
- Phenotypic identification of 16 Erysipelothrix sp. isolates from diseased cyprinid and characid fish.
- Intracoelomic challenge of zebrafish (Danio rerio) with ornamental fish isolates.
- Comparative phenotypic and genetic analysis (PCR for spaC, gyrB sequencing, rep-PCR) against reference strains.
Main Results:
- Ornamental fish isolates were phenotypically identified as E. rhusiopathiae.
- Zebrafish challenged with isolates showed similar clinical and histological signs.
- Fish isolates were largely clonal and genetically distinct from other Erysipelothrix spp. (<92% gyrB similarity, <60% rep-PCR similarity).
- All fish isolates were PCR positive for spaC.
Conclusions:
- Erysipelothrix isolates from diseased ornamental fish exhibit significant genetic divergence from known Erysipelothrix species.
- These findings suggest the ornamental fish isolates may represent a genetically distinct species.
- The genetic variability of Erysipelothrix spa types is further supported.
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