Description of Erysipelothrix piscisicarius sp. nov., an emergent fish pathogen, and assessment of virulence using a Tiger Barb (Puntigrus tetrazona) infection model

Authors: POMARANSKI, E. - University Of California, Davis; GRIFFIN, M. - Mississippi State University; CAMUS, A. - University Of Georgia; ARMWOOD, A. - University Of Georgia; SHELLEY, J - 5d Tropical Inc; Waldbieser, Geoffrey - Geoff; Lafrentz, Benjamin; Garcia, Julio; YANONG, ROY - University Of Florida; SOTO, E - University Of California, Davis

Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2019
Publication Date: 11/4/2019
Citation: Pomaranski, E.K., Griffin, M.J., Camus, A.C., Armwood, A.R., Shelley, J., Waldbieser, G.C., Lafrentz, B.R., Garcia, J.C., Yanong, R., Soto, E. 2019. Description of Erysipelothrix piscisicarius sp. nov., an emergent fish pathogen, and assessment of virulence using a Tiger Barb (Puntigrus tetrazona) infection model. International Journal of Systematic and Evolutionary Microbiology. https://doi.org/10.1099/ijsem.0.003838.
DOI: https://doi.org/10.1099/ijsem.0.003838

Interpretive Summary: Disease losses due to microbial pathogens are a significant cost to catfish producers, and detection and monitoring of emerging pathogens is critical to protect commercial fish production. The genetic and physiological characteristics of an Erysipelothrix strain that was associated with disease losses in ornamental fish were defined. Genomic sequencing and biochemical assays defined this strain as a new species. While this species is currently found in catfish ponds, it has not yet been correlated with morbidity or mortality. This research provides a reference genome and metabolic data against which isolates from future outbreaks may be compared.

Technical Abstract: An emergent disease of ornamental fish is associated with an Erysipelothrix sp. positive for the surface protective antigen (spa) C gene. Whole genome sequencing was performed on five spaC Erysipelothrix isolates from diseased ornamental fish. In addition, spaC Erysipelothrix sp. were compared to spaA, spaB and spaC positive Erysipelothrix spp. isolated from terrestrial and marine mammals, avian species, and fish using multi-locus sequence typing (MLST). The fish pathogenic spaC isolates were genetically distinct from E. rhusiopathiae, sharing 86.8-86.9% average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values of 32-32.1%; but 99-99.1% ANI and 90.8-91.9% dDDH values with the uncharacterized spaC positive Erysipelothrix sp. strain 2 isolated from swine. Findings indicate the spaC positive fish and swine isolates are conspecific and represent a previously unrecognized taxon. While phylogenies inferred from MLST sequences confirm this conclusion, slight genetic differences between the spaC fish isolates and swine strain 2 were indicated. Bath immersion challenge trials were conducted using tiger barbs (Puntigrus tetrazona) exposed to 107 CFU/ml of eight different Erysipelothrix spp. isolates (three from spaAand spaC type, and two from spaB) as a model of infection. After 30 days, cumulative mean percent survival was 37% for spaA, 100% for spaB, and 13% for the spaC isolates, revealing differences in virulence among the various spa genotypes in fish. Genetic findings and observed differences in virulence demonstrate that fish pathogenic spaC isolates represent a novel species, for which the name Erysipelothrix piscisicario sp. nov. is proposed. Importance: According to the Food and Agriculture Organization, exports from the United States ornamental fish industry exceed 300 million dollars annually. Outbreaks of disease in cultured fish are a major impediment to profitability, causing losses in the billions of dollars worldwide. Before 2014, Erysipelothrix spp. were believed to be commensal organisms in fish. Since that time, outbreaks of low to moderate mortality caused by Erysipelothrix spp. have occurred on aquaculture farms producing food and ornamental fish in Australia and the United States, respectively. Results of this and other studies reveal a novel emerging fish pathogen distinct from Erysipelothrix rhusiopathiae which we describe and propose as Erysipelothrix piscisicario sp. nov., a new member in the genus Erysipelothrix.