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ARS Home » Southeast Area » Stoneville, Mississippi » Warmwater Aquaculture Research Unit » Research » Publications at this Location » Publication #318507

Research Project: Umbrella Project for Food Safety

Location: Warmwater Aquaculture Research Unit

Title: Real-time assays for detection and quantification of Edwardsiella tarda, Edwardsilla piscicida and Edwardsiella piscicida-like sp. in catfish tissues and pond water

item Reichley, Stephen - Mississippi State University
item Ware, Cynthia - Mississippi State University
item Greenway, Terrence - Mississippi State University
item Wise, David - Mississippi State University
item Griffin, Matthew - Mississippi State University

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2015
Publication Date: 3/1/2015
Citation: Reichley, S.R., Ware, C., Greenway, T.E., Wise, D.J., Griffin, M.J. 2015. Real-time assays for detection and quantification of Edwardsiella tarda, Edwardsilla piscicida and Edwardsiella piscicida-like sp. in catfish tissues and pond water. Journal of Veterinary Diagnostic Investigation. 27(2):130-139.

Interpretive Summary: Species specific, real-time PCR assays provide rapid molecular identification of the phenotypically ambiguous fish pathogens. Experimental disease challenges demonstrate the quantifiable nature of the assays, which can be used to estimate bacterial burden in clinically and sub-clinically infected fish. In addition, this work identified differences in pathogenicity between these bacteria in experimentally exposed juvenile channel catfish. The establishment of a consistent disease challenge model is required to adequately assess the potential for disease related losses attributed to these Edwardsiella species. The pathogenesis of E. tarda in channel catfish has been well documented, although these studies took place prior to the adoption of E. piscicida and the true identity of the isolate used has been called into question. Similarly, the susceptibility of hybrid catfish to these genetic variants is unknown. Controlled studies must be performed using these genetic strains to evaluate and properly document the pathology of these organisms and their effects on blue, channel and hybrid catfish. This effort is an invaluable first step in laying the groundwork for developing and evaluating efficacious control measures to lessen the impact of this potential emerging disease.

Technical Abstract: Researchers have proposed the adoption of 3 distinct genetic taxa among bacteria previously classified as Edwardsiella tarda; namely E. tarda, E. piscicida, and a taxon presently termed E. piscicida–like. Individual real-time polymerase chain reaction (qPCR) assays were developed, based on previously published primers, for E. tarda, E. piscicida, and E. piscicida–like sp. to provide rapid quantitative confirmatory tests for these phenotypically ambiguous bacteria. In addition to quantifying target bacteria from various substrates, the assays provide rapid identification, differentiation, and confirmation of the phenotypically indistinguishable E. tarda, E. piscicida, and E. piscicida–like sp., a valuable tool for diagnostic assessments.