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United States Department of Agriculture

Agricultural Research Service

Research Project: Genetics, Physiology, and Health Research to Improve Catfish Production

Location: Warmwater Aquaculture Research Unit

Title: Rapid quantitative detection of Aeromonas hydrophila strains associated with disease outbreaks in catfish aquaculture

Authors
item Griffin, Matt -
item Goodwin, Andrew -
item Merry, Gwenn -
item Williams, Malachi -
item Liles, Mark -
item Waldbieser, Geoffrey

Submitted to: Journal of Veterinary Diagnostic Investigation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2013
Publication Date: July 1, 2013
Citation: Griffin, M., Goodwin, A., Merry, G., Williams, M., Liles, M., Waldbieser, G.C. 2013. Rapid quantitative detection of Aeromonas hydrophila strains associated with disease outbreaks in catfish aquaculture. Journal of Veterinary Diagnostic Investigation. 25:473-481.

Interpretive Summary: A new strain of the bacteria Aeromonas hydrophila has recently been implicated in severe disease outbreaks in commercial catfish culture, leading to rapid and substantial losses of large catfish in affected ponds. This bacteria is commonly found in catfish ponds in a less virulent form, but a rapid diagnostic test was needed to determine the presence of a virulent strain. A team of scientists from Mississippi State University, the University of Arkansas-Pine Bluff, Auburn University, and the USDA-ARS-Catfish Genetics Research Unit used comparative genomics to identify differences in DNA sequence between common A. hydrophila and the new epidemic strain. A DNA-based assay was developed which provides rapid discrimination between the new epidemic strain and more common A. hydrophila from samples of fish or pond water and sediments. The assay will be helpful for more accurate diagnoses of disease outbreaks in commercial ponds, epidemiological analyses to predict future outbreaks, and monitoring of virulent bacterial populations to identify effective therapeutics.

Technical Abstract: In the summer of 2009, a new strain of Aeromonas hydrophila was implicated in severe disease outbreaks in farm-raised catfish in Alabama, Arkansas and Mississippi. These outbreaks mostly afflicted large fish and resulted in considerable losses in short periods. Given the rapid onset and biosecurity concerns associated with this new disease, a rapid diagnostic procedure to detect the new strains of A. hydrophila is needed. Ancillary to our work, a study of comparative genomics identified gene sequences specific to the virulent strains and suitable as targets for a discriminatory real-time PCR assay. Using this assay, suspect colonies on a culture plate can be positively identified as the new strain within 2 hours. The assay is repeatable and reproducible with a linear dynamic range covering 8 orders of magnitude and a sensitivity of ~7 copies of target DNA in a 15 µl reaction. In addition the assay was able to detect and quantify the virulent strain from catfish pond water and sediments with a sensitivity limit of approximately 102 bacteria in a sample. This assay provides rapid discrimination between this new epidemic strain and more common A. hydrophila and is useful for epidemiological studies involving the detection and quantification of the epidemic strain in environmental samples.

Last Modified: 11/21/2014
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