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United States Department of Agriculture

Agricultural Research Service

Research Project: Integrated Aquatic Animal Health Strategies

Location: Aquatic Animal Health Research

Title: Edwardsiella tarda and Aeromonas hydrophila isolated from diseased Southern flounder (Paralichthys lethostigma) are virulent to channel catfish and Nile tilapia

Authors
item Wei Pridgeon, Yuping
item Klesius, Phillip
item Lewbart, Gregary -
item Daniels, Harry -
item Jacobs, Megan -

Submitted to: Journal of Coastal Life Medicine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 30, 2014
Publication Date: April 23, 2014
Citation: Wei Pridgeon, Y., Klesius, P.H., Lewbart, G.A., Daniels, H.V., Jacobs, M. 2014. Edwardsiella tarda and Aeromonas hydrophila isolated from diseased Southern flounder (Paralichthys lethostigma) are virulent to channel catfish and Nile tilapia. Journal of Coastal Life Medicine. 2(5):337-343.

Interpretive Summary: A total of 25 Gram-negative bacteria were isolated from diseased Southern flounder (Paralichthys lethostigma). Based on biochemical analysis, the 25 isolates were found to share homologies with either Edwardsiella tarda or Aeromonas hydrophila. Based on sequencing results of partial 16S rRNA gene, 15 isolates shared 100% identities with the 16S rRNA sequence of E. tarda strain TX1, whereas the rest 10 isolates shared 100% identities with the 16S rRNA sequence of A. hydrophila strain An4. When healthy fish were exposed to flounder isolate by injection, the LD50 value of flounder isolate E. tarda to channel catfish and Nile tilapia (10±2g) was 6.1 × 104 and 1.1 × 107 CFU/fish, respectively, whereas that of flounder isolate of A. hydrophila to channel catfish and Nile tilapia was 1.4 × 107 and 5.6 × 107 CFU/fish, respectively. This is the first report that E. tarda and A. hydrophila isolated from diseased Southern flounder are virulent to catfish and tilapia.

Technical Abstract: The aim of this study is to identify bacterial pathogens isolated from diseased Southern flounder and determine their virulence to channel catfish and Nile tilapia. Twenty five Gram-negative bacteria isolates were recovered from five tissues (skin lesions, brain, liver, intestine, and posterior kidney) of diseased Southern flounder (Paralichthys lethostigma). Based on API 20NE and fatty acid methyl ester analysis, the 25 isolates were found to share homologies with either Edwardsiella tarda or Aeromonas hydrophila. Based on sequencing results of partial 16S rRNA gene, 15 isolates shared 100% identities (e value = 0) with the 16S rRNA sequence of E. tarda strain TX1 (GenBank EF467363), whereas the other 10 isolates shared 100% identities (e value = 0) with the 16S rRNA sequence of A. hydrophila strain An4 (GenBank FJ386959). When healthy fish were exposed to flounder isolate by intraperitonal (IP) injection, the LD50 value of flounder isolate E. tarda to channel catfish and Nile tilapia (10±2g) was 6.1 × 104 and 1.1 × 107 CFU/fish, respectively, whereas that of flounder isolate of A. hydrophila to channel catfish and Nile tilapia was 1.4 × 107 and 5.6 × 107 CFU/fish, respectively. This is the first report that E. tarda and A. hydrophila isolated from diseased Southern flounder are virulent to catfish and tilapia.

Last Modified: 9/23/2014
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