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Diseases of Aquatic Organisms

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DAO 106:17-29 (2013)  -  DOI:

Comparison of Vietnamese and US isolates of Edwardsiella ictaluri 

Matthew L. Rogge1,*, Lidiya Dubytska1,*, Tae Sung Jung2, Judy Wiles1, Ahmad A. Elkamel3, Amelia Rennhoff1, Dang Thi Hoang Oanh4, Ronald L. Thune1,5,**

1Department of Pathobiological Sciences, Louisiana State University School of Veterinary Medicine, Baton Rouge, Louisiana 70803, USA
2Aquatic Biotechnology Center of WCU Project, Lab of Aquatic Animal Diseases, College of Veterinary Medicine, Gyeongsang National University, Jinju, Gyeongnam 660-701, South Korea
3Fish Diseases and Management, Department of Animal Medicine, Faculty of Veterinary Medicine, Assiut University, Egypt
4Department of Aquatic Biology and Pathology, College of Aquaculture and Fisheries, Cantho University, Cantho City, Vietnam
5School of Animal Science, Louisiana State University Agricultural Center, Louisiana State University, Baton Rouge, Louisiana 70803, USA
*These authors contributed equally to this work.
**Corresponding author. Email:

ABSTRACT: We compared Edwardsiella ictaluri from striped catfish in Vietnam with US channel catfish isolates. Biochemical analyses and sequencing of the 16S rRNA gene confirmed that the Vietnamese isolates were E. ictaluri. Comparison using rep-PCR fingerprinting demonstrated no significant differences between the isolates, but plasmid analysis indicated that the Vietnamese isolates grouped into 4 plasmid profiles, each different from the typical pEI1 and pEI2 plasmid profile found in the US isolates. Sequencing plasmids representative of the 4 profiles indicated that all contained derivatives of the E. ictaluri plasmid pEI1, whereas only 1 contained a plasmid derivative of the E. ictaluri plasmid pEI2. The pEI2 encoded type III secretion effector, EseI, and its chaperone, EscD, were found to be present on the chromosome in isolates lacking a pEI2 derivative. In addition, 1 isolate carried a 5023 bp plasmid that does not have homology to either pEI1 or pEI2. Furthermore, Vietnamese isolates were PCR positive for the type III and type VI secretion system genes esrC and evpC, respectively, and the urease enzyme, but were PCR-negative for the putative type IV secretion system gene virD4. A monoclonal antibody against the lipopolysaccharide of E. ictaluri ATCC 33202 did not react with the Asian isolates or with the more recent US isolates. Antibiotic resistance patterns were variable and did not correlate to the presence of any particular plasmid profile. Finally, the Vietnamese isolates were avirulent and had a significantly reduced capacity for intracellular replication within head-kidney-derived channel catfish macrophages.

KEY WORDS: Edwardsiella ictaluri · Catfish · Genotype · Plasmid · Virulence · Antibiotics

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Cite this article as: Rogge ML, Dubytska L, Jung TS, Wiles J and others (2013) Comparison of Vietnamese and US isolates of Edwardsiella ictaluri . Dis Aquat Org 106:17-29.

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