Location: Warmwater Aquaculture Research UnitTitle: Edwardsiella ictaluri as the causative agent of mortality in cultured Nile tilapia Author
Submitted to: Journal of Aquatic Animal Health
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/30/2012
Publication Date: 5/30/2012
Citation: Soto, E., Griffin, M., Arauz, M., Martinez, A., Cabrejos, M.E. 2012. Edwardsiella ictaluri as the causative agent of mortality in cultured nile tilapia. Journal of Aquatic Animal Health. 24(2):81-90. Interpretive Summary: Edwardsiella ictaluri was isolated diseased Nile tilapia Oreochromis niloticus from a farm experiencing mortality events. The bacteria was identified via biochemical and molecular methods. Infectivity challenges confirm that the bacteria was pathogenic to tilapia. This represents the first published outbreak of Edwardsiellosis in Nile tilapia.
Technical Abstract: Edwardsiella ictaluri was consistently isolated from the spleens, livers, and head kidneys of diseased Nile tilapia Oreochromis niloticus from a farm experiencing mortality events in several culture ponds. We describe the first published outbreak of E. ictaluri–induced Edwardsiellosis in Nile tilapia. Pure cultures of the isolated bacteria were characterized both biochemically and molecularly. Biochemical analysis was performed using the API-20E and RapID One systems, and antimicrobial susceptibility was determined by the broth microdilution method. Molecular analysis involved sequencing of the 16S rRNA gene, species-specific real-time polymerase chain reaction (PCR), and PCR-mediated genomic fingerprinting (rep-PCR). Pairwise sequence analysis of the 16S rRNA gene identified the case isolates to be a 100% match to E. ictaluri cultured from channel catfish in the southeastern United States. However, rep-PCR analysis identified the case isolates to be genetically different from representative strains isolated from disease outbreaks in cultured channel catfish in Mississippi. Infectivity challenges (intraperitoneal injection and immersion) demonstrated that a representative E. ictaluri strain isolated from tilapia was pathogenic to naïve tilapia, reproducing clinical signs and mortality, thereby establishing Koch’s postulates.