Edwardsiella ictaluri as the Causative Agent of Mortality in Cultured Nile Tilapia

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 naive tilapia, reproducing clinical signs and mortality, thereby establishing Koch's postulates.

High-throughput discrimination of bacteria isolated fromAstacus astacusandA. leptodactylus

“…When performing health status evaluations, considering correct identification and treatment of bacterial diseases and conditions, of (primarily) farmed crayfish, speed is always an issue. Rapid identification of environmental bacteria via commercial phenotypic tests allows for a wide choice of tests selection, and API 20E (Biomerieux, Marcy l'Etoile, France), an identification system for Enterobacteriaceae and other non-fastidious Gram-negative rods developed for clinical specimens, seems to be increasingly used for the identification of aquatic pathogens (Topić Popović et al, 2007;Sanjuán et al, 2009;Bastardo et al, 2012;Esteve et al, 2012;Soto et al, 2012). However, due to several shortcomings of this system, such as the wrong identifications and the need of comparison with the diagnostic schemes based on reactions in conventional phenotypic tests, more advanced methods for identification are sought after.…”

Bacterial distribution and tissue targets following experimental Edwardsiella ictaluri infection in Nile tilapia Oreochromis niloticus

“…In Edwardsiella ictaluri-infected tilapia, the most consistently reported findings are multifocal nodulations in the spleen, head kidney, and hepato megaly with a reduced fat reserve in the liver and peritoneal cavity. Moreover, microscopically, a severe chronic inflammatory infiltrate is observed in the spleen, head kidney, and liver, with multifocal areas of necrosis and granuloma formation (Soto et al 2012).The use of experimental animal models remains critical to elucidating disease pathogenesis, especially when studying emergent diseases. In the present study, we used quantitative real-time PCR (qPCR) and histological analysis to evaluate the dissemination of Edwardsiella ictaluri in Nile tilapia under controlled conditions.…”

Vaccine efficacy of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from Edwardsiella ictaluri against E. tarda in tilapia

“…Moreover, the strain OT9606S (isolated from Chinese catfish) demonstrated low or no pathogenicity to tilapia in our previous study (unpublished data). In consideration of these previous results, for development of an effective vaccine against E. ictaluri for tilapia, strains should be chosen from tilapia, such as those reported by Soto et al (2012). Additionally, as described in our previous study on S. agalactiae, a group receiving ISA with PBS and a group only receiving PBS as control were used for vaccine experiments in tilapia.…”