Evaluation of Zebrafish Danio rerio as a Model for Enteric Septicemia of Catfish (ESC)

Abstract

Zebrafish (also known as zebra danio) Danio rerio were injected intramuscularly with Edwardsiella ictaluri at doses of 6 x 10(3), 6 x 10(4), or 6 x 10(5) colony-forming units per gram (CFU/g) or sterile phosphate-buffered saline (sham) or were not injected. Mortality occurred from 2 to 5 d postinjection (dpi) at rates of 0, 76.6, and 81.3% for the low, medium, and high doses, respectively, and E. ictaluri was isolated from dead fish. Survivors were sampled at 10 dpi and E. ictaluri was not isolated. Sham-injected and noninjected controls did not suffer mortality. Histopathology trials were performed in which zebrafish were injected with 1 x 10(4) CFU/g or sham-injected and sampled at 12, 24, 48, 72, and 96 h postinjection for histological interpretation. Collectively, these zebrafish demonstrated increasing severity of splenic, hepatic, cardiac, and renal interstitial necrosis over time. To evaluate the progression of chronic infection, zebrafish were injected with 1 x 10(2) CFU/g and held for 1 month postinjection. Beginning at 12 dpi and continuing for an additional 2 weeks, zebrafish demonstrated abnormal spiraling and circling swimming behaviors. Histopathology demonstrated necrotizing encephalitis. In immersion trials, zebrafish were exposed to low, medium, and high doses (averaging 1.16 x 10(5), 1.16 x 10(6), and 1.16 x 10(7) CFU/mL of tank water) of E. ictaluri for 2 h. Mortality occurred from 5 to 9 d postexposure at rates of 0, 3.3, and 13.3% for the low, medium, and high doses, respectively; E. ictaluri was isolated from dead fish. Channel catfish Ictalurus punctatus exposed to the medium doses suffered 100% mortality, and E. ictaluri was isolated from these fish. This study demonstrates the potential use of zebrafish as a model for E. ictaluri pathogenesis.

Evidence for a core gut microbiota in the zebrafish

“…Moreover, the bacterial taxa that dominated the intestines of recently caught zebrafish were largely the same as those dominating the intestines of domesticated zebrafish. One notable exception was the genus Edwardsiella, which includes the freshwater fish pathogens E. tarda and E. ictaluri (Plumb, 1999;Pressley et al, 2005;Petrie-Hanson et al, 2007). Edwardsiella spp.…”

Mechanisms of intrinsic resistance to antimicrobial peptides of Edwardsiella ictaluri and its influence on fish gut inflammation and virulence

“…Zebrafish challenges were performed according to previously described methodology (Petrie- Hanson et al, 2007) with modifications (Santander et al, 2011). The water temperature was 26±1 uC; the fish were acclimatized over 2 weeks before experimentation.…”

“…Two sets of controls were used: fish that were injected with 10 ml of sterile PBS and fish that were not injected. Moribund fish demonstrating clinical signs were killed and necropsied, and bacteria isolated as previously described (Petrie- Hanson et al, 2007). Survivors of each dose at 6 weeks post-injection were challenged with 10 6 c.f.u.…”

“…Zebrafish is not the natural host of E. ictaluri, but has been established as a reliable model system to evaluate E. ictaluri virulence (Petrie- Hanson et al, 2007;Santander et al, , 2011. We found that E. ictaluri DwibT and Dgne administered intramuscularly (i.m.)…”

Recommendations for Health Monitoring and Reporting for Zebrafish Research Facilities

“…48 Edwardsiella ictaluri is a Gram-negative bacterium responsible for causing high mortality epizootics in zebrafish characterized by severe systemic infection with necrotizing inflammation in various visceral organs and associated morbidity and mortality. 49,50 It is transmitted by direct contact, water, feces, and orally. Although this pathogen may be susceptible…”