Abstract

Edwardsiella ictaluri, a gram-negative enteric bacterium, is the known etiologic agent of enteric septicemia of catfish. In the last few years, different strains have been implicated as the causative agent of mortality events in cultured fish, including the Nile tilapia (Oreochromis niloticus). Due to the emergent nature of edwardsiellosis in non-ictalurid fish, little is known regarding the dynamics of E. ictaluri infection in tilapia. The purpose of this study was to gain a better understanding of the pathogenesis of edwardsiellosis in tilapia by determining rate of bacterial dissemination, tissue targets of infection, lethal and infective doses, and specific tissue responses to E. ictaluri following an immersion challenge with bacterial strains recovered from outbreak events in tilapia. In addition to histopathologic assessment, the bacterial burdens in several tissues of infected fish were determined over a 2-week course of infection using quantitative real-time PCR (qPCR). The collected data suggest that cutaneous and oral routes are the main ports of entry for the organism, with subsequent hematogenous dissemination throughout the body. Histopathologic examination of infected fish revealed involvement of a wide range of tissues; however, the severity of necrotizing and granulomatous lesions in the spleen and head kidney, paired with concomitant high levels of bacterial DNA as determined by qPCR, identifies these two organs as the main targets of E. ictaluri infection in Nile tilapia.

Acknowledgements

The authors thank Ross University-School of Veterinary Medicine Research Program for the support in this project. The authors declare no conflict of interests.

* Presenting author