Theses and Dissertations


Neeti Dahal

Issuing Body

Mississippi State University


Lawrence, Mark L.

Committee Member

Karsi, Attila

Committee Member

Pharr, G. Todd

Committee Member

Donaldson, Janet R.

Date of Degree


Document Type

Dissertation - Open Access


Veterinary Medical Science

Degree Name

Doctor of Philosophy (Ph.D)


College of Veterinary Medicine


Veterinary Medical Science Program


Edwardsiella ictaluri is the causative agent of enteric septicemia of catfish (ESC), which is the most economically important disease of farm-raised channel catfish. E. ictaluri is considered a facultative intracellular pathogen like other well-known species in the Enterobacteriaceae, and it is capable of surviving inside channel catfish neutrophils and macrophages. Its ability to survive inside neutrophils and macrophages has made the development of an effective vaccine against ESC particularly challenging. The goal is to develop a safe, efficacious live attenuated ESC vaccine that is practical and economically beneficial to catfish producers. In this study, single and combination of mutations in genes encoding TCA cycle enzyme and C-1 metabolism proteins were constructed using inrame mutagenesis. The virulence, vaccine efficacy, and tissue persistence of the constructed single and combination mutants were determined in channel catfish. The constructed mutants EideltasdhC, Eideltamdh, EideltafrdA, EideltaglyA, EideltasdhCdeltamdh, EideltasdhCdeltafrdA, and EideltasdhCdeltagcvP were significantly attenuated and showed 100% protection against E. ictaluri 93-146 infection in juvenile channel catfish. However, when tested in 15-d old catfish fry, mutant EideltasdhCdeltagcvP and EideltafrdA were found to provide good protection (99% and 60%, respectively) against E. ictaluri 93-146 infection. The tissue persistence study indicated higher tissue concentration in mutants EideltasdhCdeltagcvP and EideltafrdA relative to the tissue concentration in EideltasdhC and EideltasdhCdeltafrdA mutants.