Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Karsi, Attila

Committee Member

Peterson, Daniel G.

Committee Member

Pinchuk, Lesya M.

Committee Member

Lawrence, Mark L.

Date of Degree

12-8-2017

Original embargo terms

Worldwide

Document Type

Dissertation - Open Access

Major

Veterinary Medical Sciences

Degree Name

Doctor of Philosophy

College

College of Veterinary Medicine

Department

Department of Basic Sciences

Abstract

Catfish, the "king" of the U.S. aquaculture, is threatened by a severe, systemic bacterial disease known as enteric septicemia of catfish (ESC). This disease causes high mortality and massive economic losses in cultured channel catfish (Ictalurus punctatus) in the United States. E. ictaluri penetrates catfish intestinal epithelia quickly and establishes a systemic infection rapidly. However, our knowledge on catfish intestine and E. ictaluri interaction is very limited. In Particular, catfish intestinal immune responses and virulence genes needed by E. ictaluri to evade host defenses are not well understood. Hence, our long-term goal is to identify the molecular mechanisms of E. ictaluri-host interactions. The overall objectives of this study were to understand catfish immune responses to E. ictaluri infection and determine essential genes of E. ictaluri during the intestinal invasion. To accomplish the overall objectives of this research, intestinal ligated loops were constructed surgically in live catfish and loops were injected with wild-type E. ictaluri and two live attenuated E. ictaluri vaccine strains developed recently by our research group. We first determined catfish intestinal immune responses against E. ictaluri wild-type and live attenuated vaccine strains. Then, we analyzed the global gene expression patterns of wild-type E. ictaluri and vaccine strains during catfish intestinal invasion using high throughput RNA-Seq technology. Results showed a moderate level of neutrophil and B cell infiltration correlated with significantly lower expression of TNF-α, CD4-1, and CD8-α in the vaccine injected intestinal tissue compared to that of wild-type injected intestinal tissue. Further, RNA-Seq data analysis showed the prominent expression of genes related to bacterial secretion systems, ATP production processes, and multidrug resistance (MDR) efflux pumps in wild-type E. ictaluri. In contrast, the prominently expressed genes in vaccine strains were related to the phosphotransferase system and sugar metabolism processes. All these data suggest that our live attenuated vaccines are capable of triggering effective immune responses in catfish without causing damage to the host.

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