Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Lawrence, Mark L.

Committee Member

Hanson, Larry

Committee Member

Karsi, Attila

Committee Member

Pinchuk, Lesya M.

Date of Degree

8-8-2023

Document Type

Dissertation - Open Access

Major

Infectious disease

Degree Name

Doctor of Philosophy (Ph.D)

College

College of Veterinary Medicine

Department

Department of Comparative Biomedical Sciences

Abstract

Virulent Aeromonas hydrophila (vAh) is a causative agent of motile Aeromonas septicemia (MAS) in catfish. There are limitations in the current therapeutic and preventative strategies against vAh. The pathogenesis of MAS as well as the immune response of catfish to vAh infection are poorly understood. The aim of this study is to: 1) develop a dual live attenuated vaccine against MAS and enteric septicemia of catfish caused by Edwardsiella ictaluri; and 2) evaluate the vAh bacterial load and gene expression patterns in catfish tissues following vAh infection. Previously, six recombinant vAh proteins (outer membrane protein, TonB-dependent receptor, three fimbrial proteins, and an ATPase) were identified to have vaccine efficacy against MAS, and live attenuated E. ictaluri vaccine strain ESC-NDKL1 was identified as an effective vector for expressing vAh antigens. A total of 29 recombinant ESC-NDKL1 strains have been constructed with the integration of one, two, or three genes encoding vAh antigens into the ESC-NDKL1 chromosome. Vaccine efficacy of the constructed strains was evaluated in channel catfish fingerlings. Four recombinant ESC-NDKL1 strains expressing two vAh antigens (ESC-NDKL1::atpase::fimMrfG, ESC-NDKL1::fim::fimMrfG, ESC-NDKL1::tdr::fimMrfG, and ESC-NDKL1::fim::ompA) showed significant protection against MAS with relative percent of survival (RPS) values of 55.72%, 60.18%, 61.74%, and 54.81%. Four triple recombinant ESC-NDKL1 strains (ESC-NDKL1::fimMrfG::ompA::fimA, ESC-NDKL1::atpase::fimMrfG::ompA, ESC-NDKL1::fim::fimMrfG::ompA and ESC-NDKL1::atpase::tdr::fim) showed the best protection with RPS values of 77.93%, 63.18%, 67.74%, and 82.35%. To gain a better understanding of vAh pathogenesis, catfish fingerlings were intraperitoneally injected with vAh strain ML09-119. The anterior kidney, liver, and spleen were collected for determination of vAh distribution and expression of thirteen pro-inflammatory, innate, and adaptive immune-related genes using real-time PCR. Results revealed that vAh spread into catfish tissues within 2 hours and peaked at 12 hours post-infection. vAh infection initiated a strong inflammatory response in catfish tissues. Additionally, our research revealed that surviving catfish were able to develop a primary immune response and possibly generation of memory B cells against MAS. Such information will facilitate the development of vaccines and therapeutic drugs for preventing and treating MAS outbreaks in catfish aquaculture.

Download

Available for download on Friday, August 15, 2025

Share

COinS