Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Master of Science

Program

Microbiology and Immunology

Supervisor

Reid, Gregor

Abstract

Aquaculture is vital for the global food supply, but the high incidence of infectious diseases threatens the industry’s productivity. The intestinal mucosa is a key port of entry for pathogens and provides an extensive interface for host-microbe interactions. Tight junctions are at the core of gut barrier function and the mucosal health of finfish. Disruption of these complexes gives rise to sepsis, which leads to systemic inflammation and death. The present study employs a combinatorial approach that integrates in vitro and in vivo analyses to gain actionable insights into the mechanism of microbial-mediated modulation of host health. The experiments outlined in chapters 2 and 3 examine the suitability of several candidate probiotics for promoting gut barrier function, immunity, and mitigating the deleterious effects of the highly virulent aquatic pathogen Vibrio anguillarum. These studies demonstrate the importance of investigating the mechanism underlying host-microbe and microbe-microbe interactions for maximizing salmonid health.

Summary for Lay Audience

The aquaculture industry, which refers to the farming of aquatic species, is rapidly growing and its production has far surpassed that of capture hatcheries. Given that the human population will continue to increase, aquaculture must intensify its practices in the coming years to ensure the security of the global food supply. However, there are several interdependent factors that negatively impact the industry’s ability to meet these growing demands. These include competition for natural resources, climate change, and infectious diseases. The latter has become a major limiting factor for further intensification of production, and despite great developments over the past three decades, viral and bacterial infections continue to cause multibillion-dollar losses for the industry every year. Microbes are ubiquitous both within and around fish. In addition to its role in digestion, the intestinal mucosa is home to the richest and most abundant community of resident microbes that can interact with the host cells and modulate health. This interface is also a target site for the onset of infection, but supplementation of probiotic bacteria has reportedly improved disease resistance and overall physiology in several fish species. In this thesis, the concept of using beneficial microbes for the improvement of host health by interacting with the intestinal epithelium was explored with the focus on salmonid species, which are the most economically important family of finfish. By using a cell-based laboratory model of the salmonid intestine, it was found that the candidate fish probiotics could protect the cells from the highly virulent fish pathogen V. anguillarum, but the beneficial microbes had no effect on the expression of key gut barrier and immune molecules. To investigate these concepts in live animals, a disease trial was carried out at a fish farm in British Columbia. Chinook salmon were fed with diets containing different probiotic strains and were then infected with the pathogen V. anguillarum. It was found that probiotic supplementation had no effect on the survival, growth, or gene expression of immune or gut barrier molecules in the intestinal tissue. This project established the use fish cell lines for the investigation of host-microbe interactions and represents a steppingstone to guide future researchers on the study of more suitable candidate fish probiotic strains.

Creative Commons License

Creative Commons Attribution-Noncommercial 4.0 License
This work is licensed under a Creative Commons Attribution-Noncommercial 4.0 License

Available for download on Wednesday, August 24, 2022

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