Honors Theses


Yvonne Sun, Ph.D.



Publication Date


Document Type

Honors Thesis


Listeria monocytogenes is a prevalent food-borne pathogen, and a clear understanding of its pathogenesis can enhance our capability to treat infections. L. monocytogenes is ingested through contaminated foods, enters the intestinal lumen, and is able to spread throughout the rest of the body. The intracellular life cycle of L. monocytogenes requires the regulated expressions of a variety of virulence genes. We previously found that exposure to short chain fatty acids (SCFAs), fermentation byproducts present in the intestines, resulted in significant changes in L. monocytogenes pathogenesis. This research, divided into two major projects, aimed to understand the relationship between L. monocytogenes, its host, and the exposure to SCFAs. Project one evaluated the effect of prior anaerobic exposure of SCFAs, specifically propionate, on strain 07PF0776, a cardiotropic clinical isolate. Hemolytic assays were used to measure the activity of secreted LLO as an indication of bacterial virulence. This project also assessed intracellular growth and actin polymerization of L. monocytogenes in cardiac myoblast cells and macrophages. To further investigate the mechanism underlying L. monocytogenes response to SCFAs, project two explored the role of CodY, a transcription factor in response to levels of branched chain amino acids, in the opposing effects of propionate on LLO production. By comparing the culture supernatant LLO activities in strain 10403s and a mutant with a codY gene deletion (ΔcodY), I discovered that CodY was required for the increase in LLO production in response to anaerobic propionate exposure. Together, the results of these projects provide further evidence for the relationship between SCFA exposure and L. monocytogenes pathogenesis. Ultimately, these findings can be utilized to improve the understanding of L. monocytogenes and develop effective prevention and treatment methods.

Permission Statement

This item is protected by copyright law (Title 17, U.S. Code) and may only be used for noncommercial, educational, and scholarly purposes.


Undergraduate research