Stephanie Marie Johnson



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Listeria monocytogenes is an opportunistic and intracellular food-borne pathogen that can be deadly in high risk populations. During infection in the human body, L. monocytogenes may encounter macrophages, a type of white blood cell that is critical in innate immune response both by directly targeting invading pathogens and by eliciting adaptive immune responses. During intestinal as well as peripheral infections, both L. monocytogenes and macrophages may encounter propionate, a common gut microbiome metabolite. Although propionate is shown to have various regulatory and nutritional functions, its effects on infection outcome is not well understood. Therefore, the goal of this research is to determine how the exposure to propionate by L. monocytogenes and macrophages may affect subsequent infection outcomes. Specifically, the effects of propionate on phagocytic activity of macrophages have been quantified by measuring macrophage uptake of fluorescently labeled L. monocytogenes after exposure to different propionate concentrations. Additionally, the effects of propionate on the bactericidal activities inside macrophage phagosomes was determined by quantifying the number of intracellular L. monocytogenes mutant deficient in listeriolysin O remained inside phagosomes instead of escaping into the cytoplasm. The findings of this research will provide more information on how the immune response is regulated by propionate and offer a mechanistic insight into the vast role of the gut microbiome.

Publication Date


Project Designation

Honors Thesis

Primary Advisor

Yvonne Y. Sun

Primary Advisor's Department



Stander Symposium project, College of Arts and Sciences

United Nations Sustainable Development Goals

Good Health and Well-Being

Determine the Effect of Propionate on the Interactions Between Macrophages and Listeria monocytogenes