Date of Graduation

8-2016

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Food Science (PhD)

Degree Level

Graduate

Department

Food Science

Advisor

Philip G. Crandall

Committee Member

Steven Ricke

Second Committee Member

Michael Johnson

Third Committee Member

Young-Min Kwon

Fourth Committee Member

Jim Rankin

Abstract

Listeria spp. are often isolated from raw and processed food products. Listeria monocytogenes is responsible for death rates of 10 to 30% in immune compromised people; it can also infect a vast range of animals. There are numerous reports of poultry harboring or becoming infected with L. monocytogenes. First, this research assessed the ability of L. monocytogenes to replicate within chicken macrophages. Using the gentamicin-killing assay, a cell culture of chicken macrophage-like cells (HD11) were infected with two strains of L. monocytogenes individually (EGD-e and Scott A). Results show that unlike data on mouse macrophages, intracellular L. monocytogenes do not reduce (P<0.05) chicken macrophage viability until after 11 hours post-infection. While requiring a number of essential nutrients to grow, Listeria spp. have unique metabolic and regulatory networks which allow them to survive a variety of extreme conditions including low pH, high osmotic pressure, desiccation, and starvation. Second, this research extended previous work on starvation. L. monocytogenes strains EGD-e, Scott A, HCC23, and F2365 were starved individually at 4°C in sterile water with 100 rpm agitation for up to 6 weeks. Spread and track plate counts indicate populations slowly died off. In addition, starved cells were subjected to a number of metabolic inhibitors. The results suggest that cells are gaining energy in the form of ATP between glyceraldehyde-3-phosphate and phosphoenolpyruvate in glycolysis. Further research on the ATP production and other active metabolic processes under starvation should be undertaken to explore the metabolic capabilities of these cells. This research has implications for why L. monocytogenes show up in some food products and not others. In addition, it highlights the strain-to-strain variation of L. monocytogenes.

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