Date of Award

January 2020

Degree Type

Open Access Thesis

Document Type

Master Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Marcia M. Pierce

Department Affiliation

Biological Sciences

Second Advisor

Oliver R. Oakley

Department Affiliation

Biological Sciences

Third Advisor

Patrick J. Calie

Department Affiliation

Biological Sciences

Abstract

In the U.S., Listeria monocytogenes accounts for less than one percent of foodborne illnesses but has a 28% mortality rate. Infection in healthy individuals causes colonization of the intestinal lumen and subclinical noninvasive listeriosis. However, translocation of L. monocytogenes across the intestinal epithelium produces invasive systemic listeriosis with central nervous system involvement. Little is known of the gastrointestinal stages of L. monocytogenes pathogenesis. Enteric pathogens such as L. monocytogenes interact directly with the host-microbiota during the gastrointestinal phase of pathogenesis. Recent research has recognized that microbiota plays a role in activating immune response and protecting against invasive pathogens. Individual host microbiota is highly variable; however, the phyla Firmicutes and Bacteroidetes commonly dominate the gut. The epithelial layer is predominantly colonized by species from the genera Bacteroides, Streptococcus, Lactobacillus, Enterococcus, Bifidobacterium, Ruminococcus, Clostridium, and members of the Enterobacteriaceae. In contrast, the mucosa is dominated by species from the genera Clostridium, Lactobacillus, Enterococcus, and Akkermansia. Species from the phylum Firmicute have been recognized as providing direct and indirect colonization resistance against infection by L. monocytogenes. In our preliminary experiments, gut microbial diversity was determined using 16S rRNA sequencing on 22 cecum samples from female CD1 mice. We determined that Firmicute bacteria are prominent at all stages of the estrus cycle; however, increased Firmicute density was observed at the estrus and diestrus stages (DE), dominating over 50% of the gut microbial diversity (64.1% and 65.8%, respectively). The objective of this study was to determine if the increase in density of Firmicute within estrus and diestrus decrease the number of bacteria translocating across the epithelial barrier. 6-9-week female BALB/cj were infected with 1x108 bacterial cells using a foodborne infection model before being euthanized at 24, 48, and 72 hours post-infection. Translocation of L. monocytogenes across the intestinal barrier was determined by fractionation of the intestine into five fractions, luminal, mucosal, intracellular, lamina propria, and extracellular. The results did not show a significant difference in translocation between DE mice compared to proestrus and metestrus (PM) mice. A significant decrease in luminally and mucosa-associated L. monocytogenes was found at 24- and 48-hours post infection (p.i.). Interestingly 48 hours p.i. the mean L. monocytogenes within the luminal and lamina propria fractions was significantly higher in estrus and diestrus compared to proestrus and metestrus stage mice.

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