Listeria monocytogenes (Lm) is a Gram-positive bacterium that causes the severe food-borne disease listeriosis. Listeriosis is particularly problematic in pregnant women as Lm colonizes the placenta, resulting in adverse pregnancy outcomes including stillbirth, miscarriage, and preterm labor. Despite numerous studies of placental listeriosis (PL) in various animal models, the mechanisms driving adverse outcomes following PL are largely uncharacterized. This dissertation addresses some of the field's knowledge gaps by analyzing the changes in placental gene expression and metabolism following infection with Lm and by characterizing a key Lm virulence factor, Internalin P (InlP), which plays a significant role in Lm placental colonization. Chapter 1 gives pertinent background information on the placenta, Lm, and PL and broadly addresses the knowledge gaps to be addressed by the rest of the dissertation.Chapter 2 describes an in vivo study of PL in mice. Infected and control placentas were analyzed for differences in gene expression profiles between the two groups. We identified an enrichment of genes associated with eicosanoid biosynthesis, suggesting perturbations in eicosanoid metabolism in infected tissues. By quantifying placental eicosanoid concentrations through mass spectrometry, we found a significant increase in the concentrations of several eicosanoids with known roles in inflammation and/or labor. This study provides a likely explanation for temporal disruptions of labor following placental infection.Chapters 3 and 4 discuss two studies of the Lm virulence factor InlP, a key player in placental colonization. InlP contributes to Lm's placental pathogenesis likely by conferring the ability of Lm to transcytose through placental layers. Prior studies reported that no homologs of InlP exist in Listeria species other than Lm. Chapter 3 describes our discovery that at least two other Listeria species, L. ivanovii and L. seeligeri, encode InlP homologs. We characterized the domain architectures and genomic neighborhoods of these homologs and speculated on their implications for Listeria evolution.In chapter 4, I continue discussion of InlP and describe our identification and preliminary characterization of naturally occurring InlP variants. In this study, we used a bioinformatics approach to analyze Lm whole genome sequences (WGS) and identify InlP variants. We uncovered two InlP variants of interest in the Lm population. The first results from a start codon point mutation in the inlP gene, likely resulting in a truncated and potentially nonfunctional InlP protein product. The second is an InlP variant with a PRO to SER substitution in the InlP calcium binding loop, which is hypothesized to play a role in InlP activation or stabilization. These results provide two avenues for further investigation of InlP regulation and function and suggest the potential for InlP-dependent variation in placental colonization potential across Lm isolates. In chapter 5, I summarize this dissertation. This chapter reflects on the results, implications, and challenges of each study outlined in the prior chapters. I discuss the unique challenges faced due to the ongoing COVID-19 pandemic and its effects on my graduate training. Finally, I share concluding remarks and propose future directions for this project and the field of PL. Together, the chapters of this dissertation describe novel findings that contribute to the field by assessing genetic and metabolic changes to the placenta due to listeriosis and further characterizing a known key placental virulence factor.
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