Date of Award

2023

Degree Type

Open Access Thesis

Degree Name

Master of Science (MS)

Department

Biological Sciences

First Advisor

Marcia M. Pierce

Abstract

Listeria monocytogenes is an opportunistic pathogen that can cross the protective placental barrier and infect the fetus, leading to congenital disabilities or death. Extracellular L. monocytogenes infection of the placenta has been well studied; however, the bacteria have not been observed translocating this barrier intracellularly. As an intracellular pathogen, L. monocytogenes could infect phagocytic cells that can be transported across the placental barrier. A novel cell co-culture system comprised of BeWo and HPVEC cell lines was established to model the human placental barrier. Barrier integrity was confirmed using immunostaining of tight junctions and a FITC-dextran permeability assay. The model was then used to observe L. monocytogenes use of the “Trojan horse” method for vertical transmission. Human monocyte THP-1 cells were exposed to L. monocytogenes (MOI 100) for one hour to ensure infection. The co-culture model was exposed to varying treatments including the L. monocytogenes-infected THP-1s for two hours to allow translocation. Upon exposure to the infected cells, the placental model experienced a five-fold increase in barrier permeability. Hemocytometer counts revealed a significant increase in cell translocation with treatments that included THP-1s infected with L. monocytogenes. Model exposure to monocytes infected with L. monocytogenes resulted in an increase in sICAM-1 expression (~3-fold) and an increase in cell cytotoxicity by ~20%. Immunostaining of co-culture models exposed to L. monocytogenes-infected monocytes revealed severe disruption of occludin and claudin-1 tight junctions. This study demonstrates Listeria usage of the Trojan horse mechanism to reach and translocate the human placental barrier. Thus, Listeria infection can utilize both extracellular and intracellular forms of the pathogen to breach the placental barrier.

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