Recombinant Probiotic Expressing <em>Listeria</em> Adhesion Protein Attenuates <em>Listeria monocytogenes</em> Virulence <em>In Vitro</em>

<div><h3>Background</h3><p><em>Listeria monocytogenes</em>, an intracellular foodborne pathogen, infects immunocompromised hosts. The primary route of transmission is through contaminated food. In the gastrointestinal tract, it traverses the epithelial barrier through intracellular or paracellular routes. Strategies to prevent <em>L. monocytogenes</em> entry can potentially minimize infection in high-risk populations. <em>Listeria</em> adhesion protein (LAP) aids <em>L. monocytogenes</em> in crossing epithelial barriers via the paracellular route. The use of recombinant probiotic bacteria expressing LAP would aid targeted clearance of <em>Listeria</em> from the gut and protect high-risk populations from infection.</p> <h3>Methodology/Principal Findings</h3><p>The objective was to investigate the ability of probiotic bacteria or LAP-expressing recombinant probiotic <em>Lactobacillus paracasei</em> (Lbp^LAP) to prevent <em>L. monocytogenes</em> adhesion, invasion, and transwell-based transepithelial translocation in a Caco-2 cell culture model. Several wild type probiotic bacteria showed strong adhesion to Caco-2 cells but none effectively prevented <em>L. monocytogenes</em> infection. Pre-exposure to Lbp^LAP for 1, 4, 15, or 24 h significantly (<em>P</em><0.05) reduced adhesion, invasion, and transepithelial translocation of <em>L. monocytogenes</em> in Caco-2 cells, whereas pre-exposure to parental <em>Lb. paracasei</em> had no significant effect. Similarly, Lbp^LAP pre-exposure reduced <em>L. monocytogenes</em> translocation by as much as 46% after 24 h. Lbp^LAP also prevented <em>L. monocytogenes</em>-mediated cell damage and compromise of tight junction integrity. Furthermore, Lbp^LAP cells reduced <em>L. monocytogenes</em>-mediated cell cytotoxicity by 99.8% after 1 h and 79% after 24 h.</p> <h3>Conclusions/Significance</h3><p>Wild type probiotic bacteria were unable to prevent <em>L. monocytogenes</em> infection <em>in vitro</em>. In contrast, Lbp^LAP blocked adhesion, invasion, and translocation of <em>L. monocytogenes</em> by interacting with host cell receptor Hsp60, thereby protecting cells from infection. These data show promise for the use of recombinant probiotics in preventing <em>L. monocytogenes</em> infection in high-risk populations.</p>