<p>The crossing of host barriers (intestinal, blood-brain, and placental) is a critical step for systemic infections caused by entero-invasive pathogens. In the intestine, the epithelial cells are the first line of defense against enteric pathogens. <i>Listeria monocytogenes</i> is a facultative-intracellular foodborne pathogen that first crosses the intestinal barrier to cause a systemic infection. However, the underlying mechanism is not well understood.</p><p><br></p> <p>We demonstrate that <i>Listeria</i> adhesion protein (LAP) promotes the translocation of <i>L. monocytogenes </i>across the intestinal barrier in mouse models (A/J and C57BL/6). Relative to the wild-type (WT; serotype 4b) or the isogenic bacterial invasion protein Internalin A mutant (Δ<i>inlA</i>) strain, the <i>lap^─</i> strain showed significant defect in translocation across the intestinal barrier and colonization of the mesenteric-lymph nodes, liver and spleen in the early phase of infection (24 h and 48 h). LAP induces intestinal epithelial barrier dysfunction for increased translocation as evidenced by increased permeability to 4-kDa FITC-dextran (FD4), a marker of paracellular permeability, in the serum and urine of WT and Δ<i>inlA</i>- infected mice and across Caco-2 cell barrier, but not the <i>lap^─</i> mutant strain. Microscopic examination confirmed localization of the WT and Δ<i>inlA</i> strains in the tight junction, a crucial barrier of intestinal paracellular permeability, in the mouse ileal tissue but the <i>lap^─</i> strain remained confined in the lumen. LAP also upregulates TNF-α and IL-6 in intestinal epithelia of mice and in Caco-2 cells for increased permeability. </p><p><br></p> <p>Investigation of the underlying molecular mechanisms of LAP-mediated increase in intestinal permeability by using <i>lap^─</i> mutant strain, purified LAP and shRNA-mediated Hsp60 suppression, we demonstrate that LAP interacts with its host receptor, Hsp60, and activates the canonical NF-κB signaling, which in turn facilitates myosin light-chain kinase (MLCK)-mediated opening of the epithelial barrier via the cellular redistribution of major epithelial junctional proteins claudin-1, occludin, and E-cadherin. Pharmacological inhibition of NF-κB or MLCK in cells or genetic ablation of MLCK in mice (C57BL/6) prevents mislocalization of epithelial junctional proteins, intestinal permeability and <i>L. monocytogenes</i> translocation across the intestinal barrier.</p> <p><br></p><p>Furthermore, LAP also promotes <i>L. monocytogenes </i>translocation across the intestinal barrier and systemic dissemination in a Mongolian gerbil that are permissive to the bacterial invasion proteins; InlA-and InlB-mediated pathways; similar to that in humans. We show a direct LAP-dependent and InlA-independent pathway<i> </i>for <i>L. monocytogenes</i> paracellular translocation across the intestinal epithelial cells that do not express luminally accessible E-cadherin. Additionally, we show a functional InlA/E-cadherin interaction pathway that aids <i>L. monocytogenes</i> translocation by targeting cells with luminally accessible E-cadherin such as cells at the site of epithelial cell extrusion, epithelial folds and mucus-expelling goblet cells. Thus, <i>L. monocytogenes</i> uses LAP to exploit epithelial innate defense in the early phase of infection to cross the intestinal epithelial barrier, independent of other invasion proteins.</p><p><br></p> <p>This work fills a critical gap in our understanding of <i>L. monocytogenes </i>pathogenesis and sheds light to the complex interplay between host-pathogen interactions for bacterial crossing of the crucial intestinal barrier.</p> <br>

<p dir="ltr">The aquaculture industry has experienced remarkable expansion over the past few decades, largely due to the development of modern technologies and intensive farming systems. However, as the industry continues to grow, farming-related and environmental stressors such as overcrowding, poor water conditions and handling have continued to pose major obstacles to the worldwide expansion of this sector. The presence of these stressors affect the growth potential and health of farmed animals leading to significant economic losses. Hence, efficient management of the stress response of farmed species via sustainable means is important to ensure continuous development of the aquaculture sector. This study, therefore, explores the potential of dietary tryptophan supplementation to mitigate stress and improve growth, immune response, and disease resistance in channel catfish (<i>Ictalurus punctatus</i>). The study comprised a 36-day feeding trial where juvenile catfish were fed a tryptophan-supplemented diet under stressed (cortisol-supplemented) and unstressed conditions, followed by a 72-hour disease challenge with <i>Aeromonas hydrophila </i>(vAh). At the end of the study, the results show tryptophan supplementation did not significantly enhance growth or nutrient utilization, likely due to its neuroendocrine effects on feed intake. However, tryptophan demonstrated potential in modulating stress physiology and immune responses, including upregulation of key immune-related genes post-infection and promoting survival against vAh infection. These findings suggest that while tryptophan may not directly improve growth in our specific experimental conditions, its role in stress and immune regulation warrants further investigation, particularly in optimizing its dosage and combination with other dietary additives.</p>