Recombinant Listeria adhesion protein expressing probiotics protect against Listeria monocytogenes infection in animal models

Listeria monocytogenes (Lm) is a foodborne pathogen, found ubiquitously in nature, and has a high morbidity rate among immunocompromised individuals, the elderly, and especially pregnant women and their fetuses resulting in abortion, stillbirth, and neonatal infection. There are currently no preventative medical interventions against Lm infection. The Listeria adhesion protein (LAP) is present in both pathogenic and non-pathogenic Listeria (i.e., L. innocua) and has shown to interact with host epithelial proteins causing tight junction dysregulation aiding in pathogen attachment and paracellular translocation across the host intestinal epithelium. Our lab has demonstrated that recombinant probiotics, Lactobacillus casei (LbcWT) expressing LAP from either the pathogenic L. monocytogenes (LbcLAPLm) or the nonpathogenic L. innocua (LbcLAPLin) prevented Lm attachment in in vitro cell culture experiments. Here, we investigated the beneficial attributes of our recombinant probiotics against clinical listerial infection of healthy mice and subclinical listerial infection in pregnant guinea pigs (GP). We supplied animals with freshly prepared wild type (LbcWT) and recombinant probiotics (9 × 10 9 cfu/ml) in sterile water daily for 10 (mice) or 17 days (GP). They were challenged with a clinical dose (4 × 108 cfu/mouse) and subclinical dose (9 × 108 or 4.5 × 10 9 cfu/GP) of Lm and sacrificed 48 h (mice) or 72 h (GP) post challenge. Organs, tissues, blood, feces and fetuses were collected for Lm presence and enumeration. Also, probiotic colonization, short chain fatty acid (SCFA), and serum cytokine, cholesterol, and trace mineral profiles were determined. Histopathological samples from the ileum, liver, and mesenteric lymph nodes (MLN) were scored for inflammation. Recombinant probiotics reduced Lm carriage in the challenged mice 3-5 log. In the recombinant probiotic-fed GP groups, Lm was present in the maternal liver, spleen, and MLN and absent in the maternal blood, kidney, placenta, and fetal liver, while LbcWT and Lm control groups showed Lm presence in nearly all tissues tested. We found no probiotic bacteria in any extra-intestinal tissues. Recombinant probiotic-fed groups showed a decrease in pro-inflammatory cytokines (TNFα, IL-6, TGFβ) in contrast to LbcWT and Lm control groups. Total SCFA content suggests that probiotics helped maintain SCFA levels against the detrimental effects of Lm. Among the trace minerals tested, serum calcium and zinc levels were higher (P \u3c 0.05) in recombinant probiotic-fed groups than the LbcWT and Lm control groups. Taken together, these data indicate that LAP-expressing recombinant probiotics confer anti-listerial effects, participate in immune modulation and have a positive impact on overall health in mice and pregnant guinea pigs. Due to the aforementioned high mortality rate among a significant portion of the population, these recombinant probiotics could confer protection against Lm and provide a platform for future research into the use of probiotics as a “probiotic vaccine