Lactobacillus casei expressing Internalins A and B reduces Listeria monocytogenes interaction with Caco-2 cells in vitro

Listeria monocytogenes has been implicated in a number of outbreaks including the recent largest outbreak in South Africa. Current methods for prevention of foodborne L. monocytogenes infection are inadequate, thus raising a need for an alternative strategy. Probiotic bioengineering is considered a prevailing approach to enhance the efficacy of probiotics for targeted control of pathogens. Here, the ability of Lactobacillus casei expressing the L. monocytogenes invasion proteins Internalins A and B (inlAB) to prevent infection was investigated. The inlAB operon was cloned and surface-expressed on L. casei resulting in a recombinant strain, Lbc(InlAB), and subsequently, its ability to inhibit adhesion, invasion and translocation of L. monocytogenes through enterocyte-like Caco-2 cells was examined. Cell surface expression of InlAB on the Lbc(InlAB) was confirmed by Western blotting and immunofluorescence staining. The Lbc(InlAB) strain showed significantly higher (P < 0.0001) adherence, invasion and translocation of Caco-2 cells than the wild-type L. casei strain (Lbc(WT)), as well as reduced L. monocytogenes adhesion, invasion and transcellular passage through the cell monolayer than Lbc(WT). Furthermore, pre-exposure of Caco-2 cells to Lbc(InlAB) significantly reduced L. monocytogenes-induced cell cytotoxicity and epithelial barrier dysfunction. These results suggest that InlAB-expressing L. casei could be a potential practical approach for prevention of listeriosis.