Surface-Associated Components of Probiotic Lactiplantibacillus plantarum Strains Contribute to EHEC Inhibition and Modulation of Intestinal Macrophage Responses

Lactiplantibacillus plantarum strains can protect against intestinal pathogens through direct antagonism and modulation of host immunity, although the bacterial components linking these activities remain poorly understood. Here, we investigated the contribution of surface-associated components to the interaction of L. plantarum with enterohemorrhagic Escherichia coli (EHEC) and intestinal macrophages. L. plantarum CRL681 (Lp681), CRL1506 (Lp1506), and an Lp1506 ΔdltD mutant defective in lipoteichoic acid D-alanylation were compared for aggregation, interaction with EHEC, and antagonistic activity. Lp681 exhibited the highest autoaggregation and coaggregation capacities and the strongest inhibition of EHEC, whereas Lp1506 ΔdltD showed reduced aggregation and no detectable antagonistic activity in coculture. Electron microscopy revealed close associations between Lp681 or Lp1506 and EHEC, accompanied by alterations in pathogen cell-envelope integrity. Removal of the LiCl-extractable surface fraction partially reduced Lp681-mediated inhibition, while the corresponding extracted fraction, enriched in surface-associated proteins, retained direct anti-EHEC activity. In intestinal macrophages challenged with enterotoxigenic E. coli (ETEC), viable Lp681 and LiCl-treated cells induced largely similar cytokine/chemokine gene-expression profiles, whereas the LiCl-extractable fraction retained independent immunomodulatory activity. The pre-exposure of EHEC to Lp681 surface proteins altered its subsequent interaction with macrophages, reducing TNF-α and MCP-1 expression while increasing IL-10 and IL-1β. These findings identify the Lp681 surface as a functional interface connecting pathogen antagonism and host immune modulation and suggest that surface-associated proteins can influence host responses both directly and indirectly through their interaction with the pathogen.