Membrane Vesicles from Lacticaseibacillus Casei BL23 Exhibit Antimicrobial Activity Against Escherichia coli and Immunostimulatory Effects on Human Peripheral Blood Mononuclear Cells.

Abstract

Probiotics are live microorganisms known for their health benefits; however, they may pose risks for immunocompromised individuals. This study explores the potential of postbiotics, specifically membrane vesicles (MVs) derived from Lacticaseibacillus casei BL23, as a safer alternative. MVs are isolated via ultracentrifugation (UC) followed by size exclusion chromatography (SEC), revealing a mean size of 178 nm and a concentration of 2.53×10¹¹ particles mL^-1, with moderate stability over four months at 4°C. Antimicrobial assays demonstrate that SEC-isolated MVs effectively inhibit the growth of Escherichia coli DH5α. Confocal laser scanning microscopy confirms the internalization of MVs by both E. coli and macrophages. Additionally, MV treatment elicits a significant immune response, marked by increased levels of pro-inflammatory cytokines (TNF-α, IL-6, IL-8, IL-1β) alongside IL-10 production in peripheral blood mononuclear cells. Importantly, cytotoxicity assays indicate that MVs are non-toxic to these cells and preserve epithelial barrier integrity in Caco-2 cell monolayers. MVs showed a trend towards extending lifespan in the Caenorhabditis elegans in vivo model upon infection with Pseudomonas aeruginosa. These findings underscore the dual-activity potential of L. casei BL23 MVs as effective tools for combating infections while enhancing immune function, offering a promising strategy to address antibiotic resistance.