Human breast milk-derived Limosilactobacillus fermentum strains modulate hBD-2 expression against Neisseria meningitidis infection through the TLR-2/p38-MAPK/NF-κB pathway.

Probiotics, particularly lactic acid bacteria (LAB), are known for their antimicrobial and immunomodulatory properties. This study aimed to isolate and characterize probiotic LAB strains from human breast milk and evaluate their therapeutic potential, particularly against Neisseria meningitidis. Among 113 isolates, five non-hemolytic Lactobacillus strains were identified, with Limosilactobacillus fermentum BM-18 and BM-103 demonstrating strong probiotic traits, including acid and bile tolerance, strong hydrophobicity, and notable auto-aggregation abilities and vigorous antibacterial activity against bacterial pathogens. Both strains adhered effectively to A549 epithelial cells without cytotoxic effects. The strains BM-18 and BM-103 demonstrated significant antagonistic activity against N. meningitidis, and showed effective co-aggregation. Importantly, BM-18 and BM-103 significantly reduced N. meningitidis-induced pro-inflammatory cytokines IL-6 and TNF-α and restored epithelial innate immune responses by upregulating the antimicrobial peptide hBD-2. Mechanistic analysis revealed that these effects were mediated via activation of the TLR-2/p38-MAPK/NF-κB signaling pathway, while N. meningitidis alone suppressed hBD-2 by activating the TLR-4/MyD88/A20 axis. These findings highlight the therapeutic potential of breast milk-derived L. fermentum strains as functional probiotic candidates capable of modulating host immunity and enhancing mucosal defense. Further in vivo and clinical studies are warranted to validate their efficacy and safety.