Postbiotin-E8, a Novel Antimicrobial Postbiotic Peptide from Lacticaseibacillus sp. E8: Antibacterial, Antibiofilm and Food Preservation Potential

The increasing prevalence of antimicrobial resistance has intensified the search for stable bio-based antimicrobial agents for food and therapeutic applications. In this study, a novel proteinaceous postbiotic peptide, designated Postbiotin-E8, was isolated from an environmental Lacticaseibacillus sp. E8 strain. Sequential purification using ethanol precipitation, cation-exchange chromatography and RP-HPLC resulted in a 4.15-fold increase in specific activity with 29% recovery. Tricine-SDS-PAGE, MALDI-TOF, and LC-MS analyses confirmed a homogeneous peptide with a molecular mass of approximately 3.75 kDa. N-terminal sequencing identified a unique 33-amino-acid sequence enriched in hydrophobic and cationic residues, consistent with an amphipathic antimicrobial peptide. Postbiotin-E8 exhibited substantial physicochemical stability, retaining antimicrobial activity across a broad pH range (4–8), moderate thermal conditions (up to 50°C), and in the presence of selected detergents and organic solvents. The peptide demonstrated broad-spectrum antibacterial activity against Escherichia coli, Bacillus cereus, Staphylococcus aureus, and Salmonella Typhi. Growth inhibition, bactericidal activity after 24 h exposure, and antibiofilm assays demonstrated concentration-dependent antibacterial activity and effective inhibition of biofilm formation against S. aureus and S. Typhi . Furthermore, Postbiotin-E8 improved the microbiological, physicochemical, visual and sensory stability of refrigerated milk, indicating its potential as a natural bio-preservative. These findings identify Postbiotin-E8 as a structurally distinct antimicrobial peptide with potential applications in food biopreservation, surface decontamination and future therapeutic interventions.