Antibacterial function and mechanism of peptide β-casein 65 action in breast milk

Breast milk has significant benefits to preterm infants, including reduced risk of infection and inflammatory disorders. Many biomolecules, such as peptides, that exhibit immunomodulation function or antimicrobial activity and protect against infection have been identified in human milk. β-Casein 65, an endogenous peptide cleaved amino acids 204-225 of β-casein, is expressed at high levels in preterm breast milk. Our study demonstrates the antibacterial activity of β-casein 65 against Staphylococcus aureus ( S. aureus ) and Escherichia coli ( E. coli ) through use of an agarose filter paper diffusion and microdilution method. The LIVE/DEAD BacLight bacterial viability assay results also confirmed the antibacterial effects of β-casein 65. Destroyed membrane structures in S. aureus and E. coli after treatment with β-casein 65 were observed by scanning electron microscopy and transmission electron microscopy. A DNA-binding assay showed that β-casein 65 exerts antimicrobial effects independent of DNA-binding activity. Our results revealed the antibacterial activity and mechanism of peptide β-casein 65 sourced from human milk. Further studies should be carried out to determine ways to prevent and treat pathogens in animals and human neonates.