Abstract: In this research, to investigate the antibacterial mechanism of a novel casein-derived antibacterial peptide, BCp12, against Staphylococcus aureus, the mechanism of cell membrane and wall damage caused by BCp12 was analyzed using a microplate reader (MR), a flow cytometer (FC), and a transmission electron microscope (TEM). The effects of BCp12 on DNA binding and protein synthesis were studied using fluorescence spectroscopy and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The influence of BCp12 on protein post-translational modification (PTM) was analyzed by Western blot using pan anti-acetyl, anti-succinyl, anti-2-hydroxyisobutyryl and anti-malonyl lysine antibodies. The results showed that the minimum inhibitory concentration (MIC) of BCp12 was 2 mg/mL. Treatment with BCp12 at concentrations above the MIC decreased the cell surface hydrophobicity of S. aureus significantly (P ≤ 0.001), increased the cell membrane permeability, and caused the cells to deform severely and cellular contents leak out to form a cavity. BCp12 competed with ethidium bromide to combine with bacterial DNA, resulting in inhibition of nucleic acid synthesis and significantly decreased protein contents (P ≤ 0.001), especially for proteins with a molecular mass of 15–35 kDa, indicating that BCp12 can inhibit the synthesis of bacterial proteins. S. aureus proteins showed a large number of lysine acetylation, succinylation and malonylation. The level of malonylation was significantly down-regulated after treatment with BCp12, which, however, had no noticeable effect on the level of 2-hydroxyisobutyrylation or succinylation. The results of this study are meaningful for applying new milk-derived antimicrobial peptides and ensuring food safety.

Key words: antimicrobial peptide BCp12; Staphylococcus aureus; wall and membrane damage; protein synthesis; malonylation