Protease Stabilizing Antimicrobial Peptide D1018M Showed Potent Antibiofilm and Anti-Intracellular Bacteria Activity Against MRSA

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) poses a major threat to human health and food safety, especially when bacteria form biofilms or invade host cells, which may cause recurring infections. A new solution is therefore urgently needed. The antimicrobial peptide innate defense regulator (IDR)-1018 and its derived peptide 1018M showed promising antimicrobial and antibiofilm activities. Nevertheless, their antibacterial efficacy against intracellular MRSA and protease tolerance remains to be promoted. Therefore, we synthesized D-amino acid substitution peptides D1018 and D1018M. The antimicrobial activity against MRSA of these novel peptides was increased by 1-fold (D1018) or remained constant (D1018M) compared with L-amino acids peptides. Their bactericidal mechanisms involve cell wall destruction, membrane penetration, and genomic DNA disruption. As expected, the stability of D1018 and D1018M was increased by 2-32 times against pepsin, trypsin, and cathepsin K. In addition, by D-amino acids substitution, the antibiofilm ability of D1018 was increased by 1.6 times, and the anti-intracellular bacterial activity of D1018M was improved 3.2-5.7 orders of magnitude. These data indicated that D1018M is a potential antimicrobial candidate for recurring MRSA infections.