An amphipathic peptide combats multidrug-resistant Staphylococcus aureus and biofilms

The emergence of drug-resistant Staphylococcus aureus (S. aureus) has resulted in infections in humans and animals that may lead to a crisis in the absence of highly effective drugs. Consequently, the development of alternative or complementary antimicrobial agents is urgently needed. Here, a series of peptides derived from AP138 were designed with high expression, antimicrobial activity, and antibiofilm properties via bioinformatics. Among them, the best derived peptide, A24 (S9A), demonstrated the greatest stability and bactericidal efficiency against multidrug-resistant S. aureus in a physiological environment, with a high hydrophobicity of 35%. This peptide exhibited superior performance compared to the preclinical or clinical antimicrobial peptides (AMPs). A24 displayed increased biocompatibility in vitro and in vivo, exhibiting a low hemolysis rate (less than 3%), minimal cytotoxicity (survival rate exceeding 85%), and no histotoxicity. A24 had the capacity to destroy cell walls, increase cell membrane permeability, and induce increases in intracellular ATP and ROS levels, which resulted in the rapid death of S. aureus. A24 inhibited the formation of early biofilms and eliminated both mature biofilms (40-50%) and persisters (99.9%). Therapeutic doses of A24 were shown to exhibit favorable safety profiles and bactericidal efficacy in vivo and could reduce bacterial loads of multidrug-resistant S. aureus by 4-5 log₁₀ CFU/0.1g levels in mouse peritonitis and endometritis models. Furthermore, A24 increased the survival rate to 100% and exhibited anti-inflammatory properties in a mouse model. The aforementioned data illustrate the potential of A24 as a pharmaceutical agent for the treatment of bacterial infections, including peritonitis and endometritis, in animal husbandry with multidrug-resistant S. aureus infections.