Employment of mastoparan-like peptides to prevent Staphylococcus aureus associated with bovine mastitis

Bovine mastitis is a frequent infection in lactating cattle, causing great economic losses. Staphylococcus aureus represents the main etiological agent, which causes recurrent and persistent intramammary infections because conventional antibiotics are ineffective against it. Mastoparan-like peptides are multifunctional molecules with broad antimicrobial potential, constituting an attractive alternative. Nevertheless, their toxicity to host cells has hindered their therapeutic application. Previously, our group engineered three mastoparan-L analogs, namely mastoparan-MO, mastoparan-R1, and [I-5, R-8] MP, to improve cell selectivity and potential. Here, we were interested in comparing the antibacterial efficacy of mastoparan-L and its analogs against bovine mastitis isolates of S. aureus strains, making a correlation with the physicochemical properties and structural arrangement changes promoted by the sequence modifications. As a result, the analog's hemolytic and/or antimicrobial activity was balanced. All the peptides displayed alpha-helical folding in hydrophobic and membrane-mimetic environments, as determined by circular dichroism. The peptide [I-5, R-8] MP stood out for its enhanced selectivity and antibacterial features related to mastoparan-L and the other derivatives. Biophysical approaches revealed that [I-5, R-8] MP rapidly depolarizes the bacterial membrane of S. aureus, causing cell death by subsequent membrane disruption. Our results demonstrated that the [I-5, R-8] MP peptide could be a starting point for the development of peptide-based drugs for the treatment of bovine mastitis, with the advantage of no residue in milk, which would help reduce the use of classical antibiotics.