Combinatorial Effects of CPP-Modified Antimicrobial Peptides: Synergistic and Additive Interactions Against Pathogenic Bacteria

The development of novel antimicrobial peptides (AMPs) with broad-spectrum activity represents a promising strategy to overcome multidrug resistance in pathogenic bacteria. In this study, we investigated the antimicrobial activity of three designed peptides-R44K^S*, V31K^S*, and R23F^S*-engineered to incorporate an amyloidogenic fragment from the S1 protein of <i>Staphylococcus aureus</i> and one or two cell-penetrating peptide (CPP) fragments to enhance cellular uptake. The antimicrobial efficacy of these peptides and their combinations was assessed against <i>Pseudomonas aeruginosa</i>, <i>Escherichia coli</i>, <i>Staphylococcus aureus</i>, methicillin-resistant <i>S. aureus</i> (MRSA), and <i>Bacillus cereus</i>. The results demonstrated that all three peptides exhibited significant antibacterial activity in a concentration-dependent manner, with R44K^S* being the most potent. Peptide combinations, particularly V31K^S*/R23F^S* and R44K^S*/V31K^S*, showed enhanced inhibitory effects and reduced minimum inhibitory concentrations (MICs), suggesting synergistic or additive interactions. Fractional inhibitory concentration index (FICI) analysis confirmed that most combinations exhibited synergy or additive effects. These findings highlight the potential of CPP-modified peptides as antimicrobial agents and underscore the importance of optimizing peptide combinations for therapeutic applications.