The antimicrobial peptide C14R is active against all pathogenic species of the ESKAPE group

Here, we report the broad-spectrum antibacterial activity of the synthetic antimicrobial and pore-forming peptide C14R against all six ESKAPE species. Using a radial diffusion assay and resazurin-based viability testing, C14R exhibited potent bactericidal effect with minimum inhibitory concentrations (MICs), defined as the lowest concentration of an antimicrobial agent that completely inhibits visible growth of planktonic microorganisms, ranging from 3.4 µg/mL (Enterococcus faecium, vancomycin-resistant) to 45.2 µg/mL (Klebsiella quasipneumoniae, ESBL).

C14R also inhibited biofilm formation by Gram-positive pathogens, with minimum biofilm inhibitory concentrations (MBICs), referring to the minimal concentration required to prevent the development of biofilms, of 15.0 µg/mL (Staphylococcus aureus, MRSA) and 22.0 µg/mL (E. faecium, VRE), whereas Gram-negatives biofilms showed higher tolerance. Together, these findings demonstrate that C14R retains high activity against multidrug-resistant ESKAPE strains, highlighting its potential as a lead compound for the development of next-generation antimicrobial drugs to expand the portfolio of available antibiotics in the future to brace health systems for these emerging and severe infections.