Development and Biological Evaluation of FL18-Based Novel Antimicrobial Peptide Constructs Against Bacterial Pathogens.

Antimicrobial resistance has become a serious global health challenge, increasing the need for new therapeutic strategies beyond conventional antibiotics. In this study, FL18 and its chimeric derivatives, FL18-TAT8 and FL18-Ahx-TAT8, were designed to combine antimicrobial activity with the cell-associated advantages of a cell-penetrating peptide motif and were synthesized by Fmoc-based solid-phase peptide synthesis. Their molecular masses were confirmed by MALDI-MS analysis. The antibacterial activities of the peptides were evaluated against representative Gram-negative and Gram-positive bacterial strains, including Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecium. The tested peptides exhibited minimum inhibitory concentration values in the range of 4-64 μM depending on the peptide sequence and bacterial strain, while TAT8 alone showed no significant antibacterial activity under the tested conditions. Among the constructs, FL18-Ahx-TAT8 displayed the most favorable overall antibacterial profile, particularly against P. aeruginosa and E. faecium. Biocompatibility studies further showed that FL18 and its chimeric derivatives maintained approximately 75-90% HaCaT cell viability across the tested concentration range and exhibited generally low hemolytic activity. In addition, confocal microscopy and flow cytometry revealed peptide-associated fluorescence in HaCaT cells, with the TAT8-containing chimeras showing a broader and more pronounced fluorescence distribution than FL18 alone. Overall, these findings demonstrate that FL18-based chimerization provides a modular and effective strategy for tuning antibacterial activity, biocompatibility, and peptide-cell interaction behavior, underscoring their promise as building blocks for the design of next-generation antimicrobial peptide platforms.