The discovery of novel antimicrobial peptides against multidrug-resistant bacteria based on thioether cyclization and unnatural amino acid incorporation strategies.

The rise of multidrug-resistant (MDR) bacterial infections highlights the urgent need for novel antimicrobial agents. Previously, we designed a hybrid peptide 13D, by fusing fragments of sC184b (1-9) and MSI-78 (10-13). Although 13D exhibited potent activity against clinically isolated MDR bacteria, its physiological stability remains to be further enhanced. In this study, we rationally truncated the 13D sequence, employed a xylene-based double thioether bridge for cyclization and introduced non-natural amino acids to generate a series of cyclic peptides. Among these, P10 showed broad-spectrum activity against MDR pathogens via a membrane-disruptive mechanism, together with superior stability in serum, trypsin and chymotrypsin, and reduced cytotoxicity compared with 13D. Importantly, P10 achieved significant therapeutic efficacy in a murine model of acute peritonitis induced by MDR P. aeruginosa. These findings suggest that P10 is a promising therapeutic candidate against MDR bacterial infections.