Discovery and Characterization of a Novel Bacteriocin PFS-3 Targeting Multidrug-Resistant Escherichia coli

The widespread use of commercial antibiotics has led to the emergence of multidrug resistance in pathogenic bacteria, posing a significant threat to human health and underscoring the urgent need for alternative antimicrobial agents. In this study, a bacteriocin-producing strain, Bacillus velezensis FS-3 (B. velezensis FS-3), was isolated from soil in Changbaishan, China. Fermentation conditions were optimized to enhance both bacteriocin activity and yield. A novel bacteriocin, PFS-3, was purified from B. velezensis FS-3 using hydrochloric acid precipitation, organic solvent extraction, and preparative reversed-phase high-performance liquid chromatography. Liquid chromatography-mass spectrometry/mass spectrometry analysis determined its molecular weight to be 929.16 Da, and amino acid sequencing of this peptide revealed eight amino acids (STYLFEGL). To date, the biological properties of PFS-3 have not been reported. We demonstrate here that PFS-3 exhibits low toxicity and remarkable stability under diverse conditions, including variations in temperature, pH, and the presence of metal ions or organic reagents. PFS-3 displayed broad-spectrum antimicrobial activity, with particularly strong activity against Gram-negative bacteria. Notably, its minimum inhibitory concentration against multidrug-resistant Escherichia coli B2 (MDR E. coli B2) was 16 μg/mL. Mechanistic investigations revealed that bacteriocin PFS-3 exerts bactericidal effects on MDR E. coli B2 by disrupting cardiolipin in the outer membrane of the cells. Furthermore, in vivo experiments demonstrated that PFS-3 significantly improved survival rates in infection models of MDR E. coli. In conclusion, PFS-3 is a newly identified bacteriocin with strong antibacterial activity, high stability, safety, and a favorable therapeutic index, highlighting its potential applications in the food industry and biopharmaceuticals for combating MDR E. coli infections.