Biosynthesis and Characterization of Bacteriocin-Capped Silver Nanoparticles and Their Antimicrobial Activity Against Pathogenic Bacteria

Antimicrobial resistance is an escalating global concern. Bacteriocins are promising antimicrobial peptides but are limited by proteolytic degradation and a narrow spectrum of activity. Conjugation of bacteriocins with silver nanoparticles (SNPs) can protect peptides and provide synergistic antimicrobial activity. This study reports the biosynthesis, optimization, physicochemical characterization and antibacterial evaluation of crude bacteriocin from Lactiplantibacillus plantarum strains T4 and B2, and commercially purified nisin, used to cap silver nanoparticles (Bac-SNPs and Nisin-SNPs). Optimal Bac-SNPs synthesis was achieved at Bacteriocin:AgNO₃ = 1:9 (v/v), 65°C and pH 11. UV-Vis spectroscopy showed surface plasmon resonance peaks between 400–500 nm, confirming SNPs formation. FTIR spectra indicated hydroxyl and carboxyl functional groups involved in capping. Dynamic light scattering revealed Z-average sizes of 63.14 nm (T4Bac-SNPs) and 80.65 nm (B2Bac-SNPs) with low polydispersity (PDI 0.260 and 0.263), whereas Nisin-SNPs exhibited larger hydrodynamic size (≈458 nm) and higher PDI (0.434), consistent with different capping behaviour. Antimicrobial evaluation demonstrated that Nisin-SNPs enhanced the activity of purified nisin against all tested pathogens (Listeria monocytogenes, Bacillus cereus and Escherichia coli), with the most prominent inhibition observed against E. coli (18.00 ± 0.00 mm). In contrast, Bac-SNPs derived from strains T4 and B2 showed lower or comparable inhibition zones relative to their corresponding crude bacteriocins, indicating that nanoparticles conjugation did not uniformly enhance antibacterial activity. Overall, the findings demonstrate that bacteriocin type and synthesis conditions critically influence the physicochemical properties and antibacterial performance of bacteriocin-capped silver nanoparticles.