Biogenic-Synthesized Silver Nanoparticles Using the Ligilactobacillus salivarius KC27L Postbiotic: Antimicrobial, Anti-Biofilm, and Antioxidant Activity and Cytotoxic Effects.

This study aimed to synthesize silver nanoparticles (AgNPs) using the postbiotic of the Ligilactobacillus salivarius KC27L strain and evaluate their multifunctional biological properties. The use of L. salivarius, a probiotic bacterium known for its ability to produce a wide range of metabolites, plays a crucial role in this process by acting as a natural, eco-friendly reducing, and stabilizing agent during AgNP synthesis. This approach not only eliminates the need for hazardous chemicals typically used in nanoparticle synthesis but also enhances the biocompatibility and biological efficacy of the resulting nanoparticles. Synthesized AgNPs were analyzed by Fourier transform infrared spectroscopy, FTIR (metabolites of postbiotic); UV-vis (peak of 435 nm); scanning electron microscope, SEM; transmission electron microscopy, TEM (spherical shapes, sizes < 50 nm), energy-dispersive spectrometry, EDS (peak at 3 keV); and zeta potential (- 18.6 mV). These nanoparticles (0.156-40 mg/mL) were evaluated for the antimicrobial and anti-biofilm activities against Escherichia coli ATCC 11229, Pseudomonas aeruginosa ATCC 27853, Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 35984, and Streptococcus mutans ATCC 25175, and antioxidant activities using four different methods (2,2-diphenyl-1-picrylhydrazyl free radical scavenging, metal ion chelating, hydroxyl radical scavenging, and superoxide anion scavenging activities). Also, the cytotoxic activity was investigated against a normal cell line (L929) for 24, 48, and 72 h. At a concentration of 40 mg/mL, the AgNPs demonstrated the highest antimicrobial efficacy, with inhibition zones measured as 14.9 mm for P. aeruginosa, 9.5 mm for E. coli, 15.7 mm for S. epidermidis, and 12.9 mm for S. mutans. The AgNPs exhibited anti-biofilm activities against all Gram-positive and Gram-negative bacteria strains studied. According to the DPPH method, the highest antioxidant activity was determined at 40 mg/mL AgNP concentration (80.93%). AgNPs were found to have no toxic effect at low concentrations (0.39-25 µg/mL). Biogenic synthesized AgNPs could be used in biotechnological applications (biomaterials, health, environmental, etc.) with antibacterial, anti-biofilm, antioxidant, and nontoxic properties. However, further research is needed to understand the mechanisms of action of the particles fully.