Biosynthesis of silver nanoparticles synthesized from cell-free supernatant of Pediococcus acidilactici CE51 and assessment of their effect on Listeria monocytogenes biofilms

Listeria monocytogenes is the etiological agent of listeriosis, a severe disease with mortality rates of up to 30 %, particularly in immunocompromised individuals. Its ability to form biofilms in food processing environments hinders removal by conventional sanitizers, increasing the risk of contamination in ready-to-eat foods. This study aimed to synthesize silver nanoparticles (AgNPs) using cell-free supernatant (CFS) from Pediococcus acidilactici CE51 and evaluate their effectiveness against L. monocytogenes biofilms. Bac-AgNPs were characterized by dynamic light scattering, polydispersity index (PDI), zeta potential, UV–Vis spectrophotometry, and scanning electron microscopy. Bac-AgNPs (164 mg/mL) showed an average size of 131.8 ± 2.7 nm, PDI of 0.28 ± 0.02, zeta potential of −19.7 ± 0.6 mV, and a maximum absorbance peak at 420 nm. SEM revealed predominantly spherical nanoparticles. Toxicity assays in Galleria mellonella showed 100 % survival, while exposure to AgNO3 reduced larval survival by 40 % after 96 h. Against L. monocytogenes, Bac-AgNPs demonstrated a MIC of 82 mg/mL, MBC of 164 mg/mL, and promoted a 3.06 log CFU/mL reduction. Antimicrobial activity was preserved at pH 2 and 7, but declined at pH 9 and after 7 days of storage at 4 °C. In biofilm assays, Bac-AgNPs alone reduced bacterial counts by 2.5 log CFU/mL after 24 h, while the combination with CFS yielded reductions of up to 1.58 log CFU/mL at 1 h and 2.5 log CFU/mL at 24 h. These findings demonstrate that Bac-AgNPs synthesized using P. acidilactici CE51 possess promising antimicrobial and antibiofilm properties, good biocompatibility, and potential application in food safety, despite stability limitations.