Microbial synthesis of silver nanoparticles using bacterial supernatants from Brazilian stingless bees with antimicrobial activity

The increasing prevalence of antibiotic-resistant bacteria poses a significant global public health challenge, particularly with multidrug-resistant pathogens such as Staphylococcus aureus and Escherichia coli. In this context, silver nanoparticles (AgNPs) have garnered attention as promising alternative antimicrobial materials due to their unique physicochemical properties. In this study, we investigated the green synthesis of AgNPs using bacterial supernatants derived from the larval food of Brazilian stingless bees, a biologically rich and underexplored source of functional metabolites. Using supernatants of Providencia rettgeri and Proteus mirabilis, AgNPs were synthesized via both traditional and microwave-assisted methods, with the latter promoting faster nanoparticle formation and improved colloidal homogeneity. Two AgNP formulations (AgNPs-1B and AgNPs-54B), selected for their distinct synthesis profiles, were characterized by UV-visible spectroscopy, dynamic light scattering, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and transmission electron microscopy (TEM). TEM analysis revealed predominantly spherical nanoparticles, with average diameters of 24.2 ± 27.4 nm for AgNPs-1B and 8.5-25.2 nm for AgNPs-54B, confirming successful nanoscale synthesis. Both AgNPs exhibited significant antimicrobial activity against multidrug-resistant E. coli and S. aureus. When incorporated into alginate-based membranes, the nanoparticles retained their antimicrobial efficacy, particularly through contact-dependent inhibition of bacterial growth. Toxicity assays using Drosophila melanogaster and human neuron cultures indicated low toxicity in the evaluated biological models. These findings demonstrate the potential of biologically synthesized AgNPs as sustainable antimicrobial materials, combining a unique microbial source with microwave-assisted processing and relevant biomedical and environmental applicability.