From phytochemical capping to microbial disruption: Mechanistic evaluation of saffron-mediated silver nanoparticles against bacterial growth and biofilm formation

The recent attractiveness of green-synthesized silver nanoparticles (AgNPs) stems from their ability to couple strong antimicrobial efficacy with the surface functionalization by phytochemicals, which makes them promising for the effective control of microbial growth and biofilms. This work involves green synthesis of AgNPs using Crocus sativus stigma, yielding nanoparticles characterized by stable nanoscale dimensions, high crystallinity, good colloidal stability and saffron phytochemicals as surface functionalization. The synthesized AgNPs had significant concentration dependent antibacterial activity against both S. aureus and E. coli . As the concentration of nanoparticles increased, the inhibition zones grew larger for both S. aureus (from 7 to 16 mm) and E. coli (from 7 to 20 mm). Complete bacterial growth inhibition was achieved at MIC values of 31.25 and 62.5 μg/mL for S. aureus and E. coli respectively. Interestingly, the MBC values were consistent with the corresponding MIC values for both bacterial strains, supporting a bactericidal effect of the synthesized AgNPs at their respective MIC concentrations. Besides, the biosynthesised AgNPs significantly inhibited the biofilm formation by lowering its biomass from 0.90 to 0.10 for S. aureus and 0.85–0.15 at the highest tested concentration for E. coli . In summary, all these results confirm the antibacterial and antibiofilm properties of saffron-mediated AgNPs, which are potentially due to the contribution of nanoscale dimensions, nanocrystalline structure, nanocolloidal stability, nanoroughness, and phytochemical capping. The study thus proposes a mechanistic connection between the physicochemical properties of nanoparticles and microbial disruption which might allow the use of these nanomaterials as multifunctional antimicrobial agents.