Purpose: In this study, we synthesized a series of silver-iron nanoparticles via co-precipitation method and evaluated their antibacterial activity against pathogens commonly associated with food and water borne infections.
Methods: Different combinations of silver- iron nanomaterials (Ag-Fe NPs) were synthesized via co-precipitation method and characterized by Powder X-ray Diffraction (PXRD), Fourier Transform Infrared (FTIR) Spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), UV spectroscopy and magnetic studies. Microplate broth-dilution assays alongwith CFU plate count, vital staining and epi-fluorescence microscopy, were used to perform time-kinetics, MIC, recycling studies and in situ killing of bacteria within food matrices. Bacterial interactions with NPs were further confirmed by TEM.
Results: The synthetic Ag-Fe NPs were super-paramagnetic, ~ 30 nm in size, spherical with protruding ends. Short time exposure of bacterial cultures to NPs captured viable bacteria within 2 minutes while extended incubation exhibited a broad spectrum of antimicrobial activity against both gram-positive and gram-negative bacteria with MIC90 at 60 and 30 minutes of incubation, respectively. The MIC90 of Ag-Fe NPs against B. subtilis and E. coli was found to be 2.4 and 20 µg/ml, respectively. In situ killing by Ag-Fe NPs in water, milk and juice samples showed 97%, 49% and 4% killing of B. subtilis and E. coli, respectively. Recycling of Ag-Fe NP over 3 subsequent rounds retained the antimicrobial activity.
Significance: These studies suggest Ag-Fe NPs as a promising template for designing novel antibacterial agents that rapidly and repeatedly capture and kill pathogens from biological matrices at low concentrations.