Bacitracin and isothiocyanate functionalized silver nanoparticles for synergistic and broad spectrum antibacterial and antibiofilm activity with selective toxicity to bacteria over mammalian cells

Silver nanoparticles functionalized with bacitracin (BA), a cyclic peptide and isothiocyanate (ITC), a natural plant product, was fabricated. The particle size of AgNP-BA&ITC was optimized using full factorial design. The optimized particles were of 10-15 nm in size as seen under TEM and showed chemical signature of both bacitracin as well as isothiocynate in FTIR spectroscopy. XRD analysis confirmed the crystalline nature of these particles. Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) showed 21 mg/g silver content in AgNP-BA &ITC. These nanoparticles exhibited MIC in the range of 12.5-25 μg/mL and > 3 log10 reduction in cell viability for both Gram positive and Gram-negative bacteria. They clearly demonstrated biofilm inhibition (BIC90 = 150-400 μg/mL) as well as were capable of eradicating both young and mature preformed biofilms as observed by live/dead imaging and crystal violet assay. Further cytotoxicity assay suggests high selectivity (IC50/MIC90 value = 15.2-30.4) of these particles. The results in the present investigation provide role of these novel nanoparticles having substantially low silver content with reduced toxicity and good antibacterial and antibiofilm activity for external wound healing applications.