Choudhary, Ruplal, Department of Plant, Soil and Agricultural Systems, Southern Illinois University, Carbondale, USA

Curcumin has been known for a long time for its antimicrobial properties that are further increased by exposure to light. Due to the low aqueous solubility of curcumin, appropriate delivery systems are required to facilitate its implementation. In this work, we compared the antimicrobial activity toward Escherichia coli of two curcumin formulations: methyl-β-cyclodextrin supramolecular inclusion complex and polyelectrolyte-coated monolithic nanoparticles. The two formulations showed disparity both in the extent and in the mode of toxicity, highlighting the distinct properties of materials at the nanoscale. The tests showed that while curcumin–β-cyclodextrin complexes exhibited a potent bactericidal activity, the curcumin nanoparticles were bacteriostatic. Illumination with blue light significantly increased the bactericidal efficacy of curcumin–cyclodextrin complexes but had limited influence on the activity of nanoparticulate curcumin. While the antimicrobial effect of the supramolecular complex was predominantly characterized by the increase in ROS and inhibition of electron transport, the primary attributes of the nanoparticle action were membrane depolarization and reduced ATP concentrations. Interestingly, the treatment with curcumin nanoparticles induced a filamentous phenotype of the bacterium. Our results suggest that the antimicrobial properties of curcumin depend upon a delivery formulation, which may have both practical and regulatory implications on the applicability and safety of curcumin nanomaterials.