Curcumin loaded nanoparticles as efficient photoactive formulations against gram-positive and gram-negative bacteria.

The constant increase in multi-resistant bacterial strains and the decline in the number of newly approved antibiotics necessitate the development of alternative approaches to antibiotic treatment. In this study, a modern alternative approach to antibiotic therapy using photosensitiser encapsulated polymeric nanoparticles is presented. Cationic nanoparticles were prepared using a biodegradable and biocompatible polymer poly (lactic-co-glycolic acid), a stabiliser poly (vinyl alcohol) and chitosan. Dynamic light scattering and laser Doppler anemometry were used to determine particle size distribution and ζ-potential respectively. To quantify the antibacterial photodynamic effect of the nanoparticles, in vitro studies were performed using Staphylococcus saprophyticus subsp. bovis and Escherichia coli DH5 alpha to represent both a gram-positive as well as a gram-negative strain. It was demonstrated that the particle ζ-potential significantly influenced the antibacterial phototoxicity, gaining up to 3 log higher efficacy for chitosan coated nanoparticles. Furthermore, neither irradiation alone nor curcumin in absence of light led to a significant growth reduction, confirming the photodynamic effect of curcumin. Electron microscopy has been used to study the morphological characteristics of the nanoparticles as well as their interaction with bacteria and the changes of bacterial morphology and ultrastructure upon photodynamic treatment. An increased adherence of the chitosan modified nanoparticles to the bacteria and structural damage upon photodynamic treatment was clearly evident and confirmed the results from in vitro studies.