Hydrogen peroxide as an additive to curcumin on the photodynamic inactivation of bacteria: a preliminary study

Photodynamic inactivation (PDI) of microorganisms has been shown as a promising alternative against the spread of resistant bacteria. It has been used not only in clinical applications, but also in the public health sector, for water and wastewater disinfection. In order to improve efficiency, recent research has focused on novel photosensitizing materials, as well as chemical additives. To our knowledge, however, hydrogen peroxide (a widely known standalone disinfectant) has not been employed combined with curcumin (a vegetal-based and environmental-friendly photosensitizer) for PDI seeking for future environmental applications. In this sense, this study aimed to assess whether there were any competitive or cooperative effects by the simultaneous use of curcumin and hydrogen peroxide on the PDI of Staphylococcus aureus, in in-vitro batch tests. Photobleaching for individual and combined factors was performed in order to compare results of inactivation with changes in chemical aspects in solution under blue light irradiation. One may think that the combination may add strength to PDI due to hydrogen peroxide being a natural supplier of oxygen. However, antagonistic effects were found in combined treatments, implying that such combination is non profitable. The results indicate that special care is necessary when considering combining techniques.