Photodynamic inactivation against Pseudomonas aeruginosa by curcumin microemulsions†
Curcumin is a polyphenol compound extracted from the rhizomes of Curcuma longa. This natural dye can react with the surrounding oxygen and matrix to generate singlet oxygen and reactive oxygen species. This observed effect can be utilized in combination with blue light to exert bactericidal action. However, aggregation due to curcumin's low water solubility limits its photodynamic applications. In this study, Pseudomonas aeruginosa was chosen to evaluate the photodynamic effect of curcumin by using the blue light diode. A thermodynamically stable microemulsion was adopted as the vehicle to encapsulate curcumin with the help of the pseudo-ternary phase diagram. The microemulsion, composed of Tween 80, propylene glycol, water, and geraniol, could homogeneously disperse curcumin and stabilized the photosensitizer. Dynamic light scattering analysis and encapsulation efficiency results showed that the developed microemulsion had a 130 nm size and a 96% payload. In ex vivo tests, microemulsion could remain the curcumin in the stratum corneum and would not cause damage to dermal tissue. Photodynamic testing against planktonic and biofilm bacteria showed that the curcumin microemulsion displayed increased inhibition to P. aeruginosa. When combined with ethylenediamine tetraacetic acid, the curcumin microemulsion completely eliminated the bacterial population under light-irradiation. Scanning electron microscopic images indicated damage in bacterial morphology after photodynamic treatment. Our results demonstrate that a curcumin microemulsion combined with photodynamic inactivation could be a facile approach to control the proliferation of P. aeruginosa on the skin.