Improved Photodynamic Inactivation of Gram-Positive Bacteria Using Hematoporphyrin Encapsulated in Liposomes and Micelles

Background and Objectives: Antimicrobial photodynamic inactivation (PDI) is a promising treatment modality for local infections. To increase the efficacy of photosensitizer, hematoporphyrin (Hp) was used as a model drug and encapsulated in liposomes and micelles. The bactericidal efficacy of the carrier-entrapped Hp was assessed against gram-positive bacteria. Study Design/Materials and Methods: Hp was encapsulated in liposomes by a modified reversed-phase evaporation and extrusion method. Micelle-Hp was prepared by the reversed-phase evaporation method. Spectroscopic analysis was used to characterize the properties of Hp in PBS, liposome or micelle. The PDI efficacy was examined by using gram-positive pathogens including methicillin-susceptible, methicillin-resistant Staphylococcus aureus, Staphylococcus epidermidis, and Streptococcus pyogenes. Results: The absorption and fluorescence emission spectra indicated that Hp encapsulated in liposomes and micelles is less likely to exist in aggregated form compared to that generally seen in an aqueous medium. Liposome- or micelle-Hp can induce complete eradication of the bacteria above a critical Hp dose, which is significantly lower than the dose required when using the non-encapsulated Hp. Furthermore, the PDI effect of the Hp encapsulated in micelles was superior to the Hp encapsulated in liposomes at lower Hp doses. Similar PDI results were also found in S. epidermidis and S. pyogenes. Conclusions: Our results indicate that photosensitizer entrapped in micelle exert similar or better PDI efficacy than that of liposome, which indicates this formulation may be useful for the treatment of local infections in the future. Lasers Surg. Med. 41:316-322, 2009. (C) 2009 Wiley-Liss, Inc.