Photosensitizer-loaded hydrogels for photodynamic inactivation of multirestistant bacteria in wounds.

Photodynamic treatment is a promising tool for the therapy of multidrug-resistant bacteria. In this study, we highlight photosensitizer-loaded hydrogels as an application system for infected wounds. The poly(ethylene glycol) diacrylate-based and electron beam-polymerized hydrogels were mechanically stable and transparent. They were loaded with two photoactive, porphyrin-based drugs - tetrakis(1 methylpyridinium-4-yl)porphyrin p -toluenesulfonate (TMPyP) and tetrahydroporphyrin - p toluenesulfonate (THPTS). The hydrogels released a sufficient amount of the photosensitizers (up to 300 μmol l -1 ), relevant for efficiency. The antimicrobial effectivity of loaded hydrogels was investigated in a tissue-like system as well as in a liquid system against a multiresistant Escherichia coli . In both systems, light induced eradication was possible. In contrast, hydrogels alone showed only minor antimicrobial activity. Furthermore, the loaded hydrogels were successfully tested against seven multidrug-resistant bacterial strains, namely Enterococcus faecium , Staphylococcus aureus , Klebsiella pneumonia , Acinetobacter baumannii , Pseudomonas aeruginosa , Escherichia coli and Achromobacter xylosoxidans . The eradication of these pathogens, except A. xylosoxidans , was successfully demonstrated. In general, TMPyP-loaded hydrogels were more effective than THPTS-loaded ones. Nevertheless, both photosensitizers displayed effectivity against all investigated bacteria strains. Taken together, our data demonstrate that photosensitizer-loaded hydrogels are a promising new tool to improve the treatment of wounds infected with problematic bacterial pathogens.