Enzyme activated photodynamic therapy for methicillin-resistant Staphylococcus aureus infection both inv itro and in vivo

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) has become one of the most common multi-drug resistant bacteria in both hospital and community. The aim of this study is to investigate the selective inhibition of MRSA by a modified photosensitizer (LAEtNBS) in vitro and the efficacy of MRSA infection treatment by photodynamic therapy (PDT) with LAEtNBS in vivo . LAEtNBS was synthesized by adding a cationic photosensitizer molecule (EtNBS-COOH) and a quencher molecule to two side chains of cephalosporin , which was then shown to have similar absorption and emission wavelengths with EtNBS-COOH, but suppressed yields of fluorescence quantum and singlet oxygen . The selective inactivation and less phototoxicity of LAEtNBS, compared to that of EtNBS-COOH, were assessed and confirmed by conducting PDT to two Staphylococcus aureus strains and human skin cells at a fluence of 15   J/cm 2 with 640   ±   10   nm LED light. Furthermore, using mouse skin wound model infected with 10 8 CFU of MRSA, we found that both LAEtNBS and EtNBS-COOH were able to treat MRSA infection and enhance wound repair. However, there was no significant difference in the two photosensitizers that might be due to the environment in vivo . Modification of the photosensitizer will be very beneficial for developing new strategies to treat drug resistant bacterial infection with less harm to host tissue.