Control of infection in wounds is critically important to avoid transition to sepsis; however, recent rise of drug-resistant bacteria makes it difficult. Thus, antimicrobial photodynamic therapy (APDT) has recently received considerable attention. In this study, we examined methylene blue (MB)-mediated photodynamic
inactivation of Psuedomonas aeruginosa in rat burned skin. Two days after infection, the wound surface was contacted with a MB solution at different concentrations, and thereafter the wound was irradiated
with cw 665-nm light at a constant power density of 250 mW/cm<sup>2</sup> for different time durations. We obtained a two orders of magnitude decrease in the number of bacteria by PDT with a 2-h contact of 0.5-mM MB solution and a illumination of 480 J/cm<sup>2</sup>, demonstrating the efficacy of PDT against infection with Ps. aeruginosa in burns.
To obtain efficient antibacterial photodynamic effect in traumatic injuries such as burns, depth-resolved
dosimetry of photosensitizer is required. In this study, we performed dual-wavelength photoacoustic (PA)
measurement for rat burned skins injected with a photosensitizer. As a photosensitizer, methylene blue
(MB) or porfimer sodium was injected into the subcutaneous tissue in rats with deep dermal burn. The
wound was irradiated with red (665 nm or 630 nm) pulsed light to excite photosensitizers and green (532
nm) pulsed light to excite blood in the tissue; the latter signal was used to eliminate blood-associated
component involved in the former signal. Acoustic attenuation was also compensated from the
photosensitizer-associated PA signals. These signal processing was effective to obtain high-contrast image
of a photosensitizer in the tissue. Behaviors of MB and porfimer sodium in the tissue were compared.