RESUMO
BACKGROUND AND OBJECTIVES: Control of burn wound infection is difficult due to the increase in drug-resistant bacteria and deteriorated immune responses. In this study, we examined the usefulness of methylene blue (MB)-mediated antimicrobial photodynamic therapy (aPDT) with illumination by a light-emitting diode (LED) array for controlling invasive infections from the wound to inside the body for rats with an extended deep burn infected with Pseudomonas aeruginosa. STUDY DESIGN/MATERIALS AND METHODS: An MB solution with the addition of ethanol, ethylene-diamine-tetra-acetic acid disodium salt, and dimethyl sulfoxide was used as a photosensitizer (PS). An extended deep burn was made on the dorsal skin in rats and the wounds were infected with P. aeruginosa. The rats were divided into three groups: control (no treatment; n = 14), PS mixture application alone (PS alone group; n = 10), and aPDT group (n = 14). For aPDT, after the PS mixture was applied onto the surface of infected wounds, the wounds were illuminated with a 665-nm LED array at an intensity of 45 mW/cm2 three times per treatment, with an illumination duration of 20 minutes and an interval of 10 minutes. The treatment was repeated each day for 7 consecutive days (day 0-day 6). Bacterial numbers on the wound surface and the weights and survival rates of the animals were evaluated daily. At the endpoints, bacterial numbers in the liver and blood were counted. Since the PS mixture showed high dark toxicity against P. aeruginosa in vitro, the influence of the PS mixture application onto healthy skin was also examined in vivo. RESULTS: Even in the aPDT group, rapid bacterial regrowth was observed on the wound surface after each day's treatment, but the geometric mean values of the bacterial numbers before and after each aPDT were considerably lower than those in the control group. Application of the PS mixture alone showed a clear bactericidal effect only at day 0, which is attributable to the formation of biofilms after day 1. Rats in the aPDT group showed a smaller weight loss, a higher ratio of no bacterial migration at the endpoints, and significantly higher survival rates than those in the other two groups. Effects of repeated application of the PS mixture onto healthy skin were not evident. CONCLUSIONS: Application of MB-mediated aPDT with illumination by a high-intensity LED array daily for seven consecutive days was effective for suppressing invasive infection from the wound to inside the body in rats with an extensive deep burn infected with P. aeruginosa, resulting in significant improvement of their survival. Lasers Surg. Med. © 2021 Wiley Periodicals LLC.