Abstract
.SignificancePseudomonas (P.) aeruginosa, a common cause of infection in burns, acquires antibiotic resistance easily and forms biofilms efficiently. Thus, it is difficult to control P. aeruginosa infection in burn wounds, which causes lethal septicemia. Antimicrobial photodynamic therapy (aPDT) is attractive as a new strategy to treat burn wound infections with drug-resistant bacteria.AimWe examined the efficacy of methylene blue (MB)-mediated aPDT with various additives in a tissue depth-resolved manner to find conditions that minimize the bacterial invasion.ApproachWe applied MB-mediated aPDT with LED array illumination to an extensive, full-thickness burn infected with P. aeruginosa in rats for three consecutive days (days 0, 1, and 2). On day 2, the depth distributions of bacteria were assessed based on the histological analysis using Gram staining. We examined how the addition of ethylenediaminetetraacetic acid (EDTA), ethanol, and dimethyl sulfoxide (DMSO) affected the efficacy of aPDT.ResultsPure MB-mediated aPDT significantly reduced the numbers of bacteria with biofilms on the wound surface and in the epidermis compared with those for the control tissue (saline only). However, there were many bacteria in the deeper region of the tissue. In contrast, MB/EDTA/ethanol/DMSO-mediated aPDT minimized the numbers of bacteria in the broad depth region of the tissue. Still, a limited number of bacteria was observed in the subcutaneous tissue.ConclusionsThe depthwise analysis of bacteria demonstrated the efficacy of the MB-mediated aPDT with the addition of EDTA, ethanol, and DMSO in controlling burn wound infections. However, further improvement of the therapy is needed to suppress bacterial migration into the deep tissue completely.
Highlights
Patients with severe burns have a higher susceptibility to infections due to the destruction of their cutaneous barrier and altered systemic immune responses.[1]
We previously found that methylene blue (MB)-mediated Antimicrobial photodynamic therapy (aPDT) with the addition of ethylenediaminetetraacetic acid (EDTA), ethanol, and dimethyl sulfoxide (DMSO) was effective for controlling P. aeruginosa infections in a rat extended, full-thickness burn model.[5]
The bactericidal effects of the treatments on day 1 were different depending on the groups; CFU reductions were 1.6 log[10] for aPDT with only MB (aPDT I) (MB only), 3.4 log[10] for aPDT II (MB/ethanol/EDTA), and 4.2 log[10] for aPDT III (MB/ethanol/EDTA/DMSO)
Summary
Patients with severe burns have a higher susceptibility to infections due to the destruction of their cutaneous barrier and altered systemic immune responses.[1]. Antimicrobial photodynamic therapy (aPDT) is an attractive treatment strategy for burn wound infections with drug-resistant bacteria.[4] In aPDT, a photosensitizer (PS) is excited by light, and the excited energy is transferred to the oxygen in tissues, producing reactive oxygen species (ROS), such as singlet oxygen. We previously found that methylene blue (MB)-mediated aPDT with the addition of ethylenediaminetetraacetic acid (EDTA), ethanol, and dimethyl sulfoxide (DMSO) was effective for controlling P. aeruginosa infections in a rat extended, full-thickness burn model.[5] EDTA, ethanol, and DMSO play a role in suppressing biofilm formation, increasing singlet oxygen productivity, and enhancing drug delivery into the tissue, respectively.[6,7,8,9] Still, we observed rapid bacterial regrowth on the wound surface even after a daily application of aPDT for a week, suggesting a powerful invasion of residual bacteria into the deeper tissue. To the best of knowledge, there are no reports on the depth-resolved analysis of the aPDT efficacy in tissues
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