Antimicrobial blue light therapy for multidrug-resistant Acinetobacter baumannii infection in a mouse burn model: implications for prophylaxis and treatment of combat-related wound infections.

In this study, we investigated the utility of antimicrobial blue light therapy for multidrug-resistant Acinetobacter baumannii infection in a mouse burn model. A bioluminescent clinical isolate of multidrug-resistant A. baumannii was obtained. The susceptibility of A. baumannii to blue light (415 nm)-inactivation was compared in vitro to that of human keratinocytes. Repeated cycles of sublethal inactivation of bacterial by blue light were performed to investigate the potential resistance development of A. baumannii to blue light. A mouse model of third degree burn infected with A. baumannii was developed. A single exposure of blue light was initiated 30 minutes after bacterial inoculation to inactivate A. baumannii in mouse burns. It was found that the multidrug-resistant A. baumannii strain was significantly more susceptible than keratinocytes to blue light inactivation. Transmission electron microscopy revealed blue light-induced ultrastructural damage in A. baumannii cells. Fluorescence spectroscopy suggested that endogenous porphyrins exist in A. baumannii cells. Blue light at an exposure of 55.8 J/cm(2) significantly reduced the bacterial burden in mouse burns. No resistance development to blue light inactivation was observed in A. baumannii after 10 cycles of sublethal inactivation of bacteria. No significant DNA damage was detected in mouse skin by means of a skin TUNEL assay after a blue light exposure of 195 J/cm(2).

Blue light eliminates community-acquired methicillin-resistant Staphylococcus aureus in infected mouse skin abrasions.

BACKGROUND AND OBJECTIVE: Bacterial skin and soft tissue infections (SSTI) affect millions of individuals annually in the United States. Treatment of SSTI has been significantly complicated by the increasing emergence of community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) strains. The objective of this study was to demonstrate the efficacy of blue light (415 ± 10 nm) therapy for eliminating CA-MRSA infections in skin abrasions of mice. METHODS: The susceptibilities of a CA-MRSA strain (USA300LAC) and human keratinocytes (HaCaT) to blue light inactivation were compared by in vitro culture studies. A mouse model of skin abrasion infection was developed using bioluminescent USA300LAC::lux. Blue light was delivered to the infected mouse skin abrasions at 30 min (acute) and 24 h (established) after the bacterial inoculation. Bioluminescence imaging was used to monitor in real time the extent of infection in mice. RESULTS: USA300LAC was much more susceptible to blue light inactivation than HaCaT cells (p=0.038). Approximately 4.75-log10 bacterial inactivation was achieved after 170 J/cm(2) blue light had been delivered, but only 0.29 log10 loss of viability in HaCaT cells was observed. Transmission electron microscopy imaging of USA300LAC cells exposed to blue light exhibited disruption of the cytoplasmic content, disruption of cell walls, and cell debris. In vivo studies showed that blue light rapidly reduced the bacterial burden in both acute and established CA-MRSA infections. More than 2-log10 reduction of bacterial luminescence in the mouse skin abrasions was achieved when 41.4 (day 0) and 108 J/cm(2) (day 1) blue light had been delivered. Bacterial regrowth was observed in the mouse wounds at 24 h after the blue light therapy. CONCLUSIONS: There exists a therapeutic window of blue light for bacterial infections where bacteria are selectively inactivated by blue light while host tissue cells are preserved. Blue light therapy has the potential to rapidly reduce the bacterial load in SSTI.

Blue light rescues mice from potentially fatal Pseudomonas aeruginosa burn infection: efficacy, safety, and mechanism of action.

Blue light has attracted increasing attention due to its intrinsic antimicrobial effect without the addition of exogenous photosensitizers. However, the use of blue light for wound infections has not been established yet. In this study, we demonstrated the efficacy of blue light at 415 nm for the treatment of acute, potentially lethal Pseudomonas aeruginosa burn infections in mice. Our in vitro studies demonstrated that the inactivation rate of P. aeruginosa cells by blue light was approximately 35-fold higher than that of keratinocytes (P = 0.0014). Transmission electron microscopy revealed blue light-mediated intracellular damage to P. aeruginosa cells. Fluorescence spectroscopy suggested that coproporphyrin III and/or uroporphyrin III are possibly the intracellular photosensitive chromophores associated with the blue light inactivation of P. aeruginosa. In vivo studies using an in vivo bioluminescence imaging technique and an area-under-the-bioluminescence-time-curve (AUBC) analysis showed that a single exposure of blue light at 55.8 J/cm(2), applied 30 min after bacterial inoculation to the infected mouse burns, reduced the AUBC by approximately 100-fold in comparison with untreated and infected mouse burns (P < 0.0001). Histological analyses and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling (TUNEL) assays indicated no significant damage in the mouse skin exposed to blue light at the effective antimicrobial dose. Survival analyses revealed that blue light increased the survival rate of the infected mice from 18.2% to 100% (P < 0.0001). In conclusion, blue light therapy might offer an effective and safe alternative to conventional antimicrobial therapy for P. aeruginosa burn infections.

Synergism of epidermal growth factor receptor-targeted immunotherapy with photodynamic treatment of ovarian cancer in vivo.

BACKGROUND: Epithelial ovarian cancer often develops resistance to standard treatments, which is a major reason for the high mortality associated with the disease. We examined the efficacy of a treatment regimen that combines immunotherapy to block the activity of epidermal growth factor receptor (EGFR), overexpression of which is associated with the development of resistant ovarian cancer, and photodynamic therapy (PDT), a mechanistically distinct photochemistry-based modality that is effective against chemo- and radioresistant ovarian tumors. METHODS: We tested a combination regimen consisting of C225, a monoclonal antibody that inhibits the receptor tyrosine kinase activity of EGFR, and benzoporphyrin derivative monoacid A (BPD)-based PDT in a mouse model of human ovarian cancer. Therapeutic efficacy was evaluated in acute treatment response and survival studies that used 9-19 mice per group. Analysis of variance and Wilcoxon statistics were used to analyze the data. All statistical tests were two-sided. RESULTS: Mice treated with PDT + C225 had the lowest mean tumor burden compared with that in the no-treatment control mice (mean percent tumor burden = 9.8%, 95% confidence interval [CI] = 2.3% to 17.3%, P < .001). Mean percent tumor burden for mice treated with C225 only or PDT only was 66.6% (95% CI = 58.7% to 74.4%, P < .001) and 38.2% (95% CI = 29.3% to 47.0%, P < .001), respectively. When compared with PDT only or C225 only, PDT + C225 produced synergistic reductions in mean tumor burden (P < .001, analysis of variance) and improvements in survival (P = .0269, Wilcoxon test). Median survival was approximately threefold greater for mice in the PDT + C225 group than for mice in the no-treatment control group (80 days versus 28 days), and more mice in the PDT + C225 group were alive at 180 days (3/9; 33% [95% CI = 7% to 70%]) than mice in the C225-only (0/12; 0% [95% CI = 0% to 22%]) or PDT-only (1/10; 10% [95% CI = 0.2% to 44%]) groups. CONCLUSION: A mechanistically nonoverlapping combination modality consisting of receptor tyrosine kinase inhibition with C225 and BPD-PDT is well tolerated, effective, and synergistic in mice.