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Lethal photosensitization of wound-associated microbes using indocyanine green and near-infrared light
Ghada S Omar1, Michael Wilson, Sean P Nair
1Division of Microbial Diseases, UCL Eastman Dental Institute, University College London, 256 Gray's Inn Road, London WC1X 8LD, UK. g.omar@eastman.ucl.ac.uk
Background:
The increase in resistance to antibiotics among disease-causing bacteria necessitates the development of alternative antimicrobial approaches such as the use of light-activated antimicrobial agents (LAAAs). Light of an appropriate wavelength activates the LAAA to produce cytotoxic species which can then cause bacterial cell death via loss of membrane integrity, lipid peroxidation, the inactivation of essential enzymes, and/or exertion of mutagenic effects due to DNA modification. In this study, the effect of the LAAA indocyanine green excited with high or low intensity light (808 nm) from a near-infrared laser (NIR) on the viability of Staphylococcus aureus, Streptococcus pyogenes and Pseudomonas aeruginosa was investigated.
Results:
All species were susceptible to killing by the LAAA, the bactericidal effect being dependent on both the concentration of indocyanine green and the light dose. Indocyanine green photosensitization using both high (1.37 W cm(-2)) and low (0.048 W cm(-2)) intensity NIR laser light was able to achieve reductions of 5.6 log10 (>99.99%) and 6.8 log10 (>99.99%) in the viable counts of Staph. aureus and Strep. pyogenes (using starting concentrations of 106-107 CFU ml(-1)). Kills of 99.99% were obtained for P. aeruginosa (initial concentration 108-109 CFU ml(-1)) photosensitized by the high intensity light (1.37 W cm(-2)); while a kill of 80% was achieved using low intensity irradiation (0.07 W cm(-2)). The effects of L-tryptophan (a singlet oxygen scavenger) and deuterium oxide (as an enhancer of the life span of singlet oxygen) on the survival of Staph. aureus was also studied. L-tryptophan reduced the proportion of Staph. aureus killed; whereas deuterium oxide increased the proportion killed suggesting that singlet oxygen was involved in the killing of the bacteria.
Conclusion:
These findings imply that indocyanine green in combination with light from a near-infrared laser may be an effective means of eradicating bacteria from wounds and burns.
Insights
Indocyanine green activated by near-infrared laser light effectively kills bacteria like Staphylococcus aureus and Pseudomonas aeruginosa. This light-activated antimicrobial approach shows promise for treating wound and burn infections.
Area of Science:
- Antimicrobial photodynamic therapy
- Bacteriology
- Biomedical engineering
Background:
- Antibiotic resistance necessitates novel antimicrobial strategies.
- Light-activated antimicrobial agents (LAAAs) offer a promising alternative.
- Indocyanine green (ICG) is a potential LAAA for bacterial inactivation.
Purpose of the Study:
- To investigate the efficacy of ICG combined with near-infrared (NIR) laser light against key bacterial pathogens.
- To evaluate the impact of light intensity and ICG concentration on bacterial viability.
- To elucidate the mechanism of bacterial killing by ICG-mediated photosensitization.
Main Methods:
- Exposure of Staphylococcus aureus, Streptococcus pyogenes, and Pseudomonas aeruginosa to ICG.
- Irradiation using an 808 nm NIR laser at high (1.37 W cm⁻²) and low (0.048 W cm⁻²) intensities.
- Assessment of bacterial viability through colony counting.
- Inclusion of singlet oxygen scavengers (L-tryptophan) and enhancers (deuterium oxide) to study the mechanism.
Main Results:
- ICG and NIR light demonstrated significant bactericidal effects against all tested species.
- Bacterial killing was dependent on both ICG concentration and light dose.
- High-intensity NIR light achieved >99.99% kill for S. aureus and S. pyogenes, and 99.99% for P. aeruginosa.
- Low-intensity NIR light showed reduced efficacy against P. aeruginosa (80% kill).
- Deuterium oxide enhanced killing, while L-tryptophan reduced it, indicating singlet oxygen involvement.
Conclusions:
- Indocyanine green combined with NIR laser light is a potent antimicrobial agent.
- This approach shows potential for eradicating bacteria in wound and burn infections.
- The findings support the development of ICG-based photodynamic therapy for challenging infections.
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