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Killing of cutaneous microbial species by photodynamic therapy
B Zeina1, J Greenman, W M Purcell
1Dermatology Department of Teshreen Hospital, Damascus, Syria.
Background:
Photodynamic therapy (PDT) utilizes photosensitizers and light. Whereas PDT use in cancer treatment has been widely accepted, antimicrobial PDT (APDT) is still in its early stages of development.
Objectives:
To study microbial killing in vitro using APDT.
Methods:
We used a combination of methylene blue and visible light, and a range of microbial species representative of those encountered on the skin in health and disease. Using standard light intensity conditions (slide projector, 25 cm distance from target, 42 mW cm(-2)) and methylene blue dye at 100 microg mL(-1), kill rates and subsequent D-values were determined against Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes, Corynebacterium minutissimum, Propionibacterium acnes and Candida albicans.
Results:
D-values for these species were 72, 66, 48, 120, 30 and 660 s, respectively. The effects of light intensity on the killing of S. epidermidis showed the kill rate to be proportional to the light intensity. A high rate of cell kill was also obtained using natural sunlight.
Conclusions:
Overall, these results indicate that APDT of the skin may represent a useful alternative to conventional antimicrobial treatment.
Insights
Antimicrobial photodynamic therapy (APDT) effectively kills various skin microbes in vitro using methylene blue and light. This research shows APDT is a promising alternative to traditional antimicrobial treatments.
Area of Science:
- Photochemistry
- Microbiology
- Dermatology
Background:
- Photodynamic therapy (PDT) is established for cancer treatment.
- Antimicrobial PDT (APDT) is an emerging therapeutic strategy.
- APDT utilizes photosensitizers and light to eliminate microbes.
Purpose of the Study:
- To evaluate the efficacy of APDT against common skin microorganisms in vitro.
- To determine microbial kill rates and D-values using methylene blue and visible light.
Main Methods:
- Methylene blue (100 µg mL⁻¹) and visible light were used for APDT.
- Standardized light intensity (42 mW cm⁻²) was applied.
- Kill rates and D-values were assessed against Staphylococcus aureus, S. epidermidis, Streptococcus pyogenes, Corynebacterium minutissimum, Propionibacterium acnes, and Candida albicans.
Main Results:
- D-values varied significantly across species, ranging from 30 s (P. acnes) to 660 s (C. albicans).
- Microbial kill rate for S. epidermidis was proportional to light intensity.
- Effective microbial killing was also achieved using natural sunlight.
Conclusions:
- APDT demonstrates potent antimicrobial activity against a spectrum of skin microbes.
- The findings suggest APDT is a viable alternative to conventional antimicrobial therapies for skin infections.