Physical and mathematical modeling of antimicrobial photodynamic therapy

[The effectiveness of photodynamic effects on the clinical and functional state of periodontal tissues in periodontitis]

The aim the study. Increasing the effectiveness of treatment of chronic generalized periodontitis of moderate severity according to microhemodynamics and oxygenation in periodontal tissues.

MATERIALS AND METHODS

A clinical and functional study and treatment of chronic generalized periodontitis of moderate degree were conducted in 56 people (22 men and 34 women) aged 37 to 55 years. The patients were divided into 2 groups depending on the type of treatment: group 1 (main) - 28 people (11 men and 17 women, the average age of the group was 43.5±2.8 years, photodynamic therapy (PDT) with 1% dimegin gel using an AFS Spectrum LED emitter with a wavelength of 660 nm and an energy density of 95 J/cm2), in group 2 (control) - 28 people. (9 men and 19 women, the average age of the group was 45.0±3.1 years) standard treatment was performed without PDT. The level of tissue blood flow, its activity and vasomotor activity of microvessels, as well as the blood flow bypass index were determined by laser Doppler flowmetry. The study of oxygenation was carried out by optical tissue oximetry with determination of the index of oxygenation, specific oxygen consumption and perfusion oxygen saturation.

RESULTS

After PDT, the periodontal tissues showed an increase in blood flow by 65.5% after 3 months, the level of oxygen metabolism increased by 51%, which increased after 6 months. The use of PDT in the complex treatment of chronic generalized periodontitis of moderate severity has an activating effect on the microcirculation system and the level of oxygen metabolism in periodontal tissues both in the near and long-term follow-up periods.

CONCLUSIONS

The use of PDT with 1% dimegin gel has an effective effect on the state of microhemodynamics and oxygenation in periodontal tissues.

Lifetime and diffusion distance of singlet oxygen in air under everyday atmospheric conditions

Singlet oxygen is a toxic chemical but powerful oxidant, exploited in many chemical and biological applications. However, the lifetime of singlet oxygen in air under atmospheric conditions is yet to be known. This has limited safe usage of singlet oxygen in air, despite being a strong antimicrobial agent with the unique property of relaxing to breathable oxygen after serving its purpose. Here, we solve this long-standing problem by combining experimental and theoretical research efforts; we generate singlet oxygen using a photosensitizer at a local source and monitor the time-dependent extent of singlet oxygen reaction with probe molecules at a detector, precisely controlling the detector distance from the source. To explain our experimental results, we employ a theoretical model that fully accounts for singlet oxygen diffusion, radiative and nonradiative relaxations, and the bimolecular reaction with probe molecules at the detector. For all cases investigated, our model, with only two adjustable parameters, provides an excellent quantitative explanation of the experiment. From this analysis, we extract the lifetime of singlet oxygen in the air to be 2.80 s at 23 °C under 1 atm, during which time singlet oxygen diffuses about 0.992 cm. The correctness of this estimation is confirmed by a simple mean-first-passage time analysis of the maximum distance singlet oxygen can reach from the source. We also confirm the sterilization effects of singlet oxygen for distances up to 0.6-0.8 cm, depending on the bacteria strain in question, between the bacteria and the singlet oxygen source.

Inactivation of Vibrio parahaemolyticus by antimicrobial photodynamic technology using methylene blue

BACKGROUND

Vibrio parahaemolyticus is the leading causative pathogen of gastroenteritis often related to contaminated seafood. Photodynamic inactivation has been recently proposed as a strategy for killing cells and viruses. The objective of this study was to verify the bactericidal effects caused by photodynamic inactivation using methylene blue (MB) over V. parahaemolyticus via flow cytometry, agarose gel electrophoresis and sodium dodecyl sulfate polyacrylamide gel electrophoresis. Vibrio parahaemolyticus counts were determined using the most probable number method. A scanning electron microscope and a transmission electron microscope were employed to intuitively analyze internal and external cell structure.

RESULTS

Combination of MB and laser treatment significantly inhibited the growth of V. parahaemolyticus. The inactivation rate of V. parahaemolyticus was >99.99% and its counts were reduced by 5 log10 in the presence of 0.05 mg mL(-1) MB when illuminated with visible light (power density 200 mW cm(-2)) for 25 min. All inactivated cells showed morphological changes, leakage of cytoplasm and degradation of protein and DNA.

CONCLUSION

Results from this study indicated that photodynamic technology using MB produced significant inactivation of V. parahaemolyticus mainly brought about by the degradation of protein and DNA.