In vitro Photodynamic Antimicrobial Activity of Protoporphyrin IX in the Presence of Hydrogen Peroxide against Staphylococcus aureus and Pseudomonas aeruginosa.

Aims: This study reports on In vitro investigation of photodynamic antimicrobial activity of protoporphyrin IX (PPIX) in the presence and absence of Hydrogen peroxide (H2O2) against S. aureus and P. aeruginosa. Place and Duration of Study: Department of Medical Physics, Anna University, Chennai between December 2013 and February 2014. Methodology: A light-emitting diode (LED) was used as a light source to irradiate PPIX. The antibacterial effect was analyzed by standard plate counting method. Steady-state fluorescence spectroscopy technique was used to monitor the damage at protein level. Results: We found that the antibacterial effect is dependent on PPIX concentration as well as H2O2 concentration and light dose. PPIX-H2O2 combination showed higher bacterial reduction of 6.5 log10 and 2.7 log10 for S. aureus and P. aeruginosa respectively, when the light dose increased to 70 J/cm2. Fluorescence spectroscopic characterization showed a considerable change in the intensity of emission of tryptophan present in the microorganisms between pre- and post- APDT. Conclusion: PPIX-H2O2 is a promising combination for APDT against Gram positive and Gram negative bacteria. The LED seems to be a very good option for PDT because of its low cost and miniature in size.