The Efficiency of Photodynamic Inactivation (PDI) on Increasing the Sensitivity of antibiotic Resistant S. aureus and P. aeruginosa Isolated from Human Infected Skin

Two antibiotic resistant bacterial isolates, Staphylococcus. Aureus and Pseudomonas. aeruginosa were exposed to hematoporphyrin dihydrochloride (Hp) as a photo sensitizer and photodynamic visible light to eliminate them from infected skin. Dark toxicity for S. aureus increased with increasing Hp concentration and reached the maximum reduction percentage in viable count (20%) at 250 {mu}g/ml. However, P. aeruginosa showed no dark toxicity for the same Hp concentrations. Twenty five {mu}g/ml of Hp and light dose of 27 J/cm{sup 2} for 30 min. were able to reduce 50.4% of S. aureus viability while it had no effect on P. aeruginosa. S. aureus was relatively sensitive to photo sensitizer in the absence of light while P. aeruginosa was not . Twenty five hundred {mu} g/ml of Hp combined with light dose of 27 J/cm{sup 2} for 30 min. reduced the viable count of S.aureus and P. aeruginosa to 100% and 66.7%, respectively .In absence of photo sensitizer laser light reduced 10.1% of S.aureus and 26.2% of, P. aeruginosa respectively. Low fluency rate (4.5 J/cm{sup 2}) combined with 100 {mu} g/ml of Hp photodynamic reduced 20% of S .aureus cells .The reducing percentage gradually increased to 35% ,50 % and 93% at fluency rate 9 J/cm{sup 2},18 J/cm{sup 2} and 27 J/cm{sup 2}. Low fluency rate (4.5 J/cm{sup 2}) combined with 250 {mu} g/ml of Hp reduced the viability of P .aeruginosa cells by 6.7% .By increasing the fluency rate to 9, 18, and 27 J/cm{sup 2}, the reducing percentage was gradually increased to 30%, 43.3% to 66.7%, respectively. Treatment of P. aeruginosa cells with EDTA (10 mM) for one hour before application of (PDI) showed a great increase in reduction percentage of viable count (99.9%) compared to 66.7 % achieved by PHI in absences of EDTA. The effect of acetic acid at the concentrations between 0.5 and 4 % to eliminate Pseudomonas aeruginosa was tested. The optimum concentration of acetic acid to kill about 99.5% of P. aeruginosa without harming the surrounding tissues was about 3.0%.