الفهرس 
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Abstract
The effect of very low dose gamma irradiation, up to 2.0 Gy, increased the sensitivity of resistant S. aureus to gentamycin, ciprofloxacin, and amoxicillin. The increase in sensitivity of the irradiated S. aureus may result in formation of micro cracks in the cell wall rendering the penetration of antibiotics through it and causing the bactericidal effect. Although the decrease in the differential adherent (not released) polysaccharides for both S. aureus and P. aeruginosa after low dose gamma irradiation, the later showed no increase in antibiotic sensitivity to the same types of antibiotics. It was found that photodynamic inactivation (PDI) is a promising approach to the killing of both Gram-positive and Gram-negative bacteria of the skin. The results revealed that PDI in the presence of hematoporphyrin dihydrochloride dye as a photosensitizer and light (L+P+) was able to reduce the viability of both S. aureus and P. aeruginosa species. The response of S. aureus to photosnsitizer in absence of light (L-P+) or to light in absence of photosensitizer (L+P-) was very weak while P. aeruginosa had no response in absence of photosensitizer.