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In order to photosensitize Gram (-) bacteria such as Pseudomonas aeuruginosa and Escherichia coli, we introduced the small peptide polymyxin-B nona-peptide (PBNP) which stimulated the translocation of porphyrin through the outer membrane of these bacteria and makes PDT possible. Gram negative cell killing by the use of PBNP and DP broadens the antibacterial spectrum of photodynamic inactivation and opens new horizons for this modality as a wide spectrum drug when antibiotic resistance is the main concern. Plasmidial and chromosomal DNA damage in S. aureus and E. coli cells was mediated by DP photosensitization. The major observation was the disappearance of the plasmid supercoiled fraction. The chromosomal DNA was also affected and its degradation products were detected after treatment.

bacterial and human leukemic cells were carried out with these sensitizers, in comparison with HPD andPhotofrin II. The new sensitizers were found to have high quantum yields for production of singlet oxygen insolutions. They also have comparable photosensitizing capacities of bacterial cells.1. INTRODUCTIONHematoporphyrin derivative (HPD) and its photoactive fraction Photofrin II (PF-II), have been used forseveral years in photodynamic therapy (PDT) of cancer.14 Their utilization as sensitizers relies on theirselective uptake and retention by cancerous cells,5'6 and on the light-activated cell damage, which is caused byeither an electron or hydrogen transfer from the triplet sensitizer to a substrate, (Type I mechanism), or bysinglet oxygen mediation (Type I1) For clinical applications, long-wavelength light is preferred for its deeperpenetration into the tissue. The light sources which are mainly being used are HeNe and dye lasers or filteredxe lamps. The photosensitization action spectra of Hpd and PF-II exhibit only marginal bands in the red,peaking around 630 nm.78 Therefore, high doses of HPD or PF-II have to be administered, with a resultinglight sensitivity of the whole body for extended periods. The search for new sensitizers with stronger lightabsorption at long wavelengths, which would enable the use of long-wavelength lasers as well as lowering theadministered doses, is currently being pursued.9"°