Recently, new antibacteri al strategy has been demanded because of the incr eased occurrence 0 1' drug-resistant bact ena Accordingly , phot odynarnic therapy has been attempted for clinical appli cation against drug-resistant bact eri a, Antimi crobial photodyna rni c t herapy combines a nontoxic photosensiti zer with harmJ ess vi sible light to generate singlet oxygen and free radicals that kill lni croor ganism. In thi s study , we investigated bactericida l effect of photodynarnic ther apy by using phot osensiti zer chl orin e6 to pathogenic bacteria including a gram- positive Stapbylococuus a ureus and gram- negative strains including Pseudomonas aeruginosa, EscbeJicbia coù; and SaJmoneJla en terica sero v，없' 7γpbimurium， To exa때 n e antimicrobial ef fec t 0 1' photodynamic t herapy, we measured inhibition zone‘ colony forrning units (CFU) , and in situ viability of bacteri al cell s after illumination with an energy density (Diode pumped laser driver LD203이 01 20J/cm2 in the presence 0 1' lOuM chlorin e6, We found the incr ease 0 1' inhibition zone on agar plat es‘ the reduction 0 1' colony forming unit , and the rapid decrease 0 1' viable cell number 0 1' all bacterial species exarnined while those 0 1' control bacteria treated so ley wi th ei t her light 0 1' photosensiti zer were unchanged. The susceptibility of 8. aureush and P. aeru - ginosa was much higher t han that 01' the other strains These resu lts show tha t photodynamic t hera py using photosensi ti zer chlorin e6 is very effective to inhibit bacterial s urviva l, suggesti ng t hat t his system can be clin ically appli cable as an alternative antibacterial strategy to treat mul t iple drug-resistant bacteria