The aim of the present study is to evaluate the antimicrobial effect of photodynamic therapy (PDT) using a highly pure chlorin e(6) (Ce(6)), against various pathogenic bacteria. To examine the antimicrobial effect of Ce(6)-mediated PDT against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, and Salmonella enterica serovar Typhimurium, inhibition zone formation, CFU quantification, and bacterial viability were evaluated. Inhibition zone analysis showed that Ce(6)-mediated PDT is very effective to inhibit the growth of S. aureus and P. aeruginosa, but has only minor effect to E. coli and S. Typhimurium, which was dependent on the energy density of laser and dose of Ce(6). Ce(6)-mediated PDT also nearly inhibited the colony formation of S. aureus and P. aeruginosa, and partially inhibited that of E. coli and S. Typhimurium. In addition, the number of viable bacteria decreased greatly after PDT application with LS-chlorin e6 of 10 microM and laser and energy density of 20 J/cm(2). These results show that Ce(6)-mediated PDT can be an effective alternative for antimicrobial treatment.