Studies of the bactericidal effects of a He-Ne laser combined with toluidine blue O

Abstract

Objective To investigate the effects of photodynamic therapy (PDT) on Staphylococcus aureus and Escherichia coli strains and their laboratory-developed biofilms in vetro and the basic mechanisms of its action.Metods The bacteria were irradiated with a He-Ne laser in the presence of toluidine blue O (TBO).The colony forming units (CFU) of each strain were countde before and after treatment,and the uptakd of TBO by the bacteria was determined using fluorospectrophotometry. Results With a constant light dose,the bactericidal effects of PDT against the two bacteria cultures increasde woth the concentration of TBO,with the strongest bactericidal effect after PDT treatment more than 90%.S.aureus seemed to be more sensitive to PDT than E.coli,though the amount of TBO absorbed by the E.coli cells was significantly larger.The effects of PDT on mature and immature biofilms formed by the two strains showed no significant difference.The bactericidal rate was 20% to 30%.Conclusion Ge-Ne laser irradiation associated with TBO demonstrated significcant photodynamic bactericidal effects on S.arueus and E.coli strains cultivatde in vitro,but the iffects on their biofilms wer limitde.The efficacy of PDT was independent of the absorption of TBO into the bacterial cells. Key words: Photodynamic therapy; Toluidine blue O; He-Ne lasers; Bacteria