Mechanism of Bacteriocidal effect by Argon laser

Bactericidal effects by laser irradiation on staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and other bacterial strains have been reported by some researchers, but little attention has been given to the bactericidal mechanism by laser irradiation. In this report, bactericidal mechanism using Argon laser was examined by means of the following method.<BR>a. Bactericidal effects by Argon laser were evaluated by the formation of growth-inhibitory circle of bacteria.<BR>b. The relationship between irradiation output and irradiation time of Argon laser was examined in 5 bacteria including MRSA.<BR>c. The morphological changes in MRSA after laser irradiation were observed by using the transmission electron microscope. As controls, non-irradiated bacteria, heat-treated bacteria and ultraviolet irradiated bacteria were also observed.<BR>d. The bacterial colony were irradiated by laser. The bacteria were stained with acridine orange, and then were compared with non-irradiated bacteria by observing with fluorescence microscope.<BR>e. Change of DNA by laser irradiation on MRSA was studied using Agarose gel electrophoresis.<BR>The results of the experiments were as follows.<BR>a. All bacteria showed a growth inhibitory circle after laser irradiation.<BR>b. By changing irradiation output and irradiation time, we found that there was a close relationship between the total energy per unit area and the appearance of a bactericidal effect, and that Pseudomonas aeruginosa had high sensitivity to the Argon laser compared with other bacteria.<BR>c. The cytoplasm and nucleoid of the bacteria were seen to be higher electron dense lesion. These feature was in good agreement with the image of the cytoplasm of bacteria after heating.<BR>d. After irradiation, fluorescence which acridine orange emitted did not presented difference between irradiated group and non-irradiated group. e. DNA band pattern of MRSA on electrophoresis was not changed after laser irradiation.<BR>In this study, it is suggested that the bactericidal effects on MRSA by Argon laser may be caused mainly by heat rather than photo-dynamic action and that laser may not directly influence band pattern of the DNA in bacteria.