Proc. SPIE. 5689, Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIV
KEYWORDS: Defense and security, Photodynamic therapy, Luminescence, Resistance, Scanning electron microscopy, Transmission electron microscopy, Electron microscopy, Photomicroscopy, In vitro testing, Bacteria
We previously demonstrated the methylene blue-mediated photodynamic inactivation of P. aeruginosa in vitro using pulsed light excitation. However, the photobactericidal mechanism has not been revealed yet. In this study, morphological changes induced by pulsed photodynamic treatment in bacteria were investigated by electron microscopy. The micrographs of bacteria showed an alteration in the membrane structure in the early period of illumination, and increase in the total light dose caused an alteration in the cytoplasmic structure. It was shown that the membrane damage may be lethal to bacteria.
Pulsed photodynamic effect on Ps.aeruginosa has been investigated in vitro with the use of methylene blue (MB) as a
photosensitizer. Bacterial suspensions were illuminated with 665-nm, nanosecond light pulses under the various drug
and light dose conditions. Bacterial survival fraction decreased with increasing the drug and light doses, while no
significant bacterial cell death was observed when the bacteria were washed after incubation with the drug. These
results suggest a two-step photo-bactericidal mechanism; the photodynamic effect first induces membrane damage
through which MB molecules were translocated into the bacterial cytoplasm, and then caused bacterial cell death.