Photodynamic inactivation of antibiotic resistant strain of Pseudomonas aeruginosa by porphyrins induced by delta-aminolaevulinic acid.

BACKGROUND & OBJECTIVES: The widespread occurrence of antibiotic resistant strains of Pseudomonas aeruginosa in hospitals is a matter of growing concern. We report the results of a study on photodynamic inactivation of antibiotic resistant strain of P. aeruginosa by delta-aminolaevulinic acid (ALA). METHODS: Exponentially growing P. aeruginosa cells were incubated in growth medium with ALA for various durations. Subsequently, the cells were washed and resuspended in phosphate buffered saline (PBS). These cells were incubated with different concentrations of glutathione (GSH) in PBS for 15 min. Porphyrins synthesized with and without GSH were detected by fluorescence spectroscopy. The ALA treated cells were irradiated with light at 405 nm with and without subsequent incubation in GSH. Cell survival was measured by colony forming ability. RESULTS: Incubation of cells in growth medium with ALA led to increased synthesis of protoporphyrins in cells which saturated beyond 4 h. The level of protoporphyrin synthesis increased significantly when ALA treated cells were subsequently incubated with GSH in PBS for 15 min. Irradiation of cells incubated with ALA alone led to weak inactivation. However, substantial cell death was observed in ALA treated cells irradiated in the presence of 15 mM GSH. INTERPRETATION & CONCLUSION: Photodynamic inactivation of P. aeruginosa by ALA induced porphyrins can be enhanced if ALA treated cells are further incubated with GSH and irradiated using 405 nm light. These findings may be useful for inactivation of antibiotic resistant strains of P. aeruginosa causing burn and wound infections in hospitalized patients.

Photodynamic action of merocyanine 540 on carcinoma of cervix cells.

Results of the studies carried out on localization and photodynamic action of merocyanine 540 (MC540) on carcinoma of cervix (HeLa) cells are presented. Fluorescence microscopic study showed that when HeLa cells were incubated with MC540 in dark, the dye localized in plasma membrane of cells. Photoirradiation of cells in presence of MC540 led to enhancement of dye uptake, intracellular localization of dye and a dose dependent decrease in cell survival. Clonogenic assay showed 96% cell killing at a light dose of 42 kJ/m2. Photosensitization of cells resulted in loss of membrane integrity, decrease in plasma membrane fluidity and reduction in mitochondrial dehydrogenase activity as measured by tetrazolium reduction (MTT) assay. At a given light dose, the relative change in plasma membrane properties was higher than the reduction in activity of mitochondrial enzyme. These results suggest plasma membrane is a primary target of photosensitization of HeLa cells by MC540.