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

Abstract

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.