The role of singlet oxygen and oxygen concentration in photodynamic inactivation of bacteria.
New antibacterial strategies are required in view of the increasing resistance of bacteria to antibiotics. One promising technique involves the photodynamic inactivation of bacteria. Upon exposure to light, a photosensitizer in bacteria can generate singlet oxygen, which oxidizes proteins or lipids, leading to bacteria death. To elucidate the oxidative processes that occur during killing of bacteria, Staphylococcus aureus was incubated with a standard photosensitizer, and the generation and decay of singlet oxygen was detected directly by its luminescence at 1,270 nm. At low bacterial concentrations, the time-resolved luminescence of singlet oxygen showed a decay time of 6 +/- 2 micros, which is an intermediate time for singlet oxygen decay in phospholipids of membranes (14 +/- 2 micros) and in the surrounding water (3.5 +/- 0.5 micros). Obviously, at low bacterial concentrations, singlet oxygen had sufficient access to water outside of S. aureus by diffusion. Thus, singlet oxygen seems to be generated in the outer cell wall areas or in adjacent cytoplasmic membranes of S. aureus. In addition, the detection of singlet oxygen luminescence can be used as a sensor of intracellular oxygen concentration. When singlet oxygen luminescence was measured at higher bacterial concentrations, the decay time increased significantly, up to approximately 40 micros, because of oxygen depletion at these concentrations. This observation is an important indicator that oxygen supply is a crucial factor in the efficacy of photodynamic inactivation of bacteria, and will be of particular significance should this approach be used against multiresistant bacteria.
Maisch
Tim
T
Department of Dermatology, University of Regensburg, 93042 Regensburg, Germany.
Baier
Jürgen
J
Franz
Barbara
B
Maier
Max
M
Landthaler
Michael
M
Szeimies
Rolf-Markus
RM
Bäumler
Wolfgang
W
D001426:Bacterial Proteins / Q000378:metabolism; D015169:Colony Count, Microbial; D017323:Dihematoporphyrin Ether / Q000494:pharmacology*; D007700:Kinetics; D007834:Lasers; D049449:Luminescence; D050296:Microbial Viability / Q000187:drug effects* / Q000528:radiation effects; D010100:Oxygen / Q000378:metabolism*; D017319:Photosensitizing Agents / Q000494:pharmacology*; D026082:Singlet Oxygen / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development / Q000528:radiation effects
D001426:Bacterial Proteins; D017319:Photosensitizing Agents; D026082:Singlet Oxygen; D017323:Dihematoporphyrin Ether; D010100:Oxygen