Tim Maisch, Jürgen Baier, Barbara Franz, Max Maier, Michael Landthaler, Rolf-Markus Szeimies, and Wolfgang Bäumler
(T. Maisch, J. Baier, B. Franz, M. Maier, M. Landthaler, R.-M. Szeimies, and W. Bäumler)

Proceedings of the National Academy of Sciences of the United States of America, April 2007, Volume 104, Issue 17, Page 7223-7228
(Proc. Natl. Acad. Sci. U.S.A. (PNAS) 104 (17): 7223. (2007))

doi:10.1073/pnas.0611328104

Abstract:
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 µs, which is an intermediate time for singlet oxygen decay in phospholipids of membranes (14 ± 2 µs) and in the surrounding water (3.5 ± 0.5 µs). 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 approx 40 µs, 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.

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