Photoinactivation Sensitivity of Staphylococcus carnosus to Visible-light Irradiation as a Function of Wavelength.

Abstract

Inactivation properties of visible light are of increasing interest due to multiple possible fields of application concerning antibacterial treatment. For violet wavelengths, the generation of reactive oxygen species by porphyrins is accepted as underlying mechanism. However, there is still little knowledge about photosensitizers at blue wavelengths. While flavins were named as possible candidates, there is still no experimental evidence. This study investigates the photoinactivation sensitivity of Staphylococcus carnosus to selected wavelengths between 390 and 500nm in 10- to 25-nm intervals. Absorption and fluorescence measurements in bacterial lysates confirmed inactivation findings. By means of a mathematical calculation in MATLAB® , a fit of different photosensitizer absorption spectra to the measured action spectrum was determined to gain knowledge about the extent to which specific photosensitizers are involved. The most effective wavelength for S.carnosus at 415nm could be explained by the involvement of zinc protoporphyrin IX. Between 450 and 470nm, inactivation results indicated a broad plateau, statistically distinguishable from 440 and 480nm. This observation points to flavins as responsible photosensitizers, which furthermore seem to be involved at violet wavelengths. A spectral scan of sensitivities might generally be an advantageous approach for examining irradiation impact.