Photosensitization of Staphylococcus aureus with malachite green isothiocyanate: inactivation efficiency and spectroscopic analysis

The potential of malachite green isothiocyanate as a photosensitizer for th e inactivation of bacteria has been evaluated. Samples of Staphylococcus au reus are treated with the dye and exposed to continuous-wave red light from a filtered xenon lamp. Reduction in cell viability is seen to increase wit h radiation dose, whilst non-photosensitized samples are largely unaffected with exposure. The mechanism of photosensitization and the subsequent inac tivation is addressed. UV-Vis and Fourier-transform infrared absorption spe ctrometry have been applied to this biological system, revealing the rapid hydrolysis of the isothiocyanate group of the dye and the transition to the colourless carbinol base when in solution. On binding to Staphylococcus au reus via a complexation mechanism, the dye is seen to be stabilized in its cationic form. Involvement of the excited triplet state of the photosensiti zer is suggested and identification of reduced dye photoproducts is made fo llowing irradiation. (C) 1998 Elsevier Science S.A. All rights reserved.