CC BY
8B-O-17
BIOMEDICAL PHOTONICS
Bactericidal and Bacteriostatic Effect of Blue Light: Basic Patterns and Methods for the Efficiency Enhancement
V. Plavskii1, A. Tretyakova1, A. Mikulich1, N. Dudchik2, O. Emelyanova2, L. Plavskaya1, T. Ananich1, O. Dudinova1, A. Sobchuk1, R. Nahorny1, I. Leusenko1, S. Yakimchuk1
1- Institute of Physics of the NAS of Belarus, 68-2 Nezavisimosti Ave., Minsk, 220072, Republic of Belarus 2- Republican Unitary Enterprise «Scientific Practical Centre of Hygiene», 8 Akademicheskaya str.,
Minsk, 220012, Republic of Belarus v.plavskii@ifanbel.bas-net.by
It was believed for a long time, that only radiation of the short-wave ultraviolet range (200-300 nm), corresponding to the absorption spectrum of DNA, has an antimicrobial effect. However, the studies performed during the last decade with the use of the appeared intense light sources (super-bright LEDs, semiconductor lasers) convincingly indicate the ability of blue light to have a bactericidal or bacteriostatic effect without introducing external exogenous dye-photosen-sitizers to irradiated microorganisms.
Our studies made it possible to find out the main patterns of the antimicrobial effect of blue light and to develop methods for enhancing its bactericidal and bacteriostatic effectiveness:
It has been established that the exposure of laser radiation of violet and blue spectrum regions to suspensions of microbial cells leads to suppression of growth of both gram-positive streptococci S. aureus and gram-negative E. coli, as well as yeast-like fungi C. albicans, having significantly different structure of the cell membrane. No significant difference in photosensitivity of gram-negative and gram-positive bacteria to the action of radiation of the same wavelength has been revealed. At the same time, among various cell phenotypes, the types with high resistance to the blue light have been found.
It has been established that endogenous metal-free porphyrins, as well as zinc complexes of porphyrins and flavin compounds having photosensitizing properties, act as acceptors of optical radiation, which determine the antimicrobial effect of this physical factor. The participation of these compounds in realization of the antimicrobial effect of laser radiation is indicated by the registration of porphyrin and flavin fluorescence in extracts of microbial cells upon excitation by radiation used to inactivate pathogens. The contribution of porphyrin photosensitizers is mostly pronounced at the exposure with 405 nm radiation (maximum of the Soret band of porphyrins), and flavin ones - at the exposure with 445 nm radiation (maximum in the absorption spectrum of flavins and minimum in the absorption spectrum of porphyrins). The ratio between the intensity of the porphyrin and flavin components in the fluorescence spectrum of extracts depends on the type of microbial cells.
A characteristic feature of the effect of the blue light on microbial cells is an increase of the speed of their photoin-activation with an increase in the dose of radiation. In our opinion, this type of dose dependence can be explained by the model of many photoinactivation targets, assuming that each cell contains not one, but several sensitive targets important for cell life, and a certain number of these targets must be hit to inactivate the cell. Indeed, under the blue spectrum region radiation exposure on microbial cells, there is a violation of the integrity and loss of the most important functional characteristics of cell membranes, release of DNA into the extracellular environment, as well as the oxidation of intracellular DNA, depletion of the level of intracellular ATP due to inhibition of ATPhase, photodamage of some enzymes, as well as a range of metabolites. All this supports the model of many targets of cellular photoinactivation. This conclusion is also supported by the formation of complexes of endogenous porphyrins with molecules of some enzymes, as well as DNA, that we have established.
It has been shown that the effectiveness of the method of suppressing the growth of microorganisms by exposure with laser radiation of the blue spectrum region can be significantly enhanced by: a) the use of radiation of two wavelengths addressed to different cellular targets; b) the use of pulsed radiation, characterized by a high amplitude value of the intensity; c) selection of the optimal wavelength corresponding to the effective excitation of various cellular photosensitizers.
ALT'22
