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      405 nm and 450 nm photoinactivation of Saccharomyces cerevisiae

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          Abstract

          Photoinactivation of bacteria with visible light has been reported in numerous studies. Radiation around 405 nm is absorbed by endogenous porphyrins and generates reactive oxygen species that destroy bacteria from within. Blue light in the spectral range of 450–470 nm also exhibits an antibacterial effect, but it is weaker than 405 nm radiation, and the photosensitizers involved have not been clarified yet, even though flavins and porphyrins are possible candidates.

          There are significantly fewer photoinactivation studies on fungi. To test if visible light can inactivate fungi and to elucidate the mechanisms involved, the model organism Saccharomyces cerevisiae (DSM no. 70449) was irradiated with violet (405 nm) and blue (450 nm) light. The mean irradiation doses required for a one log reduction of colony forming units for this strain were 182 J/cm 2 and 526 J/cm 2 for 405 nm and 450 nm irradiation, respectively.

          To investigate the cell damaging mechanisms, trypan blue staining was performed. However, even strongly irradiated cultures hardly showed any stained S. cerevisiae cells, indicating an intact cell membrane and thus arguing against the previously suspected mechanism of cell membrane damage during photoinactivation with visible light at least for the investigated strain. The results are compatible with photoinactivated Saccharomyces cerevisiae cells being in a viable but nonculturable state.

          To identify potential fungal photosensitizers, the absorption and fluorescence of Saccharomyces cerevisiae cell lysates were determined. The spectral absorption and fluorescence results are in favor of protoporphyrin IX as the most important photosensitizer at 405 nm radiation. For 450 nm irradiation, riboflavin and other flavins may be the main photosensitizer candidates, since porphyrins do not play a prominent role at this wavelength. No evidence of the involvement of other photosensitizers was found in the spectral data of this strain.

          Most cited references33

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          Trypan blue exclusion test of cell viability.

          W Strober (2001)
          The dye exclusion test is used to determine the number of viable cells present in a cell suspension. It is based on the principle that live cells possess intact cell membranes that exclude certain dyes, such as trypan blue, Eosin, or propidium, whereas dead cells do not. In this test, a cell suspension is simply mixed with dye and then visually examined to determine whether cells take up or exclude dye. In the protocol presented here, a viable cell will have a clear cytoplasm whereas a nonviable cell will have a blue cytoplasm.
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            Comparison of methods used for assessing the viability and vitality of yeast cells.

            Determination of cell viability is the most commonly used method for assessing the impact of various types of stressors in toxicity research and in industrial microbiology studies. Viability is defined as a percentage of live cells in a whole population. Although cell death is one of the consequences of toxicity, chemical or physical factors may exert their toxic effects through a number of cellular alterations that may compromise cell ability to divide without necessarily leading to cell death. This aspect represents the term 'cell vitality' defined as physiological capabilities of cells. It is important to note that cell viability and cell vitality represent two different aspects of cell functions, and both are required for the estimation of the physiological state of a cell after exposure to various types of stressors and chemical or physical factors. In this paper, we introduced a classification of available methods for estimating both viability and vitality in Saccharomyces cerevisiae yeast cells (wild-type and Δsod1 mutant) in which the effects of selected oxidants causing oxidative stress is evaluated. We present the advantages as well as disadvantages of the selected methods and assess their usefulness in different types of research.
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              Antimicrobial blue light inactivation of pathogenic microbes: State of the art.

              As an innovative non-antibiotic approach, antimicrobial blue light in the spectrum of 400-470nm has demonstrated its intrinsic antimicrobial properties resulting from the presence of endogenous photosensitizing chromophores in pathogenic microbes and, subsequently, its promise as a counteracter of antibiotic resistance. Since we published our last review of antimicrobial blue light in 2012, there have been a substantial number of new studies reported in this area. Here we provide an updated overview of the findings from the new studies over the past 5 years, including the efficacy of antimicrobial blue light inactivation of different microbes, its mechanism of action, synergism of antimicrobial blue light with other angents, its effect on host cells and tissues, the potential development of resistance to antimicrobial blue light by microbes, and a novel interstitial delivery approach of antimicrobial blue light. The potential new applications of antimicrobial blue light are also discussed.

                Author and article information

                Journal
                1886
                European Journal of Microbiology and Immunology
                EuJMI
                Akadémiai Kiadó
                2062-8633
                December 2018
                : 8
                : 4
                : 142-148
                Affiliations
                [ 1 ] Ulm University of Applied Sciences , Albert-Einstein-Allee 55, D 89081 Ulm, Germany
                [ 2 ]Institute of Medical Microbiology and Hygiene, University of Ulm , Ulm, Germany
                Author notes
                [*]

                Author for correspondence: Ulm University of Applied Sciences – Institute of Medical Engineering and Mechatronics (Biotechnology Lab), Albert-Einstein- Allee 55, D-89081 Germany; Phone +49 (0) 731 5028603; Fax: +49 (0) 731 5028603; E-mail: hessling@ 123456hs-ulm.de .

                Article
                10.1556/1886.2018.00023
                6348701
                30719331
                6d4fdb3f-64c5-46c1-b839-beae2046f713
                © 2018 The Author(s)

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (https://creativecommons.org/licenses/by-nc/4.0/), which permits unrestricted use, distribution, and reproduction in any medium for non-commercial purposes, provided the original author and source are credited, a link to the CC License is provided, and changes - if any - are indicated.

                History
                : 31 August 2018
                : 21 September 2018
                : 6 December 2018
                Page count
                Pages: 7
                Categories
                Original Research Paper

                Medicine,Immunology,Health & Social care,Microbiology & Virology,Infectious disease & Microbiology
                flavin,450 nm irradiation,405 nm irradiation,disinfection,photoinactivation, Saccharomyces cerevisiae ,porphyrin

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