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      405 nm and 450 nm photoinactivation of Saccharomyces cerevisiae

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          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.

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          Most cited references 31

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          Eradication of Propionibacterium acnes by its endogenic porphyrins after illumination with high intensity blue light.

          Propionibacterium acnes is a Gram-positive, microaerophilic bacterium that causes skin wounds. It is known to naturally produce high amounts of intracellular porphyrins. The results of the present study confirm that the investigated strain of P. acnes is capable of producing endogenic porphyrins with no need for any trigger molecules. Extracts from growing cultures have demonstrated emission peaks around 612 nm when excited at 405 nm, which are characteristic for porphyrins. Endogenic porphyrins were determined and quantified after their extraction from the bacterial cells by fluorescence intensity and by elution retention time on high-performance liquid chromatography (HPLC). The porphyrins produced by P. acnes are mostly coproporphyrin, as shown by the HPLC elution patterns. Addition of delta-aminolevulinic acid (ALA) enhanced intracellular porphyrin synthesis and higher amounts of coproporphyrin have been found. Eradication of P. acnes by its endogenic porphyrins was examined after illumination with intense blue light at 407-420 nm. The viability of 24 h cultures grown anaerobically in liquid medium was reduced by less than two orders of magnitude when illuminated once with a light dose of 75 J cm(-2). Better photodynamic effects were obtained when cultures were illuminated twice or three times consecutively with a light dose of 75 J cm(-2) and an interval of 24 h between illuminations. The viability of the culture under these conditions decreased by four orders of magnitude after two illuminations and by five orders of magnitude after three illuminations. When ALA-triggered cultures were illuminated with intense blue light at a light dose of 75 J cm(-2) the viability of the treated cultures decreased by seven orders of magnitude. This decrease in viability can occur even after a single exposure of illumination for the indicated light intensity. X-ray microanalysis and transmission electron microscopy revealed structural damages to membranes in the illuminated P. acnes. Illumination of the endogenous coproporphyrin with blue light (407-420 nm) apparently plays a major role in P. acnes photoinactivation. A treatment protocol with a series of several illuminations or illumination after application of ALA may be suitable for curing acne. Treatment by both pathways may overcome the resistance of P. acnes to antibiotic treatment.
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            In vitro bactericidal effects of 405-nm and 470-nm blue light.

            The aim of this study was to determine the bactericidal effect of 405- and 470-nm light on two bacteria, Staphylococcus aureus and Pseudomonas aeruginosa, in vitro. It is well-known that UV light kills bacteria, but the bactericidal effects of UV may not be unique since recent studies indicate that blue light produces a somewhat similar effect. The effects of blue light seem varied depending on wavelength, dose and the nature of the bacteria, hence this study. Two common aerobes, Staphylococcus aureus and Pseudomonas aeruginosa, and anaerobic Propionibacterium acnes were tested. Each organism was treated with Super Luminous Diode probes with peak emission at 405 and 470 nm. Treatment was timed to yield 1, 3, 5, 10, and 15 Jcm2 doses. Colony counts were performed and compared to untreated controls. The 405-nm light produced a dose dependent bactericidal effect on Pseudomonas aeruginosa and Staphylococcus aureus (p < .05), achieving as much as 95.1% and nearly 90% kill rate for each, respectively. The 470-nm light effectively killed Pseudomonas aeruginosa at all dose levels, but only killed Staphylococcus aureus at 10 and 15 J cm2. With this wavelength, as much as 96.5% and 62% reduction of Pseudomonas aeruginosa and Staphylococcus aureus was achieved, respectively. Neither of the two wavelengths proved bactericidal with anaerobic Propionibacterium acnes. The results indicate that, in vitro, 405- and 470-nm blue light produce dose dependent bactericidal effects on Pseudomonas aeruginosa and Staphylococcus aureus but not Propionibacterium acnes.
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              Helicobacter pylori accumulates photoactive porphyrins and is killed by visible light.

              Helicobacter pylori colonizes the mucus layer of the human stomach and duodenum, causes chronic gastritis, gastric ulcer, and is a risk factor for gastric adenocarcinoma. There is a 20% failure rate in antibiotic therapy, which is increasingly due to antibiotic resistance and necessitates the search for alternative antimicrobial methods. We have discovered that H. pylori when cultured in liquid medium, accumulates significant quantities of coproporphyrin and protoporphyrin IX, both in the cells and secreted into the medium. These photoactive porphyrins lead to cell death (up to 5 logs) by photodynamic action upon illumination with low doses of visible light, with blue/violet light being most efficient. The degree of killing increases with the age of the culture and is greater than that found with Propionibacterium acnes (another bacterium known to be photosensitive due to porphyrin accumulation). Both virulent and drug-resistant strains are killed. The data suggest that phototherapy might be used to treat H. pylori infection in the human stomach.

                Author and article information

                European Journal of Microbiology and Immunology
                Akadémiai Kiadó
                December 2018
                : 8
                : 4
                : 142-148
                [ 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@ .

                © 2018 The Author(s)

                This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License (, 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.

                Page count
                Pages: 7
                Original Research Paper


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