Publications by authors named "Katharina Hoenes"

11 Publications

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Microbial Photoinactivation by Visible Light Results in Limited Loss of Membrane Integrity.

Antibiotics (Basel) 2021 Mar 23;10(3). Epub 2021 Mar 23.

Institute of Medical Engineering and Mechatronics, Ulm University of Applied Sciences, 89081 Ulm, Germany.

Interest in visible light irradiation as a microbial inactivation method has widely increased due to multiple possible applications. Resistance development is considered unlikely, because of the multi-target mechanism, based on the induction of reactive oxygen species by wavelength specific photosensitizers. However, the affected targets are still not completely identified. We investigated membrane integrity with the fluorescence staining kit LIVE/DEAD BacLight™ on a Gram positive and a Gram negative bacterial species, irradiating and with 405 nm and 450 nm. To exclude the generation of viable but nonculturable (VBNC) bacterial cells, we applied an ATP test, measuring the loss of vitality. Pronounced uptake of propidium iodide was only observed in at 405 nm. Transmission electron micrographs revealed no obvious differences between irradiated samples and controls, especially no indication of an increased bacterial cell lysis could be observed. Based on our results and previous literature, we suggest that visible light photoinactivation does not lead to rapid bacterial cell lysis or disruption. However, functional loss of membrane integrity due to depolarization or inactivation of membrane proteins may occur. Decomposition of the bacterial envelope following cell death might be responsible for observations of intracellular component leakage.
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http://dx.doi.org/10.3390/antibiotics10030341DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8005082PMC
March 2021

Photoinactivation of Staphylococci with 405 nm Light in a Trachea Model with Saliva Substitute at 37 °C.

Healthcare (Basel) 2021 Mar 11;9(3). Epub 2021 Mar 11.

Institute of Medical Engineering and Mechatronics, Ulm University of Applied Sciences, 89081 Ulm, Germany.

The globally observed rise in bacterial resistance against antibiotics has increased the need for alternatives to antibiotic treatments. The most prominent and important pathogen bacteria are the ESKAPE pathogens, which include among others , and . These species cause ventilator-associated pneumonia (VAP), which accounts for 24% of all nosocomial infections. In this study we tested the efficacy of photoinactivation with 405 nm violet light under conditions comparable to an intubated patient with artificial saliva for bacterial suspension at 37 °C. A technical trachea model was developed to investigate the visible light photoinactivation of as a non-pathogen surrogate of the ESKAPE pathogen (MRSA). The violet light was coupled into the tube with a fiber optic setup. The performed tests proved, that photoinactivation at 37 °C is more effective with a reduction of almost 3 log levels (99.8%) compared to 25 °C with a reduction of 1.2 log levels. The substitution of phosphate buffered saline (PBS) by artificial saliva solution slightly increased the efficiency during the experimental course. The increased efficiency might be caused by a less favorable environment for bacteria due to for example the ionic composition.
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http://dx.doi.org/10.3390/healthcare9030310DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7998829PMC
March 2021

Inactivation Effect of Violet and Blue Light on ESKAPE Pathogens and Closely Related Non-pathogenic Bacterial Species - A Promising Tool Against Antibiotic-Sensitive and Antibiotic-Resistant Microorganisms.

Front Microbiol 2020 13;11:612367. Epub 2021 Jan 13.

Institute of Medical Engineering and Mechatronics, Ulm University of Applied Sciences, Ulm, Germany.

Due to the globally observed increase in antibiotic resistance of bacterial pathogens and the simultaneous decline in new antibiotic developments, the need for alternative inactivation approaches is growing. This is especially true for the treatment of infections with the problematic ESKAPE pathogens, which include , and species, and often exhibit multiple antibiotic resistances. Irradiation with visible light from the violet and blue spectral range is an inactivation approach that does not require any additional supplements. Multiple bacterial and fungal species were demonstrated to be sensitive to this disinfection technique. In the present study, pathogenic ESKAPE organisms and non-pathogenic relatives are irradiated with visible blue and violet light with wavelengths of 450 and 405 nm, respectively. The irradiation experiments are performed at 37°C to test a potential application for medical treatment. For all investigated microorganisms and both wavelengths, a decrease in colony forming units is observed with increasing irradiation dose, although there are differences between the examined bacterial species. A pronounced difference can be observed between Acinetobacter, which prove to be particularly light sensitive, and enterococci, which need higher irradiation doses for inactivation. Differences between pathogenic and non-pathogenic bacteria of one genus are comparatively small, with the tendency of non-pathogenic representatives being less susceptible. Visible light irradiation is therefore a promising approach to inactivate ESKAPE pathogens with future fields of application in prevention and therapy.
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http://dx.doi.org/10.3389/fmicb.2020.612367DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7838345PMC
January 2021

Photoinactivation of the Coronavirus Surrogate phi6 by Visible Light.

Photochem Photobiol 2021 01 21;97(1):122-125. Epub 2020 Nov 21.

Ulm University of Applied Sciences, Ulm, Germany.

To stop the coronavirus spread, new inactivation approaches are being sought that can also be applied in the presence of humans or even on humans. Here, we investigate the effect of visible violet light with a wavelength of 405 nm on the coronavirus surrogate phi6 in two aqueous solutions that are free of photosensitizers. A dose of 1300 J cm of 405 nm irradiation reduces the phi6 plaque-forming unit concentration by three log-levels. The next step should be similar visible light photoinactivation investigations on coronaviruses, which cannot be performed in our lab.
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http://dx.doi.org/10.1111/php.13352DOI Listing
January 2021

Enhancement of Contact Lens Disinfection by Combining Disinfectant with Visible Light Irradiation.

Int J Environ Res Public Health 2020 09 3;17(17). Epub 2020 Sep 3.

Institute of Medical Engineering and Mechatronics, Ulm University of Applied Sciences, Albert-Einstein-Allee 55, 89081 Ulm, Germany.

Multiple use contact lenses have to be disinfected overnight to reduce the risk of infections. However, several studies demonstrated that not only microorganisms are affected by the disinfectants, but also ocular epithelial cells, which come into contact via residuals at reinsertion of the lens. Visible light has been demonstrated to achieve an inactivation effect on several bacterial and fungal species. Combinations with other disinfection methods often showed better results compared to separately applied methods. We therefore investigated contact lens disinfection solutions combined with 405 nm irradiation, with the intention to reduce the disinfectant concentration of ReNu Multiplus, OptiFree Express or AOSept while maintaining adequate disinfection results due to combination benefits. Pseudomonads, staphylococci and were studied with disk diffusion assay, colony forming unit (cfu) determination and growth delay. A log reduction of 4.49 was achieved for in 2 h for 40% ReNu Multiplus combined with an irradiation intensity of 20 mW/cm at 405 nm. For AOSept the combination effect was so strong that 5% of AOSept in combination with light exhibited the same result as 100% AOSept alone. Combination of disinfectants with visible violet light is therefore considered a promising approach, as a reduction of potentially toxic ingredients can be achieved.
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http://dx.doi.org/10.3390/ijerph17176422DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7504152PMC
September 2020

Selection of parameters for thermal coronavirus inactivation - a data-based recommendation.

GMS Hyg Infect Control 2020 13;15:Doc16. Epub 2020 Jul 13.

Pharmpur GmbH, Koenigsbrunn, Germany.

Healthcare workers and large parts of the population are currently using personal protective equipment, such as face masks, to avoid infections with the novel coronavirus SARS-CoV-2. This equipment must be sterilized as gently as possible before reuse. One possibility is thermal inactivation, but professional autoclaves with their high temperatures are often not available or suitable. If the inactivation period is long enough, coronavirus inactivation can also be carried out at relatively low temperatures. The required duration was determined in this study. Data from published thermal inactivation studies on coronaviruses were applied to determine the temperature dependence of the rate constant k(T) for each coronavirus by employing Arrhenius models. The data obtained exhibit large variations, which appear to be at least partially caused by different sample properties. Samples with high protein content or samples in dry air sometimes seem to be more difficult to inactivate. Apart from this, the Arrhenius models describe the thermal inactivation properties well and SARS-CoV and SARS-CoV-2 can even be represented by a combined model. Furthermore, the available data suggest that all samples, including critical ones, can be mathematically included by a worst-case Arrhenius model. Coronaviruses can already be inactivated at relatively low temperatures. For most samples, application times of approximately 32.5, 3.7, and 0.5 minutes will be sufficient at 60°C, 80°C, and 100°C, respectively, for a 5 log-reduction. For difficult conditions, the worst-case model provides significantly longer application times of 490, 55, and 8 minutes for the temperatures mentioned.
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http://dx.doi.org/10.3205/dgkh000351DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7373095PMC
July 2020

Realisation and assessment of a low-cost LED device for contact lens disinfection by visible violet light.

Biomed Tech (Berl) 2020 Aug;65(4):485-490

Ulm University of Applied Sciences, Institute of Medical Engineering and Mechatronics, Albert-Einstein-Allee 55, D-89081 Ulm, Germany.

This study presents a device for efficient, low-cost and eye-friendly overnight disinfection of contact lenses by visible violet light as an alternative to disinfection with biocide-containing solutions. Bacterial solutions with one Pseudomonas and one Staphylococcus strain each were irradiated for up to 8 h in commercial transparent contact lens cases by the presented light-emitting diode (LED) device. Samples were taken at different intervals and distributed on agar plates. The surviving bacteria were determined by counting of colony-forming units and compared to the specific requirements of the stand-alone test for contact lens disinfection of the hygiene standard ISO 14729. The concentration of both microorganisms was reduced by three orders of magnitude after less than 4 h of irradiation. The LED current and intensity have not yet been at maximum and could be further increased if necessary for other microorganisms. The presented device fulfils the requirement of the stand-alone test of the contact lens hygienic standard ISO 14729 for the tested Pseudomonas and Staphylococcus strains. According to literature data, the inactivation of Serratia marcescens, Candida albicans and Fusarium solani seems also possible, but may require increased LED current and intensity.
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http://dx.doi.org/10.1515/bmt-2019-0231DOI Listing
August 2020

Antimicrobial Effect of Visible Light-Photoinactivation of by Irradiation at 450, 470, and 620 nm.

Antibiotics (Basel) 2019 Oct 15;8(4). Epub 2019 Oct 15.

Ulm University of Applied Sciences, Department of Medical Engineering and Mechatronics, Albert-Einstein-Allee 55, D 89081 Ulm, Germany.

Despite the high number of legionella infections, there are currently no convincing preventive measures. Photoinactivation with visible light is a promising new approach and the photoinactivation sensitivity properties of planktonic to 450, 470, and 620 nm irradiation were thus investigated and compared to existing 405 nm inactivation data for obtaining information on responsible endogenous photosensitizers. Legionella were streaked on agar plates and irradiated with different doses by light emitting diodes (LEDs) of different visible wavelengths. When irradiating bacterial samples with blue light of 450 nm, a 5-log reduction could be achieved by applying a dose of 300 J cm, whereas at 470 nm, a comparable reduction required about 500 J cm. For red irradiation at 620 nm, no inactivation could be observed, even at 500 J cm. The declining photoinactivation sensitivity with an increasing wavelength is consistent with the assumption of porphyrins and flavins being among the relevant photosensitizers. These results were obtained for , but there is reason to believe that its inactivation behavior is similar to that of pathogenic legionella species. Therefore, this photoinactivation might lead to new future concepts for legionella reduction and prevention in technical applications or even on or inside the human body.
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http://dx.doi.org/10.3390/antibiotics8040187DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6963517PMC
October 2019

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

Photochem Photobiol 2020 01 22;96(1):156-169. Epub 2019 Oct 22.

Institute of Medical Engineering and Mechatronics, Ulm University of Applied Sciences, Ulm, Germany.

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 500 nm 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 415 nm could be explained by the involvement of zinc protoporphyrin IX. Between 450 and 470 nm, inactivation results indicated a broad plateau, statistically distinguishable from 440 and 480 nm. 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.
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http://dx.doi.org/10.1111/php.13168DOI Listing
January 2020

UV-C inactivation of Legionella rubrilucens.

GMS Hyg Infect Control 2017 10;12:Doc06. Epub 2017 Apr 10.

Ulm University of Applied Sciences, Ulm, Germany.

Despite the great health significance of , there is only little information on their UV sensitivity. Besides only has been investigated so far. In this study has been spread on buffered charcoal yeast extract agar and irradiated with the 254 nm UV-C emission of a mercury vapor lamp. The disinfection success is measured by colony counting after incubation and comparison of the number of colonies on irradiated and unirradiated reference agar plates. The average log-reduction dose is 1.08 mJ/cm for free , which is at the lower end of the so far published Legionella log-reduction values, but all three species show similar UV-C sensitivities. The log-reduction dose of legionellae in amoebae has not been investigated, but with the observed high UV-C sensitivity for free , the idea of a future point-of-use disinfection by small UV-C LEDs in water-taps or shower heads appears to be realistic, even if legionellae are more resistant in amoebae.
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http://dx.doi.org/10.3205/dgkh000291DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5388836PMC
April 2017

Improved contact lens disinfection by exposure to violet radiation.

Technol Health Care 2016 ;24(1):145-51

Background: Conventional procedures for contact lens disinfection, based on solutions with aggressive chemical ingredients, not only affect microorganisms but operate likewise damaging towards the epithelial eye surface.

Objective: The aim of this study was to evaluate the applicability of an alternative or complementary disinfection procedure for contact lenses based on irradiation within the visible wavelength range.

Methods: Suspensions of S. auricularis, B. subtilis and E. coli were exposed to 405 nm irradiation, for determining the disinfection efficacy. Surviving rates were analyzed by membrane filtration as well as a semi-quantitative analysis using DipSlides.

Results: A significant antibacterial effect of the 405 nm irradiation is verifiable for all probed bacteria. Using S. auricularis, there has been no colony forming after an irradiation exposure of 2 hours.

Conclusion: The hitherto existing results give reason for the assumption that violet LEDs integrated in contact lens cases will provide a subsidiary disinfection activity and maybe even offer the reduction of chemical ingredients in lens cleaning solutions to become gentler to the eye. In addition the danger of a rerise of the germ concentration after the completion of the disinfection procedure will be reduced.
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http://dx.doi.org/10.3233/THC-151104DOI Listing
January 2017