UV radiation sensitivity of bacteriophage PhiX174- A potential surrogate for SARS-CoV-2 in terms of radiation inactivation

To minimize health risks, surrogates are often employed to reduce experiments with pathogenic microorganisms and the associated health risk. Due to structural similarities between the enveloped RNA -viruses SARS-CoV-2 and Phi6, the latter has been established as a nonpathogenic coronavirus surrogate for many applications. However, large discrepancies in the UV log-reduction doses between SARS-CoV-2 and Phi6 necessitate the search for a better surrogate for UV inactivation applications. A literature study provided the bacteriophage PhiX174 as a potentially more suitable nonpathogenic coronavirus surrogate candidate. In irradiation experiments, the sensitivity of PhiX174 was investigated upon exposure to UV radiation of wavelengths 222 nm (Far-UVC), 254 nm (UVC), 302 nm (broad-band UVB), 311 nm (narrow-band UVB) and 366 nm (UVA) using a plaque assay. The determined log-reduction doses for PhiX174 were 1.3 mJ/cm2 @ 222 nm, 5 mJ/cm2 @ 254 nm, 17.9 mJ/cm2 @ 302 nm, 625 mJ/cm2 @ 311 nm and 42.5 J/cm2 @ 366 nm. The comparison of these results with published log-reduction doses of SARS-CoV-2 in the same spectral region, led to the conclusion that the bacteriophage PhiX174 exhibits larger log-reduction doses than SARS-CoV-2, nevertheless, it is a better UV-surrogate at 222 nm (Far-UVC), 254 nm (UVC) and 302 nm (UVB) than the often applied Phi6.

Surface disinfection with white-violet illumination device

The spread of infections, as in the coronavirus pandemic, leads to the desire to perform disinfection measures even in the presence of humans. UVC radiation is known for its strong antimicrobial effect, but it is also harmful to humans. Visible light, on the other hand, does not affect humans and laboratory experiments have already demonstrated that intense visible violet and blue light has a reducing effect on bacteria and viruses. This raises the question of whether the development of pathogen-reducing illumination is feasible for everyday applications. For this purpose, a lighting device with white and violet LEDs is set up to illuminate a work surface with 2,400 lux of white light and additionally with up to 2.5 mW/cm2 of violet light (405 nm). Staphylococci are evenly distributed on the work surface and the decrease in staphylococci concentration is observed over a period of 46 hours. In fact, the staphylococci concentration decreases, but with the white illumination, a 90% reduction occurs only after 34 hours;with the additional violet illumination the necessary irradiation time is shortened to approx. 3.5 hours. Increasing the violet component probably increases the disinfection effect, but the color impression moves further away from white and the low disinfection durations of UVC radiation can nevertheless not be achieved, even with very high violet emissions.

Development and verification of a test rig for inactivation of bacteria and (corona-) viruses by UVC air disinfection systems

The ongoing coronavirus pandemic spreads through airborne transmission and is therefore difficult to contain. However, coronaviruses are highly sensitive to UVC, so UVC air disinfection systems should be able to inactivate the virus. Unfortunately, so far there are only few possibilities to test the reduction of airborne viruses or other pathogens. A special test rig, which mainly consisted of a nebulizer and an airflow system, was developed to determine the antiviral and antibacterial efficiency of UVC air disinfection systems. In the assessment of such an UVC air disinfection system with nebulized Staphylococcus carnosus and a sampling period of 30 minutes, a mean bactericidal reduction of 3.70 log10 (99.98 %) was determined. For antiviral irradiation of the coronavirus surrogate phi6 a mean viral load reduction of 1.18 log10 (93.40 %) was observed after a sampling period of 10 minutes. Therefore, mobile UVC air disinfection systems could be applied in hospitals, retirement and nursing homes. © 2021 by Walter de Gruyter Berlin/Boston.

Minimum irradiance required to inhibit microbial growth to prevent ventilatorassociated pneumonia by an endotracheal tube equipped with blue LEDs

Artificial respiration is saving lives especially in the COVID-19 pandemic, but it also carries the risk to cause ventilator-Associated pneumonia (VAP). VAP is one of the most common and severe nosocomial infections, often leading to death and adding a major economic burden to the healthcare system. To prevent a proliferation of microbial pathogens that cause VAP, an endotracheal tube (ETT) equipped with blue LEDs (LED-ETT) was developed. This blue wavelength exhibits antimicrobial properties but may also harm human tracheal cells at higher irradiances. Therefore, the aim of this study was to find the minimal required irradiance for microbial reduction of 1 log level in 24 h by applying LED-ETTs. A LED-ETT with 48 blue LEDs (450 nm) was fixed in a glass tube, which served as a trachea model. The investigation was carried out with irradiations of 4.2, 6.6 and 13.4 mW/cm² at 37 °C for 24 h. The experiments were performed with Acinetobacter kookii as a surrogate of Acinetobacter baumannii, which is classified as critical by the WHO. Samples of A. kookii suspensions were taken every 4 h during irradiation from the trachea model. Bacteria concentrations were quantified by determining colony forming units (CFU)/ml. A homogeneous irradiance of only 4.2 mW/cm² generated by the blue LEDs, at a LED forward current of 3.125 mA, is sufficient to achieve a 1 log reduction of A. kookii within 24 h. The total irradiation dose within this period was 360 J/cm2. Human cells survive this dose without cellular damage. Previous studies revealed that the pathogen A. baumannii is even more sensitive to blue light than A. kookii. Therefore, blue LED-ETTs are expected to reduce A. baumannii without harming human tracheal cells. © 2021 by Walter de Gruyter Berlin/Boston.

Minimum irradiance required to inhibit microbial growth to prevent ventilator-associated pneumonia by an endotracheal tube equipped with blue LEDs

Introduction Artificial respiration is saving lives especially in the COVID-19 pandemic, but it also contains the risk to cause ventilatorassociated pneumonia (VAP). VAP is one of the most common and severe nosocomial infections often leading to death and adding a major economic burden to the healthcare system. To prevent a proliferation of microbial pathogens that cause VAPs, an endotracheal tube equipped with blue LEDs (LED-ETT) was developed. This blue wavelength exhibits antimicrobial properties but may also harm human tracheal cells. Therefore, the aim of this paper was to find the minimal required irradiance for microbial reduction of 1 log level in 24 h by applying LED-ETTs. Methods A LED-ETT with 48 blue LEDs (450 nm) was fixated in a glass tube, which functions as a trachea model. The investigation was carried out with irradiations of 4.2, 6.6 and 13.4 mW/cm2 at 37 °C for 24 h. The experiments were performed with Acinetobacter kookii as a surrogate of Acinetobacter baumannii, which is classified as critical by the WHO. Samples of A. kookii suspensions were taken every 4h during irradiation from the trachea model. Bacteria were quantified by determining colony forming units cfu/ml. Results A homogeneous irradiance of only 4.2 mW/cm2 generated by the blue LEDs, at a current of 25 mA, is sufficient to achieve a 1 log reduction of A. kookii within 24 h. The total irradiation dose within this period was 360 J/cm2. Conclusion 360 J/cm2is a dose that human cells survive without cellular damage. Previous studies revealed that the pathogen A. baumannii is even more sensitive to blue light. Therefore, blue LED-ETTs are expected to reduce A. baumannii without harming human tracheal cells.

Development and verification of a test rig for inactivation of bacteria and (corona-) viruses by UVC air disinfection systems

Introduction The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), continues to spread and has so far resulted in over 166 million confirmed infections and more than 3.44 million deaths worldwide. The virus propagates mainly through the air and therefore UVC air disinfection systems should be able to deliver a major contribution to containing the pandemic. There is increasing evidence that coronaviruses are highly sensitive to UVC, but so far there are only few possibilities to test the reduction of airborne viruses. Should the presumed antiviral efficacy against coronaviruses be confirmed, mobile UVC air disinfection systems could be applied in hospitals, retirement and nursing homes, as well as in public healthcare institutions. Methods A special test rig, which mainly consisted of a nebulizer and an airflow system, was developed to determine the antiviral and antibacterial efficiency of UVC air disinfection system. Due to regulatory issues the coronavirus surrogate phi6 and Staphylococcus carnosus, a non-pathogenic relative of the Methicillin-resistant Staphylococcus aureus, were investigated by double agar plaque assay and plate count method. Results In irradiation experiments with nebulized S. carnosus and a latency period of 30 minutes, a mean bactericidal reduction of 3.70 log (99.98 %) was determined. Compared to the unirradiated reference, the decrease caused by the UVC irradiation was 2.59 log (99.74 %). For the antiviral irradiation of the coronavirus surrogate phi6 a mean viral load reduction of 1.18 log (93.40 %) was observed for the examined UVC air disinfection system after a latency period of 10 minutes. After subtracting the unirradiated reference, the mean decrease in the corona-like virus was 0,83 log (85.10 %). Conclusion The developed test rig is therefore, capable to prove and even quantify the reduction of airborne pathogens by UVC air disinfection systems including coronavirus surrogates and probably even coronaviruses.