In the Right Light: Photodynamic Inactivation of Microorganisms Using a LED-Based Illumination Device Tailored for the Antimicrobial Application

Abstract

Drug-resistant bacteria threaten the health of people world-wide and cause high costs to their health systems. According to Scientific American, the number of regrettable fatalities due to the bacteria that are resistant to conventional antibiotics will sum up to 300 million until 2050 if the problem is not tackled immediately. Photodynamic Inactivation (PDI) has proven effective against microorganisms irrespective of their resistance to conventional treatment, but for the translation into clinical practice, economic, homogenous and powerful light sources holding approval as medical devices are needed. In this study we present two novel light emitting diode (LED)-based lamps (Repuls7PDI-red and Repuls7PDI-blue) tailored for application in PDI and demonstrate their photodynamic efficiency upon using either methylene blue (MB), a photoactive compound widely used in PDI, or Sodium Magnesium Chlorophyllin (CHL), a water-soluble derivative of chlorophyll, which holds approval as food additive E140, against bacteria and fungi. Gram+ Staphylococcus aureus, Gram− Escherichia coli and the yeast Candida albicans serve as model systems. Repuls7PDI-red emits a wavelength of 635 nm and an intensity of 27.6 ± 2.4 mW·cm−2 at a distance of 13.5 cm between the light source and the target, while the Repuls7PDI-blue allows an exposure at 433 nm (within the range of violet light) (6.4 ± 0.5 mW·cm−2 at 13.5 cm). Methylene blue was photoactivated with the Repuls7PDI-red at 635 nm (25.6 J·cm−2) and allows for photokilling of E. coli by more than 6 log10 steps at a concentration of 10 µM MB. Using equal parameters, more than 99.99999% of S. aureus (20 µM MB) and 99.99% of C. albicans (50 µM MB) were killed. If blue light (Repuls7PDI-blue, 433 nm, 6.6 J·cm2) is used to trigger the production of reactive oxygen species (ROS), a photoinactivation of S. aureus (5 µM CHL, CFU reduction > 7 log10) and C. albicans (>7 log10) below the detection limit is achieved. PDI based on CHL (10 µM) using red light activation reduces the number of viable S. aureus by more than 6 log10. Our data prove that both LED-based light sources are applicable for Photodynamic Inactivation. Their easy-to-use concept, high light output and well-defined wavelength might facilitate the translation of PDI into clinical practice.

Inactivation efficacy of 405 nm light emitting diodes (LEDs) on Salmonella Enteritidis at different illumination temperatures

“…Light emitting diodes (LEDs) technologies have become increasingly feasible and advantageous in potential applications of the food industry due to its low radiant heat emissions, long life expectancy, flexibility and mechanical robustness (D'Souza et al, 2015). Photodynamic inactivation (PDI), based on the use of photosensitizers activated by an appropriate wavelength light, utilizes the photosensitizermediated and light-induced overproduction of reactive oxygen species (ROS) to inactivate the foodborne and food spoilage bacteria (Penha et al, 2017;Hasenleitner & Plaetzer, 2019). A light source of suitable wavelength, photosensitizer and oxygen are the essential components for the PDI .…”

Photodynamic disinfection and its role in controlling infectious diseases

“…The interest in relatively large field illuminations for PDDI of skin infections motivated the development of LED devices tailored for methylene blue (635 ± 11.5 nm) and for sodium magnesium chlorophylin (433 ± 10.5 nm) [ 302 ]. This later dye is a food additive and is of interest for the photodisinfection of food.…”

Photodynamic inactivation of planktonic Staphylococcus aureus by sodium magnesium chlorophyllin and its effect on the storage quality of lettuce

“…Sodium magnesium chlorophyllin (SMC), a derivative of chlorophyll, has many advantages, such as good water solubility, high affinity to biomolecules, excellent photosensitivity and rapid elimination from the body with no adverse reactions. In addition, it is reported that PDI based on SMC (10 µmol/L) reduced the number of viable S. aureus by more than 6 log CFU/ mL [20]. Therefore, SMC has potential application as a photosensitizer used in PDI to eradicate pathogens on food products.…”