Skin tolerant inactivation of multiresistant pathogens using far-UVC LEDs

Abstract

Multiresistant pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) cause serious postoperative infections. A skin tolerant far-UVC (< 240 nm) irradiation system for their inactivation is presented here. It uses UVC LEDs in combination with a spectral filter and provides a peak wavelength of 233 nm, with a full width at half maximum of 12 nm, and an irradiance of 44 µW/cm². MRSA bacteria in different concentrations on blood agar plates were inactivated with irradiation doses in the range of 15-40 mJ/cm². Porcine skin irradiated with a dose of 40 mJ/cm² at 233 nm showed only 3.7% CPD and 2.3% 6-4PP DNA damage. Corresponding irradiation at 254 nm caused 15-30 times higher damage. Thus, the skin damage caused by the disinfectant doses is so small that it can be expected to be compensated by the skin's natural repair mechanisms. LED-based far-UVC lamps could therefore soon be used in everyday clinical practice to eradicate multiresistant pathogens directly on humans.

Figure 1

(a) Voltage, wall-plug efficiency and optical power as a function of current of a typical flip-chip mounted 233 nm LED used in the irradiation module. (b) Emission spectrum of the LED operated at 20 mA. (c) Image of a 233 nm LED flip-chip mounted on a Si-cavity surface-mounted device package (footprint = 3.5 mm × 3.5 mm). (d) Far-field radiation distribution measured of a typical 233 nm LED operated at 20 mA.

Figure 2

(a) Picture of the completely assembled far-UVC LED irradiation system where the radiation unit with the LEDs and the vertical and slanted reflectors are visible. (b) Half of a cross section schematic of the optical components of the far-UVC LED radiation unit. (c) Simulated (blue curve, solid line) and measured (red curve, dashed line) transmission spectra of the DBR filter under normal incidence. (d) Emission spectra measured at the maximum operation current of the LEDs (100 mA), at a distance of 25 mm from the lower edge of the vertical reflector and at five different positions (center (Pos. 1) and four corners of the LED array (Pos. 2–5)). (e) and (f) The irradiance distribution of the far-UVC LED irradiation system on a 70 mm × 70 mm target area measured (e) without and (f) with the DBR filter at the maximum operation current of the LEDs (100 mA) and at a distance of 25 mm from the lower edge of the system. In both cases the uniformity (defined as 100% − (standard deviation/mean value of the irradiance)) is > 90%.

Figure 3

Columbia blood agar plates inoculated with different concentrations of bacterial suspension (MRSA, DSM 11822) without and with UVC irradiation for different times using either far-UVC (233 nm) or near-UVC (254 nm) radiation and after incubation for 24 h. The numbers below the plates indicate the applied UV dose.

Figure 4

(a) DNA damage for irradiated porcine skin using 254 nm and 233 nm light sources with 40 mJ/cm². Untreated skin served as control. The mean values of the epidermal DNA damage in % are calculated from at least three experiments and the error bars show the standard error of the mean. (b)–(e) Histologic images HE and CPD stained porcine skin after irradiation using the far-UVC LED irradiation system without (c) and with filter (d), in comparison, untreated skin (e) and skin after irradiation with near-UVC radiation at 254 nm (f). Arrows mark CPD positive cells. The scale bar is 100 µm.