Resistance Development in Escherichia coli Against Far-UVC Irradiation

Abstract Nosocomial pathogens spread in hospitals and are a permanent issue to patient safety [1]. Disinfecting medicinal equipment is therefore most important. Usually, chemical disinfection is applied but time consuming. Another known disinfection technique is irradiation with wavelength below 280 nm (UVC). UVC efficiently inactivates pathogens but usually cannot be applied in the presence of humans. The recently emerging Far-UVC with wavelengths between 200 and 230 nm is assumed to pose no danger to humans and is considered to be applied more frequently in the future. Therefore, this study investigates the potential radiation resistance development of Escherichia coli K12 caused by repeated exposure to 222 nm Far-UVC irradiation and the persistence of these adaptations. A cyclic irradiation experiment was conducted over ten cycles, followed by the assessment of resistance persistence over four subsequent cycles. The sensitivity of bacteria to irradiation was analyzed for exposure durations of 5, 10 and 15 seconds at an irradiation intensity of 1 mW/cm2. The number of the bacteria after the incubation between the cycles after a fixed incubation time and morphological changes in bacteria colonies on Luria-Bertani (LB) plates were observed, indicating potential adaptation mechanisms. The results indicate that cyclic irradiation with this amount of irradiation intensity and the duration of several seconds does not induce significant and persistent Far-UVC radiation resistance but suggests transient adaptive responses which are not permanent. Adaptive reactions must be investigated more closely to avoid creating additional radiation resistance to existing drug resistances