Effect of exposure time and distance on UV-C dependent killing of Candida auris
This fungus is associated with hospital outbreaks throughout the world. They display variable antifungal susceptibility profiles and develop resistance quickly.
This has been a major hurdle to infection prevention and control.
Invasive infection and colonization occur in critically ill patients in intensive care units. Increased prophylactic use of fluconazole has led to the emergence of multi-drug resistance patterns in Candida albicans and non-albicans Candida species. Skin colonization and inanimate surface contamination contribute to patient to patient transmission of C.auris. Skin decolonization and decontamination of hospital surfaces are crucial steps in controlling C.auris outbreaks. Different healthcare organizations suggest the use of different agents for disinfection. Some studies have documented the effectiveness of hydrogen peroxide vapours. Another popular approach in decontamination of hospital surfaces is the use of mobile Ultraviolet-C devices. Public Health England encourages the use of UV-C in addition to manual disinfection procedures for tackling the spread of C.auris. Hospital rooms vary in size and design. Factors like exposure time and distance from the UV-lamp are important parameters to consider for a successful room decontamination. This study compares the UV-C sensitivity of C.auris strains originating from Venezuela, Spain, India and Japan/Korea to that of Candida albicans.
To make sure, how to successfully decontaminate C.auris in the shortest period of time, the experiment was made, using motion-sensor enabled UV-C robot, that followed to next important conclusions:
a.) At 20-30 minutes of UV-C exposure, a 10-fold increase in fungal concentration reduces the effectivity of UV-C treatment by 10-fold.
b.) Maximum effect was obtained by 30 minutes of exposure at 2m distance from the UV-C source.
The procedure of conducting the experiment
Stock of each strain of fungus was suspended in phosphate buffer saline and a 20µl suspension of each strain containing 1x105 or 2x106 colony forming units (CFUs) were spread on multitest glass slides and allowed to air dry at 35°C in an incubator for 30-40 minutes. These multitest slides were used as samples for the experiment.
The experiments were carried out in a 3x5m standard laboratory room, where the samples were placed on a table at a distance of 2 or 4m from the UV-C device. The samples were exposed to UV-C radiations for 5, 10, 20 or 30 minutes. Control slides were tested in the same manner except without exposure to UV-C. The cells from the slide were resuspended in PBS and transferred to Sabouraud dextrose agar plates for incubation at 35°C for 24-48 hours.
Seeding density, time of exposure and distance from UV-C source affected UVC efficacy of each strain of C.auris.
Figure 1A. Log10 CFU reduction at different seeding concentrations and exposure time (Groot, Chowdhary, Meis, & Voss, 2019).
C.auris seeded at 1x105 CFU displayed a higher significant time-dependent reduction (Figure 1A) in CFU as compared to those seeded at 1x106 CFU when distance from the UVC source was fixed.
Figure 1B: Log10 CFU reduction as a function of distance (Groot, Chowdhary, Meis, & Voss, 2019).
Increasing the distance from the UV source reduced the efficacy of UV-C killing (Fig 1B).
Comparison of C auris strains revealed that strains from Japan and Korea were more susceptible to UV-C disinfection than those from Spain, Venezuela and India.
Groot, T. D., Chowdhary, A., Meis, J. F., & Voss, A. (2019). Killing of Candida auris by UV-C: Importance of exposure time and distance. Mycoses, 62(5), 408–412. doi: 10.1111/myc.12903