Importance of Ultraviolet-C (UV-C) Emitter Configuration for the Attenuation of Staphylococcus aureus and Candida...

The relative importance of different ultraviolet-C (UV-C) emitter configurations on the attenuation of vegetative bacterial and fungal pathogens has not been assessed. We hypothesized that emitter configuration would impact the efficacy of UV-C attenuation of Staphylococcus aureus ( S. aureus) and Candida auris (C. auris) pathogens.

American Type Culture Collection (ATCC) S. aureus (ATCC 6538) and C. auris (ATCC MYA-5001) carriers (ReadyNowTM Test Carriers, Stratix Labs Corporation, Saint Paul, MN) were mounted on an aluminum stand along with three calibrated radiometers (International Light Technologies model ILT1270, Peabody, MA). Five UV-C emitter configurations were assessed, including three emitters with a triangular configuration about the stand and each rotating 360° (1), one emitter facing the stand and rotating 360° (2), three emitters facing the stand in a linear configuration and each rotating 5° (3), one emitter facing the stand and rotating 5° (4), and one emitter facing the stand and rotating 90° (5). Three serial experiments were conducted. The first experiment involved the establishment of the minimally effective irradiation dose (mean and standard deviation mJ/cm²) required to achieve no growth (6-log reduction (LR)) with direct exposure to pathogen carriers positioned at the center of the lamp. We then assessed the relative efficacy of delivery of the minimally effective dose via the five emitter configurations in attenuating polycarbonate and textured pathogen carriers. Polycarbonate carriers were positioned at 25.5 and 69.5 inches from the floor and oriented vertically to the emitters. Textured plastic pathogen carriers were positioned at 47.5 or 58.5 inches from the floor and with a 45° or horizontal orientation to the emitters. Standard carriers (1"x0.9") were used for both pathogens and large carriers (1"x3") for C. auris,the latter to address the potential for cell clustering.

With standard carriers, the minimally effective dose was 27.01± 0.15 mJ/cm² for S. aureus but was not achieved for C. auris. The minimally effective dose for large C. auris carriers was 596.62 ± 27.98 mJ/cm². With standard carriers, all configurations achieved a >6 log reduction for S. aureus, and none achieved a >6 log reduction for C. auris. All configurations achieved a > 6 log reduction when 596.62 ± 27.98 mJ/cm² was delivered to large C. auris carriers. Changing to textured plastic carriers (standard for S. aureus and large for C. auris) and varying height (47.5-69.5 inches) from the floor and orientation to the emitters (45° and horizontal), the mean ± standard deviation for S. aureus and C. auris log reductions with delivery of the minimally effective dose was 4.44 ± 2.02, 2.58 ± 2.37, 3.55 ± 2.67, 2.33 ± 2.47, and 3.00 ± 2.64 for configurations one through five, respectively. Configuration one achieved a significantly greater LR than configurations two (adjusted P = 0.0018) and four (adjusted P = 0.023). There were 22% (6/27) of sites ≥ 100 colony-forming units (CFU) following cleaning but before UV-C vs. 0% (0/27) of sites ≥ 100 CFU after surface disinfection cleaning and nine minutes of configuration three UV-C treatment (P = 0.023).

The choice of UV-C emitter configuration can impact S. aureus and C. auris attenuation when there is indirect exposure to the pathogen. Emitter configuration should be considered as an important parameter for future UV-C technological assessments.