Clade-specific variation in susceptibility of Candida auris to broad-spectrum ultraviolet C light (UV-C)

Candida auris is an emerging and often multidrug-resistant fungal pathogen with an exceptional ability to persist on hospital surfaces. These surfaces can act as a potential source of transmission. Therefore, effective disinfection strategies are urgently needed. We investigated the efficacy of ultraviolet C light (UV-C) disinfection for C. auris isolates belonging to 4 different clades.

In vitro testing of C. auris isolates was conducted using 106 colony-forming units (CFU) spread on 20-mm diameter steel carriers and exposed to a broad-spectrum UV-C light source for 10, 20, and 30 minutes at a 1.5 m (5 feet) distance. Post-UV survivors on the coupons were subsequently plated. Colony counts and log reductions were recorded, calculated, and compared to untreated control carriers. Identification of all isolates were confirmed by MALDI-TOF and morphology was visualized by microscopy.

We observed an increased susceptibility of C. auris to UV-C in 8 isolates belonging to clades I, II and IV with increasing UV exposure time. The range of log kill (0.8-1.19) was highest for these isolates at 30 minutes. But relatively no change in log kill (0.04-0.35) with increasing time in isolates belonging to clade III were noted. Interestingly, C. auris isolates susceptible to UV-C were mostly nonaggregating, but the isolates that were more resistant to UV exposure formed aggregates.

Our study suggests variability in susceptibility to UV-C of C. auris isolates belonging to different clades. More studies are needed to assess whether a cumulative impact of prolonged UV-C exposure provides additional benefit.