Inactivation of the multi-drug resistant pathogen Candida auris using ultraviolet germicidal irradiation (UVGI)

Candida auris, often a multi-drug resistant fungal pathogen, has become an emerging threat in healthcare settings around the world. Reliable disinfection protocols specifically designed to inactivate C. auris are essential, as many chemical disinfectants commonly used in healthcare settings have been shown to have variable efficacy at inactivating C. auris.

Ultraviolet germicidal irradiation (UVGI) was investigated as a method to inactivate clinically relevant strains of C. auris.

Ten C. auris and two C. albicans isolates were exposed to ultraviolet (UV) energy to determine the UV dose required to inactivate each isolate. Using a UV reactor, each isolate (10⁶ cells/mL) was exposed to 11 UV doses ranging from 10-150 mJ/cm² and then cultured to assess cell viability.

An exponential decay model was applied to each dose-response curve to determine inactivation rate constants for each isolate, which ranged from 0.108-0.176 cm²/mJ for C. auris and 0.239-0.292 cm²/mJ for C. albicans. As the model of exponential decay did not accurately estimate the dose beyond 99.9% inactivation, a logistic regression model was applied to better estimate the doses required for 99.999% inactivation. Using this model, significantly greater UV energy was required to inactivate C. auris (103 to 192 mJ/cm²) when compared to C. albicans (78 to 80 mJ/cm²).

This study demonstrated UVGI as a feasible approach for inactivating C. auris, although variable susceptibility among isolates must be taken into account. This dose-response data is critical for recommending UVGI dosing strategies to be tested in healthcare settings.