The efficacy of ozone-based automated room disinfection by STERISAFE PRO was tested against surfaces contaminated with the emerging multiresistant yeast Candida auris. The technology successfully reached a kill-rate above 4-log reduction under complex room conditions.

Candida auris is a yeast first described in 2009, and which has since then been involved in numerous healthcare-associated infections (HAI) across the world (CDC, 2019). It can cause serious cases of invasive candidiasis potentially leading to death, especially in hospitalized patients with weakened immune systems. This particular species of Candida fungi receives worldwide attention for its multiple drug resistance (MDR). Conventional antifungal medicines often have no effect for C. auris infection, and some infections have been reported to be resistant to all three major classes of antifungal agents (polyenes, azoles and echinocandins). Moreover, C. auris are easily misidentified as other Candida species by conventional laboratory methods, potentially leading to mismanagement of outbreaks in hospitals settings.

For those reasons, prevention is much more preferable than treatment for C. auris treatments. However, yeasts in general have a high survival rate on inanimate surfaces, and some C. auris strains have been shown to live on different surfaces for several weeks. Automated surface disinfection technology such as the one used by STERISAFE can prove useful to prevent the spread of C. auris in healthcare settings. Following a previously successful experimental setup with E. faecium in real-life conditions, Knobloch et al. (2019) repeated their experiments with C. auris, and investigated the efficacy of a STERISAFE PRO in a hospital patient room.

For this test, Knobloch et al. used four C. auris strains, with two particular strains chosen for their high ability to survive under adverse conditions. To confirm yeasticidal activity, an innocuous strain of Candida albicans was also included. While the rest of the general experimental design mostly remained unchanged, this time the different strains of the pathogen of interest were placed on different surface types: ceramic tiles, stainless steal and solid core furniture board (see Figure 1). The contaminated surfaces were first dried, then placed in eight different positions in the main room and adjacent rooms (bathroom and vestibule). Microbial testing was done after a standard STERISAFE PRO disinfection cycle (80 ppm ozone, 60 min dwell time, 90% R.H., 150 min total) and the experiment was triplicated for quality control purposes. Both the kill-rate and the survival capacity were assessed.

During the drying step prior to the STERISAFE PRO treatment, the different C. auris strains showed varied survivability rates. Out of the four tested strains, one died off rapidly during drying, another displayed a significant cell counts reduction. Only the two strains chosen for their high resistance to adversity exhibited sufficient cell counts for further disinfection analyses; they were submitted to ozonation under the STERISAFE PRO treatment, along with C. albicans. The three yeasts strain investigated shown an average reduction rate above 4-log reduction after the standard ozonation cycle, which is compliant with the strict requirements of the NF T 72-281 standard. This test demonstrates that STERISAFE PRO attains sufficient yeasticidal activity for the tested C. auris strains. But the difference in survival behaviour between the different C. auris strains calls for some care concerning potentially more resistant strains.

Figure 1. Inanimate surface materials used for contamination before survival and disinfection experiments (reproduced with courtesy of Knobloch et al., 2019)


  1. Knobloch J.K., Franke G., Belmar Campos C.E., Klupp E.M., Voss A. & Meis J.F. (2019). Disinfection of surfaces contaminated with Candida auris using ozone under complex room conditions. Mycoses 62 (S1): 29
  2. CDC, Center for Disease Control and Prevention (2019). Candida auris. U.S. Department of Health & Human Services, accessed October 2019. <>