Variable sensitivity of clinical Candida auris strains to Biocides: implications for infection control in Healthcare Settings

Purpose: Candida auris, a multidrug-resistant yeast, poses significant challenges in healthcare settings due to its ability to form biofilms and resistance to common disinfectants. Understanding its susceptibility to biocides used in hospital disinfection practices is crucial for infection control. We investigated the biocide sensitivity of eight clinical C. auris strains from different patients and one reference strain (CDC B11903) using the biocide activity tests. Methods: Species identification was confirmed through MALDI-TOF MS, while clade differentiation and phylogenetic classification were determined via whole-genome sequencing. Biofilm formation was assessed using the MTT assay. Antifungal susceptibilities were tested according to CLSI standards. The effectiveness of biocides, including chlorine, chlorhexidine, and benzalkonium chloride, was evaluated through broth microdilution following CLSI standards and quantitative suspension and carrier tests, following EN standards. Results: All clinical strains were identified as clade 1, and the reference strain as clade 4, with all exhibiting biofilm formation. Clade 1 strains showed resistance to fluconazole, with MIC values ranging from 8 to 32 µg/ml, while being susceptible to other antifungals. Broth microdilution MIC assays for biocides demonstrated that all strains exhibited resistance to benzalkonium chloride. Chlorine and chlorhexidine showed variable efficacy, dependent on concentration and environmental cleanliness. Alcohol-based hand sanitizers demonstrated effectiveness against C. auris from the first minute of application. Conclusion: The study highlights the variable susceptibility of C.auris to different biocides, underscoring the challenge in eradicating this pathogen from healthcare environments. Our findings advocate for the careful selection of disinfectants in hospital settings, emphasizing the need for high-concentration chlorine and chlorhexidine solutions to combat C. auris, even in especially clean environments.