Disinfectant tolerance of Candidozyma auris and Candida albicans biofilms evaluated using the bead assay for biofilms

Abstract

Candidozyma auris (formerly Candida auris) has emerged as a critical nosocomial pathogen, notable for its multidrug resistance and its capability to form biofilms that enable persistence on surfaces. Although effective disinfection strategies are urgently needed, current disinfectant efficacy standards in many regions, such as Europe, are primarily based on testing planktonic Candida albicans and do not adequately reflect the resilience of Candida biofilms, including those of C. albicans and C. auris. To address this gap, the Bead Assay for Biofilms, previously developed for bacterial biofilms, was adapted for the first time to eukaryotic cells. The goal was to cultivate C. auris and C. albicans biofilms and evaluate the efficacy of selected disinfectants across four active substance classes. Cell enumeration demonstrated highly reproducible biofilms, whose architecture was confirmed by scanning electron microscopy. Both an alcohol- and a QAC-based product did not achieve sufficient reduction of at least ≥4 log10 CFU/mL of biofilm-cells when applied under conditions recommended by the manufacturer (alcohol 1 min: C. auris 0.82, C. albicans 0.54; QAC 1%, 15 min: C. auris 1.94, C. albicans 0.68). This reduced efficacy is consistent with the known increased tolerance of microorganisms in biofilms. In contrast, peracetic acid and glutaraldehyde achieved sufficient reductions, albeit at relatively high concentrations (peracetic acid 0.1%: C. auris 4.75 and 0.05%: C. albicans 4.87; glutaraldehyde 0.5%: C. auris 5.32 and C. albicans 4.15). Our findings underscore the need to adapt disinfection protocols and testing models to consider biofilm formation of C. auris and C. albicans, and species-specific resilience.