Tolerance of outbreak-associated Candida parapsilosis isolates to antiseptics in a dry surface biofilm model.

This study investigated the susceptibility of Candida parapsilosis clinical isolates, originally recovered from healthcare workers’ hands during a hospital outbreak, to commonly used hospital antiseptics under a dry surface biofilm (DSB) model. Unlike traditional hydrated biofilm systems, DSBs replicate low-moisture, nutrient-limited environments frequently encountered on hospital surfaces and medical devices. Over 12 days, monospecies DSBs were formed on glass coverslips and exposed for 3 min to seven antiseptics preparations, namely ethanol 70% (EtOH 70%), 0.5% alcoholic chlorhexidine (CHG 0.5%), 1% aqueous chlorhexidine (CHG 1%), 0.12% aqueous chlorhexidine (CHG 0.12%), 10% povidone-iodine (PVPI), 3% hydrogen peroxide (H2O2) and 70% isopropanol (IPA). Viability was assessed by log10 CFU/mL reduction, with ≥ 4 log10 considered microbiologically effective. EtOH 70% and CHG 0.5% consistently achieved > 5 log10 reductions, maintaining high activity despite desiccation. In contrast, PVP-I, IPA and CHG 0.12% showed poor performance (< 1 log10 median reduction), while 1% CHG 1% and H2O2 displayed intermediate efficacy. Hierarchical clustering revealed four distinct susceptibility phenotypes, suggesting intraspecific variability in tolerance to desiccation and biocides. Comparisons with previous hydrated biofilm data indicated reduced antiseptic efficacy under dry conditions, particularly for PVP-I. These results underscore the resilience of C. parapsilosis DSBs and highlight the need to revise disinfection protocols to address phenotypic diversity and persistence in clinical settings, especially on high-touch surfaces and invasive devices.