Cellular and material-specific responses of Candida parapsilosis biofilms to biocides

Candida parapsilosis biofilms pose significant challenges in clinical settings due to their resilience to biocides and the presence of persister cells. This study evaluated the efficacy of amphotericin B (AmB), chlorhexidine (CLX), and ortho-phthalaldehyde (OPA) against biofilms formed by fluconazole-resistant C. parapsilosis isolates and examined the role of persister cells and catheter materials in biofilm resilience.

Clinical isolates of C. parapsilosis from hospital surfaces were exposed to CLX (0.5%) and OPA (0.55%). Minimum inhibitory concentrations (MICs) were determined by broth microdilution. Biofilm susceptibility was assessed using the crystal violet assay and total plate counts. Scanning electron microscopy (SEM) analysed biofilm structural changes on different catheter materials.

AmB demonstrated high efficacy with low MIC and MFC values. CLX showed moderate efficacy, with higher MICs and MFCs in clinical isolates compared with the standard strain. OPA exhibited the lowest efficacy, with higher MIC, MFC, and SMIC₈₀ values. Persister cells were confirmed in isolate CBL 1031, while isolates 17D, 26E, and ATCC 90019 displayed significant SMIC80 reductions, indicating high susceptibility. PTFE materials showed significant biofilm reductions post-biocide exposure, while HDPE displayed the greatest biofilm resilience with higher residual cell counts. SEM revealed material-specific biofilm disruption, with greater structural damage on HDPE and silicone-coated latex (SCL) compared with PTFE.

These findings underscore the importance of optimizing cleaning protocols, selecting appropriate medical materials, and addressing persister cells to mitigate biofilm-related infections in healthcare settings.