Abstract Description

Fungal infections pose a significant global health threat, particularly in immunocompromised individuals such as those living with HIV/AIDS, cancer, or organ transplants. These infections affect over 300 million people annually, causing more than 1.5 million deaths. In South Africa, the burden is amplified by the overlapping epidemics of HIV, tuberculosis, and poverty, yet fungal diseases remain under-prioritised in national health policies. Candida albicans remains the most common cause of invasive candidiasis, owing to its ability to undergo morphological changes and form drug-resistant biofilms. In parallel, Candida auris, a recently emerged multidrug-resistant species, has become a major global concern due to its persistence in healthcare settings and high levels of antifungal resistance. Conventional antifungal treatments are often ineffective against biofilms, necessitating the search for novel agents. Phenothiazines (PTZs), originally developed as antipsychotic drugs, have shown potential antifungal activity, including disruption of biofilms and synergy with standard antifungals. This study aimed to assess the antifungal activity and potential mechanisms of action of five commercial PTZs against Candida biofilms. Minimum inhibitory concentrations (MICs) were determined for biofilms of C. albicans and C. auris. Biofilm biomass and metabolic activity were quantified using crystal violet and XTT assays. Sub-MIC concentrations were then used to examine changes in biofilm morphology (via scanning electron microscopy), synergy with fluconazole, lipid content, germ tube formation, hyphal elongation, mitochondrial membrane potential, and reactive oxygen species (ROS) levels. CPZ and PMZ significantly reduced metabolic activity and disrupted biofilm structure. Both compounds exhibited synergistic effects with fluconazole. Treatment also led to a decrease in total lipid content, suggesting membrane disruption or interference with lipid biosynthesis. All PTZs reduced mitochondrial membrane potential and ROS production, with the most pronounced effect observed in FPZ-treated cells. These findings highlight the potential of PTZs as adjunctive antifungal agents targeting biofilm-associated resistance mechanisms in Candida.