Morphological, metabolic, and chemical changes in Candida albicans cells induced by the NaQSA complex

Abstract

This study examines the effects of the sodium complex of quercetin-5′-sulfonic acid (NaQSA) on Candida albicans yeast cells. Flow cytometric analysis showed a concentration-dependent decrease in viable cell numbers after incubation with NaQSA, indicating reduced cellular viability in treated cultures. Fluorescence microscopy revealed marked alterations in cell wall organization. Cells exposed to NaQSA displayed increased fluorescence intensity with Calcofluor White and Congo Red staining, especially in intercellular septa and division scars. Morphological abnormalities were common, including cell deformation, aggregation, and the formation of chains of incompletely separated daughter cells. These findings were supported by scanning electron microscopy, which confirmed substantial cell surface deformations and defects in cell division. Further nanoscale characterization by atomic force microscopy showed significant changes in surface topography and nanomechanical properties of treated cells, including increased surface roughness, elasticity, and deformation. Fourier-transform infrared (FTIR) spectroscopy revealed distinct changes in the chemical composition of the cell walls depending on NaQSA dose compared to control cultures. Specifically, spectral data showed a gradual increase in the relative cell wall lipid content following NaQSA exposure. A similar effect was observed for polysaccharides, including the absorption bands of β-1,3-glucan and α-mannan fibers that form the outer protective layer. In contrast, decreased intensity of the amide I and II bands suggested a reduction in glycoprotein content. Importantly, NaQSA did not cause cytotoxic or cytopathic effects in human fibroblasts, indicating selective activity toward fungal cells. These findings suggest that NaQSA significantly affects the structural and biochemical properties of the C. albicans cell wall, supporting its potential for further biomedical applications.