Identification of sialic acids on the cell surface of Candida albicans

The cell-surface expression of sialic acids in two isolates of Candida albi cans was analyzed by thin-layer and gas chromatography, binding of lectins, colorimetry, sialidase treatment and flow cytofluorimetry with fluorescein -labeled lectins. N-acetylneuraminic acid (NANA) was the only derivative fo und in both strains of C. albicans grown in a chemically defined medium. It s identification was confirmed by mass spectrometry in comparison with an a uthentic standard. The density of sialic acid residues per cell ranged from 1.6x10(6) to 2.8x10(6). The surface distribution of sialic acids over the entire C. albicans was inferred from labeling with fluorescein-Limulus poly phemus and Limax flavus agglutinins and directly observed by optical micros copy with (FITC)-Sambucus nigra agglutinin (SNA), abrogated by previous tre atment of yeasts with bacterial sialidase. Sialidase-treated yeasts generat ed beta-galactopyranosyl terminal residues that reacted with peanut aggluti nin. In C. albicans N-acetyl-neuraminic acids are alpha 2,6- and alpha 2,3- linked as indicated by yeast binding to SNA and Maackia amurensis agglutini n. The alpha 2,6-linkage clearly predominated in both strains. We also inve stigated the contribution of sialic acids to the electronegativity of C. al bicans, an important factor determining fungal interactions in vivo. Adhesi on of yeast cells to a cationic solid phase substrate (poly-L-lysine) was m ediated in part by sialic acids, since the number of adherent cells was sig nificantly reduced after treatment with bacterial sialidase. The present ev idence adds C. albicans to the list of pathogenic Fungi that synthesize sia lic acids, which contribute to the negative charge of fungal cells and have a role in their specific interaction with the host tissue. (C) 2000 Elsevi er Science B.V. All rights reserved.