Susceptibility and resistance of Candida to 5-fluorocytosine in relation to the cell wall ultrastructure.

Studies on the susceptibility of Candida albicans to 5-fluorocytosine (5FC) demonstrated a high rate of resistance (85%) for serogroup B strains, more frequently isolated in Africa, and a low incidence (<1%) for serogroup A, predominating among Whites (Drouhet et al., 1974). Determination of the electrophoretic mobility of various strains did not provide a correlation between the charged groups of the surface and their phenotype to 5FC and antigenic groups. Adsorption of the surface antigens with a hyperimmune antiserum did not modify the phenotypic expression of Candida to 5FC. Electron microscopy studies revealed that susceptible strains had an additional granular layer dividing the inner stratum into two parts. After trypsin digestion of these strains, the disappearance of this layer was concomitantly associated with the emergence of resistance. Thus, it appears that the cell wall contains a proteinic material, which is located in the interior of the electron-transparent region and acts in the metabolism of 5FC.