No abstract

The adherence of Candida albicans to acrylic was measured in vitro after growth of the yeast to stationary phase in defined medium containing glucose, sucrose, galactose, fructose, or maltose as the carbon source. In each case, yeast adherence was proportional to the concentration of sugar in the growth medium, but equimolar concentrations of different sugars promoted adherence to different extents. In vitro adherence was further increased by the addition of divalent cations to assay mixtures but was inhibited when saliva-treated acrylic strips were used or when yeasts were suspended in mixed saliva during the assay. The rate of spheroplast formation of yeasts grown in media containing a 500 mM concentration of the different sugars correlated well with the relative adherence of the cells to acrylic. Galactose-grown yeasts were most resistant to spheroplast formation with Zymolyase-5000 and most adherent to acrylic, whereas fructose-grown organisms were least resistant to spheroplast formation and least adherent to acrylic. These results indicate that when grown to stationary phase in media containing high concentrations of certain sugars, C. albicans undergoes a change in cell surface composition which facilitates its adherence to acrylic surfaces. Electron microscopy of yeasts harvested from such media revealed the presence of an additional surface layer which may be responsible for this enhanced adherence.

A comparison was made of the adherence to acrylic and to human buccal epithelial cells of seven strains of Candida albicans isolated from active infections (I strains) and two strains obtained from asymptomatic carriers (C strains). After growth in defined medium containing a relatively low concentration (50 mM) of glucose as the carbon source, the adherence of I and C strains to either surface was similar and all strains were sensitive to spheroplast formation with Zymolyase 5000. Growth in medium containing a high concentration (500 mM) of sucrose or galactose enhanced the adherence of I strains up to 5and 11-fold, respectively, and there were corresponding increases in resistance to spheroplast formation. Sucroseor galactose-grown C strains showed only small increases in adherence and remained relatively sensitive to spheroplast formation. When inoculated intravenously into mice, I strains grown in 500 mM sucrose were up to five times more virulent than organisms grown in 50 mM glucose, while I strains grown in 500 mM galactose showed a 5to 24-fold increase in virulence. Fifty percent lethal doses obtained for C strains were similar after growth on all three carbon sources. We conclude that I strains are able to modify their surface composition in response to high concentrations of certain sugars in the growth environment. Such modification can enhance both their ability to adhere to surfaces and their virulence. C strains lack this capability, or possess it to a lower degree, and may therefore have a lower pathogenic potential.

~ ~~ ~~Extracellular polymeric material (EP) was isolated from culture supernatants of Candida albicans grown on carbon sources (50 mM-glucose, 500 mM-SUCrOSe or 500 mM-galactose) known to promote yeast adhesion to different extents. Galactose-grown yeasts, which are the most adherent, produced more EP than sucrose-grown organisms, particularly after incubation for 5 d, while glucose-grown yeasts (the least adherent) gave the lowest yield. EP produced on all three carbon sources was of similar composition and contained carbohydrate (65 to 82%; mannose with some glucose), protein (7 %), phosphorus (0.5 %) and glucosamine (1 -5 %).Serological studies indicated that these EP preparations were immunologically identical but that galactose-grown yeasts had more antigenic determinants than sucrose-grown organisms while glucose-grown yeasts had the fewest determinants. Antigenic differences were apparent between EP preparations of some strains of C. albicans. Pretreatment of acrylic strips with EP to form a polymeric coating promoted yeast adhesion to the acrylic surface, but similar pretreatment of buccal epithelial cells with EP inhibited subsequent yeast adhesion. These results indicate that EP originates from the cell surface of C. albicans and that it contains the surface component(s), probably mannoprotein in nature, responsible for yeast adhesion.

Pretreatment of denture acrylic with nystatin, amphotericin B and chlorhexidine gluconate significantly reduced the subsequent adherence of Candida species to acrylic, although chlorhexidine and nystatin were more effective than amphotericin B. The duration of chlorhexidine-mediated inhibition of adherence (up to 19 days) was much longer than that of amphotericin B (24 h) or nystatin (48 h). Exposure of stationary-phase cells of Candida species for a short period to sublethal concentrations of chlorhexidine, or growth of Candida species with sublethal concentrations of chlorhexidine for 24 h resulted in a reduction in the ability of the yeasts to adhere to denture acrylic. The organisms grown in the presence of chlorhexidine were more susceptible to spheroplasting with Zymolyase 20T, indicating that chlorhexidine affects the cell surface composition of Candida species.