Factors governing adherence of Candida species to plastic surfaces

The ability of Candida albicans and Candida spp. to adhere to inert polymeric surfaces may allow these organisms direct ingress into the human host. Biophysical characterization of this adherence shows that the forces responsible for such adherence are attractive London-van der Waals forces (or hydrophobic forces) and electrostatic forces. The hydrophobic affinity of yeasts was determined by (i) a water-hydrocarbon two-phase assay and by (ii) measurement of the contact angle (theta) of a liquid droplet on a monolayer of yeast cells. The hydrophobicity of the yeasts correlated with the tendency of yeasts to adhere to polystyrene and was reduced in the presence of Tween 20. The adherence of yeasts to polymers of increasing hydrophobicity (determined by the contact angle method) was directly proportional to theta. Yeast surface charges were altered by selectively blocking amino and carboxyl groups. The more positively charged yeasts adhered in greater numbers. Increasing the molarity of NaCl increased yeast adherence. These forces probably contribute to the negative cooperativity (determined by Scatchard and Hill plot) that characterizes the adherence of yeasts to polymers.