Surface Aggregation ofCandida albicanson Glass in the Absence and Presence of AdheringStreptococcus gordoniiin a Parallel-Plate Flow Chamber: A Surface Thermodynamical Analysis Based on Acid–Base Interactions

Abstract

Adhesive interactions between yeasts and bacteria are important in the maintenance of infectious mixed biofilms on natural and biomaterial surfaces in the human body. In this study, the extended DLVO (Derjaguin–Landau–Verwey–Overbeek) approach has been applied to explain adhesive interactions betweenC. albicansATCC 10261 andS. gordoniiNCTC 7869 adhering on glass. Contact angles with different liquids and the ζ potentials of both the yeasts and bacteria were determined and their adhesive interactions were measured in a parallel-plate flow chamber.Streptococci were first allowed to adhere to the bottom glass plate of the flow chamber to different seeding densities, and subsequently deposition of yeasts was monitored with an image analysis system, yielding the degree of initial surface aggregation of the adhering yeasts and their spatial arrangement in a stationary end point. Irrespective of growth temperature, the yeast cells appeared uncharged in TNMC buffer, but yeasts grown at 37°C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30°C. All yeasts showed surface aggregation due to attractive Lifshitz–van der Waals forces. In addition, acid–base interactions between yeasts, yeasts and the glass substratum, and yeasts and the streptococci were attractive for yeasts grown at 30°C, but yeasts grown at 37°C only had favorable acid–base interactions with the bacteria, explaining the positive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts.