Surface aggregation of Candida albicans on glass in the absence and presence of adhering Streptococcus gordonii in a parallel-plate flow chamber: A surface thermodynamical analysis based on acid-base interactions

Adhesive interactions between yeasts and bacteria are important in the main tenance 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 betwee n C. albicans ATCC 10261 and S. gordonii NCTC 7869 adhering on glass. Conta ct angles with different liquids and the zeta 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 adher e to the bottom glass plate of the flow chamber to different seeding densit ies, and subsequently deposition of yeasts was monitored with an image anal ysis system, yielding the degree of initial surface aggregation of the adhe ring yeasts and their spatial arrangement in a stationary end point. Irresp ective of growth temperature, the yeast cells appeared uncharged in TNMC bu ffer, but yeasts grown at 37 degrees C were intrinsically more hydrophilic and had an increased electron-donating character than cells grown at 30 deg rees C. All yeasts showed surface aggregation due to attractive Lifshitz-va n der Waals forces. In addition, acid-base interactions between yeasts, yea sts and the glass substratum, and yeasts and the streptococci were attracti ve for yeasts grown at 30 degrees C, but yeasts grown at 37 degrees C only had favorable acid-base interactions with the bacteria, explaining the posi tive relationship between the surface coverage of the glass by streptococci and the surface aggregation of the yeasts. (C) 1999 Academic Press.