Adhesive interactions between medically important yeasts and bacteria.

Yeasts are being increasingly identified as important organisms in human infections. Adhesive interactions between yeasts and bacteria may contribute to yeast retention at body sites. Methods for studying adhesive interactions between bacterial strains are well known, and range from simple macroscopic methods to flow chamber systems with complex image analysis capabilities. The adhesive interactions between bacteria and yeasts have been studied employing several of the methods originally developed for studying adhesive interactions between bacteria. However, in many of the methods employed the larger size of the yeasts as compared with bacteria results in strong sedimentation of the yeasts, often invalidating the method adapted. In addition, most methods are semi-quantitative and do not properly control mass transport. Consequently, adhesive interaction mechanisms between yeasts and bacteria identified hitherto, including lectin binding and protein-protein interactions, must be regarded with caution. Extensive physico-chemical characteristics of yeast cell surfaces are not available and a physico-chemical mechanism has not yet been put forth. A new method for quantifying adhesive interactions between yeasts and bacteria is proposed, based on the use of a parallel plate flow chamber, in which the influence of adhering bacteria upon the kinetics of yeast adhesion and aggregation of the adhering yeasts is quantitatively evaluated, under carefully controlled mass transport.