STREPTOCOCCUS-THERMOPHILUS AND ITS BIOSURFACTANTS INHIBIT ADHESION BYCANDIDA SPP. ON SILICONE-RUBBER

The adhesion of yeasts, two Candida albicans and two Candida tropicali s strains isolated from naturally colonized voice prostheses, to silic one rubber with and without a salivary conditioning film in the absenc e and presence of adhering Streptococcus thermophilus B, a biosurfacta nt-releasing dairy isolate, was studied, Coverage of 1 to 4% of the su rface of silicone rubber substrata with adhering S. thermophilus B gav e significant reductions in the initial yeast adhesion regardless of t he presence of a conditioning film. Mechanistically, this interference in yeast adhesion by S. thermophilus B was not due to direct physical effects but to biosurfactant release by the adhering bacteria, becaus e experiments with S. thermophilus B cells that had released their bio surfactants prior to adhesion to silicone rubber and competition with yeasts did not show interference with initial yeast adhesion, The amou nts of biosurfactants released were highest for mid-exponential-and ea rly-stationary-phase bacteria (37 mg.g of cells(-1) [dry weight]), but biosurfactants released by stationary-phase bacteria (14 mg.g of cell s(-1) [dry weight]) were the most surface active, The crude biosurfact ants released were mixtures of various components, with a glycolipid-l ike component being the most surface active, A lipid-enriched biosurfa ctant fraction reduced the surface tension of an aqueous solution to a bout 35 mJ.m(-2) at a concentration of only 0.5 mg.ml(-1). The amount of biosurfactant released per S. thermophilus B cell was estimated to be sufficient to cover approximately 12 times the area of the cross se ction of the bacterium, making biosurfactant release a powerful defens e weapon in the postadhesion competition of the bacterium with microor ganisms such as yeasts, Preadsorption of biosurfactants to the silicon e rubber prior to allowing yeasts to adhere was as effective against C . albicans GB 112 adhesion as covering 1 to 2% of the silicone rubber surface with adhering S. thermophilus B, but a preadsorbed biosurfacta nt layer was less effective against C, tropicalis GB 9/9.