Removal forces and adhesion properties of Saccharomyces cerevisiae on glass substrates probed by optical tweezer

In agroindustry, the hygiene of solid surfaces is of primary importance in order to ensure that products are safe for consumers. To improve safety, one of the major ways consists in identifying and understanding the mechanisms of microbial cell adhesion to nonporous solid surfaces or filtration membranes. In this paper we investigate the adhesion of the yeast cell Saccharomyces cerevisiae (about 5 mu m in diameter) to a model solid surface, using well-defined hydrophilic glass substrates. An optical tweezer device developed by Piau [J. Non-Newtonian Fluid Mech. 144, 1 (2007)] was applied to yeast cells in contact with well-characterized glass surfaces. Two planes of observation were used to obtain quantitative measurements of removal forces and to characterize the corresponding mechanisms at a micrometer length scale. The results highlight various adhesion mechanisms, depending on the ionic strength, contact time, and type of yeast. The study has allowed to show a considerable increase of adhering cells with the ionic strength and has provided a quantitative measurement of the detachment forces of cultured yeast cells. Force levels are found to grow with ionic strength and differences in mobility are highlighted. The results clearly underline that a microrheological approach is essential for analyzing the adhesion mechanisms of biological systems at the relevant local scales.