Adhesion of Lactococcus lactis to model substrata: direct study of the interface

The adhesion of Lactococcus lactis harvested in the exponential and stationary growth phases was examined on glass and on polystyrene with cells resuspended in water. A low adhesion density was observed with exponential cells whatever the substratum. Stationary cells adhered in large amount on polystyrene and not on glass. This adhesion behavior cannot be explained simply in terms of physicochemical properties of the surfaces. The attention is drawn on particular aspects which are not taken into consideration in classical approaches of cell adhesion. Atomic force microscopy showed that, after a forced contact, the bacterial surface sticks to the retracting AFM probe, indicating that the force applied when the cell comes in contact with the substratum may influence its adhesion. This may affect the relevance of adhesion tests in laminar conditions with respect to real situations. The X-ray photoelectron spectroscopy analysis of the substratum surface after detachment of adhering cells, on the one hand, and of evaporated cell supernatants, on the other hand, revealed that extracellular substances were released by L. lactis in the aqueous phase and at cell-substratum interface. They may have a critical effect on cell adhesion by increasing the ionic strength of the solution confined between the cells and the substrata and by bringing macromolecules at the interface. (C) 2001 Elsevier Science B.V. All rights reserved.