Quantification of Polymer Interactions in Bacterial Adhesion

Abstract

Adhesion of bacteria to solids is governed by van der Waals, electrostatic, and acid−base (hydrophobic) interactions, which are combined in an extended DLVO model (DLVO−AB) and by interactions of bacterial surface polymers with the solid surfaces. A method to calculate polymer interactions was not available yet, and their existence had been inferred only qualitatively from the deviation of the actual adhesion from DLVO−AB-based expectations. Here, we present attempts (i) to quantify polymer interactions from this deviation and (ii) to calculate them independently as the sum of repulsive and attractive contributions. Repulsion was assumed to result from the resistance of the polymer layer against compression. Its calculation was most sensitive to the packing density of the polymers in the cell envelope. Attraction was assumed to origin from polymer adsorption to the surface and was calculated on the basis of adsorption data of isolated surface polymers. Comparison of total interaction energy curves with adhesion of six Gram-negative bacteria to glass showed that the low adherence of five strains may have resulted from dominant polymer repulsion, i.e., hardly compressible cell envelopes hindered the bacteria to approach the energy minima resulting from DLVO−AB interactions. One strain adhered readily, possibly because polymer repulsion was low and polymer attraction and DLVO−AB forces dominated the overall interaction.