Surface thermodynamics of bacterial adhesion

TLDR

Bacterial adhesion to polymeric surfaces is governed by thermodynamic surface‑tension interactions, with hydrophilic substrates favoring adhesion when bacterial surface tension exceeds that of the medium and the reverse when the medium’s surface tension is higher. The study aimed to design an experimental protocol guided by thermodynamic principles to quantify bacterial adhesion. Bacterial suspensions (10⁸ cells mL⁻¹) were exposed to Teflon, polyethylene, polystyrene, acetal, and sulfonated polystyrene for 30 min at 20 °C, then rinsed and quantified by image analysis, with the medium (Hanks balanced salt solution) modified by varying DMSO concentrations. Adhesion densities matched thermodynamic predictions, enabling determination of bacterial surface tensions that agreed with values obtained by other methods.

Abstract

The adhesion of five strains of bacteria, i.e., Staphylococcus aureus (strain 049), Staphylococcus epidermidis (strain 047), Escherichia coli (strains 055 and 2627), and Listeria monocytogenes, to various polymeric surfaces was studied. The design of the experimental protocol was dictated by thermodynamic considerations. From the thermodynamic model for the adhesion of small particles from a suspension onto a solid substratum, it follows that the extent of adhesion is determined by the surface properties of all three phases involved, i.e., the surface tensions of the adhering particles, of the substrate, and of the suspending liquid medium. In essence, adhesion is more extensive to hydrophilic substrata (i.e., substrata of relatively high surface tension) than to hydrophobic substrata, when the surface tension of the bacteria is larger than that of the suspending medium. When the surface tension of the suspending liquid is larger than that of the bacteria, the opposite pattern of behavior prevails. Suspensions of bacteria at a concentration of 10(8) microorganisms per ml were brought into contact with several polymeric surfaces (Teflon, polyethylene, polystyrene, and acetal and sulfonated polystyrene) for 30 min at 20 degrees C. After rinsing, the number of bacteria adhering per unit surface area was determined by image analysis. The surface tension of the suspending medium. Hanks balanced salt solution, was modified through the addition of various amounts of dimethyl sulfoxide. It was found that the number of bacteria adhering per unit surface area correlates well with the thermodynamic predictions and that these data may be used to determine the surface tension of the different bacterial species. The surface tensions of the bacteria obtained in this fashion are in excellent agreement with those obtained by other methods.