Determination of the van der Waals, electron donor and electron acceptor surface tension components of static Gram-positive microbial biofilms

A large number of studies have shown the influence of the physico-chemical properties of a surface on microbial adhesion phenomenon. In this study, we considered that the presence of a bacterial biofilm may be regarded as a “conditioning film” that may modify the physico-chemical characteristics of the support, and thus the adhesion capability of planktonic micro-organisms coming into contact with this substratum. In this context, we adapted a protocol for biofilm formation that allows, under our experimental conditions, contact angle measurements, the reference method to determine the energetic surface properties of a substratum. This made it possible to determine the van der Waals, electron acceptor and electron donor properties of static biofilms grown at 25°C on stainless-steel slides with six Gram-positive bacteria isolated in dairy plants. A variance analysis indicated significant effects (P<0.05) of the bacterial strains and of the physiological state of the micro-organisms (planktonic or sessile) on the contact angles. To link the energetic properties of the six biofilms with direct adhesion experiments, we measured the affinity of fluorescent carboxylate-modified polystyrene beads for the different biofilm surfaces. The results correlated best with the electron-acceptor components of the biofilm surface energies, stressing the importance of Lewis acid–base interactions in adhesion mechanisms.