Changes on the physico-chemical surface properties and adhesion behaviour of Enterococcus faecalis by the addition of serum or urine to the growth medium

Abstract

The initial microbial adhesion of bacteria to different surfaces seems to be mediated by physico-chemical forces and this is the reason why the physico-chemical surface characterisation of bacteria has recently gained interest. In this context, the adhesion of different microorganisms to biological substrata has been described from a physico-chemical point of view, aiming to simulate, as closely as possible, the conditions of interest. On this basis, the objective of this work is to characterise the surface of Enterococcus faecalis ATCC29212 through hydrophobicity, surface free energy and zeta potential at 37 °C, when cells grow in Trypticase Soy Broth (TSB) and TSB supplemented with serum or urine. These variations are used to provide a theoretical description of the bacterial adhesion to glass by interaction free energy, which is verified with experimental results employing a parallel plate flow chamber set at 37 °C, to simulate the conditions of flow inside the human body. The results show that the addition of serum to the growth medium increases the hydrophobicity and isoelectric point (i.e.p.) of the microorganisms, and this could indicate an increase in the protein content on the cell surface. However urine does not introduce a change in the above magnitudes. At short separation distances between the cells and the substratum, the interaction free energy predicts a favourable adhesion for serum-grown cells while non-favourable adhesion is expected for control (TSB-grown cells) and urine-grown cells. These results are in agreement with the experimental adhesion data, obtained with the flow chamber.