The effect of surface free energy and medium surface tension on bacterial attachment to solid surfaces

The process of bacterial attachment to solid surfaces comprises three components, i.e., the bacterial surface, the substratum, and the liquid medium, all of which have been shown to affect the thermodynamics of adhesion. Different bacterial strains and phenotypes can differ considerably with respect to cell surface composition, and thus surface free energy. Accordingly, attachment ability ranges from bacteria which attach readily to surfaces to those which have little adhesive ability. Influence of substratum properties was shown by the relationship between numbers of attached bacteria and substratum work of adhesion for water (WA). Maximum attachment occurred within a substratum WA range of 75 to 105 mJ m−2, but the WA at peak attachment was not the same for all bacteria tested. The liquid medium influences attachment because of the (i) interaction between water and the substratum and bacterial surfaces and the presence of (ii) dissolved macromolecules, which tend to adsorb on surfaces, and (iii) surface active agents which influence surface tension and thus the thermodynamics of adhesion. Dimethyl sulfoxide and a series of low-molecular-weight alcohols were shown to affect numbers of attached cells by affecting liquid surface tension