Correlation between reduction of surface hydrophobicity of S. aureus and the decrease in its adhesiveness induced by subinhibitory concentrations of brodimoprim.

Hydrophobic interactions are involved in the mechanism of adhesion of a variety of bacteria to host tissues. Bacterial attachment to human cells is modulated by a change in interfacial free energy and this is correlated with surface hydrophobicity of bacterial cells. In S. aureus (one ATCC25923+four clinical isolates) hydrophobicity before and after incubation with subinhibitory concentrations (sub-MICs) of brodimoprim (BMP), a dimethyoxypyrimidine recently entered clinical practice, was measured by sessile drop technique as the contact angle. BMP is a new molecule derived from trimethoprim by substitution of the OCH3 group in position 4 of the benzyl-ring with a bromine atom. Bacterial adhesiveness of the same S. aureus strains was measured under the same experimental conditions. BMP significantly decreased the surface hydrophobicity of S. aureus strains at one-half MIC and one-quarter MIC. At sub-MICs concentrations BMP also reduced the adhesiveness to human epithelial buccal cells but this effect was significant down to one-sixteenth MIC. The two phenomena are correlated and hydrophobicity is involved in bacterial adhesiveness but the molecular mechanisms for the two phenomena do not completely overlap, with adhesiveness the more complex and based on a system involving both the bacteria and the epithelial cells with their specific surface characteristics.