Surface hydrophobicity and surface free energy of Actinobacillus actinomycetemcomitans strains from human periodontitis.

The surface properties of five freshly isolated clinical strains of Actinobacillus actinomycetemcomitans and a non-sticky, non-cohesive colonial variant were characterized. On growth in serum-containing and serum-free media, the primary isolates had a high surface free energy, corresponding with the low hydrophobicity observed, using as assay adsorption to hexadecane. The dispersion component of the surface free energy was significantly lower upon growth in serum-free medium. In the electron microscope the cells appeared covered with vesicles. In sharp contrast, the colonial variant had a very low surface free energy but still showed a low hydrophobicity in the hexadecane assay. Expression of the surface free energy characteristics in serum-grown cultures appeared strongly dependent on cell treatment, suggesting a significant influence of an adsorbed proteinaceous layer. The cells of the variant strain generally carried fewer surface vesicles. No major difference was observed in the outer membrane protein composition between parent and variant strain.