Hydrophobic interactions and the adherence of Streptococcus sanguis to hydroxylapatite

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Abstract
S. sanguis demonstrated a high affinity for hydrocarbon solvents. When aqueous suspensions of the organism were mixed with hexadecane or toluene, the cells tended to bind to the nonaqueous solvent. Increases in temperature resulted in a greater affinity of cells for hexadecane. Interaction between the cells and hexadecane was also enhanced by dilute aqueous NaCl and by low pH (pH < 5). Thus, the cell surface of S. sanguis evidently has hydrophobic properties. Isolated cell walls also tended to partition into the nonaqueous solvent. Amino acid analyes of the walls revealed the presence of several amino acids which possess hydrophobic side chains. The hydrophobic amino acids associated with the cell wall may contribute to the hydrophobicity of intact S. sanguis. When the adherence of S. sanguis to saliva-coated hydroxylapatite was measured, hydrophobic bond-disrupting agents, such as the Li+ cation, the SCN- anion and sodium dodecyl sulfate, were capable of inhibiting the cell-hydroxylapatite union. Both urea and tetramethylurea were inhibitors of the adherence, although the latter reagent was the superior inhibitor. Evidently, the adherence of S. sanguis to saliva-coated smooth surfaces is at least partially dependent on the formation of hydrophobic bonds between the cell and adsorbed salivary proteins. Hydrophobic bonding may contribute to cooperative interactions involving S. sanguis and saliva-coated hydroxylapatite.