Comparative hydrophobicities of oral bacteria and their adherence to salivary pellicles

Oral bacteria were found to differ in their surface hydrophobicities as determined by their ability to adsorb to hexadecane. Strains of Actinomyces viscosus, A. naeslundii, Streptococcus sanguis, S. mitis, and Bacteroides gingivalis proved highly hydrophobic. Strains of B. intermedius, S. salivarius, S. mutans, and B. melaninogenicus were less hydrophobic, whereas strains of Actinobacillus actinomycetemcomitans were hydrophilic. An overall correlation was noted between the adsorption of bacteria to hexadecane and their numbers which attached to experimental salivary pellicles formed on hydroxyapatite surfaces. This suggests that hydrophobic bonding plays an important role in this process. Pellicles prepared from saliva which had been extracted with chloroform-methanol to remove lipids adsorbed comparable numbers of S. sanguis and A. viscosus and increased numbers of S. mutans. Analyses of adsorption isotherms indicated that pellicles formed from lipid-depleted saliva contained increased numbers of binding sites for the S. mutans strains studied, and this likely accounts for their enhanced adsorption. Absorption of saliva with 10% octyl or phenyl Sepharose reduced the protein content of saliva by almost half, but the numbers of bacteria which attached to pellicles prepared from such absorbed saliva were similar to or higher than those which attached to control pellicles. These observations suggest that saliva does not contain unique highly hydrophobic salivary macromolecules which serve as essential pellicle receptors for the bacteria studied. The data obtained are consistent with the view that hydrophobic bonding together with interactions between complementary molecules are involved in bacterial attachment to salivary pellicles on teeth.