Effect of adsorbed protein on hydroxyapatite zeta potential and Streptococcus mutans adherence

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Abstract
The adherence of S. mutans PK1 to hydroxylapatite discs pretreated with various acidic and basic proteins in imidazole buffer was studied. Adsorption of a basic protein onto an hydroxylapatite disc enhanced or had no effect on bacterial adherence; adsorption of an acidic protein reduced adherence. The effect of adsorbed protein on bacterial adherence was of short and long range. The long-range effect of the acidic proteins in reducing the number of bacteria adhering to hydroxylapatite was related to protein adsorption causing an increase in surface net negative charge, as shown by zeta potential measurement. Basic protein produced a net positive surface charge which facilitated adherence. Within the acidic protein group, the acidic residue percentage of the adsorbed protein was negatively correlated with the number of bacteria adhering; the nonpolar residue percentage was positively correlated with bacterial adherence. Within the basic protein group, the basic residue percentage was correlated with the number of cells adhering. Thus, short-range hydrophobic and ionic interactions are involved in bacterial adherence to protein-coated hydroxylapatite.