The influence of a pellicle on streptococcal adhesion was studied. A "ripened" two-hour salivary pellicle and an "early" five-minute salivary pellicle were formed on human enamel and artificial solid substrata with varying surface free-energies. Three strains of oral streptococci, also with widely different surface free-energies, were used for adhesion studies. Pellicle formation and streptococcal adhesion took place at a constant shear rate of 21 s-1. Adhesion of S. mitis BMS to bare and pellicle-covered enamel was low and not significantly affected by the presence of a pellicle (0.7 x 10(6) and 0.6 x 10(6) cells.cm-2, resp.), whereas the numbers of S. sanguis 12 and S. mutans NS adhering to bare enamel (4.2 x 10(6) cells.cm-2 and 13.8 x 10(6) cells, cm-2, resp) were significantly reduced by the presence of a pellicle. This reduction was almost complete after only five minutes of salivary protein adsorption (1.9 x 10(-6) and 1.1 x 10(6) cells.cm-2 for S. sanguis and S. mutans, resp.) but further reduced for S. sanguis adhering to a ripened pellicle (0.7 x 10(6) cells.cm-2). The numbers of streptococci adhering at equilibrium to bare enamel could be fitted to a thermodynamically based model, which was previously described for bacterial adhesion to homogenous artificial substrata. Streptococcal adhesion to artificial substrata exposed to saliva was low, and the differences among uncoated materials were markedly reduced even after only five minutes' exposure to saliva.
A flow cell system was developed which allowed the study of bacterial adhesion to solid substrata at well-defined shear rates. In addition, the system enabled the solid surfaces to be coated with a proteinaceous film under exactly the same shear conditions. In this flow cell system, adhesion of three strains of oral streptococci from a phosphate-buffered solution onto three different substrata was studied as a function of time in the absence and presence of a bovine serum albumin (BSA) coating at a shear rate of 21 s-'. To obtain a wide range in surface free energies (y) representative strains (Yb 38-1 17 mJ m-2) and solid substrata (y, 20-109 mJ m-') were selected. The number of bacteria adhering was counted microscopically. In the absence of a BSA coating a linear relation was found between the number of bacteria adhering at saturation (nb.,) and the calculated interfacial free energy of adhesion (AFadh) for each of the three strains. In the presence of a BSA coating the number of bacteria adhering was greatly decreased in all cases. However, despite the presence of the BSA coating there was still a linear relation between the number of bacteria adhering at saturation and the interfacial free energy of adhesion, calculated on the basis of the surface free energy of the uncoated substrata. It can be concluded that the bare, uncoated substratum still influenced bacterial adhesion in spite of the marked influence of a BSA coating.
The effects of high molecular weight mucins, adsorbed on enamel and artificial solid substrata with various surface free energies, on oral streptococcal adhesion have been investigated. For the adhesion studies, 3 strains of oral streptococci with widely different surface free energies were used. The substrata were precoated with mucins with a molecular mass >10 5 Da. The adhesion of S. mutans NS to mucin coated, hydrophobic FEP-teflon was significantly increased by the presence of the mucin coating, whereas the adhesion of S. mutans NS to more hydrophilic substrata such as cellulose acetate, glass and enamel decreased. In addition, the adhesion of S. sanguis 12 and S. mitis BMS to mucin-coated surfaces decreased slightly. However, adhesion of S. sanguis to FEP-teflon remained unaltered.Unlike S. mitis, S. mutans and S. sanguis are known to possess specific carbohydrate receptor sites (lectins) which may interact with the carbohydrate part of adsorbed mucins. From the decrease in the adhesion of S. mutans to mucin-coated glass, it is concluded that mucins adsorb to glass with their polar carbohydrate part. On the other hand, it is hypothesized that mucins adsorb to FEP-teflon with their apolar protein part, thereby revealing their carbohydrate part towards the solution phase and stimulating the adhesion of S. mutans NS, while leaving the adhesion of S. sanguis 12 unaltered. Further evidence for this adsorption model of mucins is provided by contact angle measurements.
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