Interaction of two oral streptococcal strains with physicochemically characterized fluorosilane diffusion gradient surfaces

Gradient surfaces have a defined variation in surface chemistry along their length that allow study of the influence of substratum wettability on bioa dhesion phenomena along their length in relation with a controlled surface chemistry. (Tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchlorosilane ( MCFS) diffusion gradients were made on glass and characterized by advancing and receding water contact angles and scanning X-ray photoelectron spectro scopy. Model calculations demonstrated that the hydrophobic ends of these g radients were only 50% covered by MCFS, which could be confirmed by atomic force microscopy showing hydrophobic patches. Therewith, bacteria can inter act with either hydrophobic or hydrophilic patches on the hydrophobic end o f a diffusion gradient, while on the hydrophilic end there is no such choic e. By use of a parallel plate flow chamber, the position-bound adhesion, in cluding initial deposition rates and numbers of adhering bacteria after 3 h , of two different oral streptococcal strains was studied along the lengths of MCFS gradients. Streptococcus oralis J22 did not show any position-boun d adhesion along the length of a gradient surface. The organism also had si milar adhesion behavior on homogeneous, hydrophobic FEP-Teflon as on hydrop hilic glass. Streptococcus sobrinus HG1025, however, adhered a-fold better to the hydrophobic end of a MCFS gradient than to its hydrophilic end, whil e also on homogeneous, hydrophobic FEP-Teflon adhesion was more extensive t han on hydrophilic glass. When streptococci adhering along the length of a gradient were exposed to a passing liquid-air interface,no position-bound d etachment was observed for any of the strains, but upon perfusion of the fl ow chamber with a detergent solution S. sobrinus HG1025 detached less from the hydrophobic end than from the hydrophilic end of the gradient. This stu dy demonstrates, using MCFS diffusion gradients; that the sensitivity of ba cterial strains to differences in substratum hydrophobicity, originating fr om a known chemical heterogeneity, is strain-dependent.